Guide to the Secure Configuration of Red Hat Enterprise Linux 7

with profile STIG for Red Hat Enterprise Linux 7 Workstation
This is a *draft* profile for STIG. This profile is being developed under the DoD consensus model to become a STIG in coordination with DISA FSO.

Where is the RHEL7 STIG?

  • Question: May I deploy a product if no STIG exists?
    Answer: Yes, based on mission need and with DAA approval.
  • Question: What do I use if there is no STIG?
    Answer: DISA FSO developed Security Requirement Guides (SRGs) to address technology areas. In the absence of a STIG, an SRG can be used to determine compliance with DoD policies. If there is no applicable SRG or STIG, industry or vendor recommended practices may be used. Examples include Center for Internet Security Benchmarks, Payment Card Industry requirements or the vendor's own security documentation.
Source: http://iase.disa.mil/stigs/Pages/faqs.aspx#STIG

This guide presents a catalog of security-relevant configuration settings for Red Hat Enterprise Linux 7. It is a rendering of content structured in the eXtensible Configuration Checklist Description Format (XCCDF) in order to support security automation. The SCAP content is is available in the scap-security-guide package which is developed at https://www.open-scap.org/security-policies/scap-security-guide.

Providing system administrators with such guidance informs them how to securely configure systems under their control in a variety of network roles. Policy makers and baseline creators can use this catalog of settings, with its associated references to higher-level security control catalogs, in order to assist them in security baseline creation. This guide is a catalog, not a checklist, and satisfaction of every item is not likely to be possible or sensible in many operational scenarios. However, the XCCDF format enables granular selection and adjustment of settings, and their association with OVAL and OCIL content provides an automated checking capability. Transformations of this document, and its associated automated checking content, are capable of providing baselines that meet a diverse set of policy objectives. Some example XCCDF Profiles, which are selections of items that form checklists and can be used as baselines, are available with this guide. They can be processed, in an automated fashion, with tools that support the Security Content Automation Protocol (SCAP). The DISA STIG for Red Hat Enterprise Linux 7, which provides required settings for US Department of Defense systems, is one example of a baseline created from this guidance.
Do not attempt to implement any of the settings in this guide without first testing them in a non-operational environment. The creators of this guidance assume no responsibility whatsoever for its use by other parties, and makes no guarantees, expressed or implied, about its quality, reliability, or any other characteristic.
Profile TitleSTIG for Red Hat Enterprise Linux 7 Workstation
Profile IDxccdf_org.ssgproject.content_profile_stig-rhel7-workstation-upstream

Revision History

Current version: 0.1.31

  • draft (as of 2017-03-31)

Platforms

  • cpe:/o:redhat:enterprise_linux:7
  • cpe:/o:redhat:enterprise_linux:7::client
  • cpe:/o:redhat:enterprise_linux:7::computenode

Table of Contents

  1. System Settings
    1. Installing and Maintaining Software
    2. File Permissions and Masks
    3. SELinux
    4. Account and Access Control
    5. Network Configuration and Firewalls
    6. Configure Syslog
    7. System Accounting with auditd
  2. Services
    1. Obsolete Services
    2. Base Services
    3. Cron and At Daemons
    4. SSH Server
    5. System Security Services Daemon
    6. Network Time Protocol
    7. NFS and RPC
    8. FTP Server
    9. Network Routing
    10. SNMP Server

Checklist

contains 291 rules

System Settings   [ref]group

Contains rules that check correct system settings.

contains 229 rules

Installing and Maintaining Software   [ref]group

The following sections contain information on security-relevant choices during the initial operating system installation process and the setup of software updates.

contains 57 rules

Disk Partitioning   [ref]group

To ensure separation and protection of data, there are top-level system directories which should be placed on their own physical partition or logical volume. The installer's default partitioning scheme creates separate logical volumes for /, /boot, and swap.

  • If starting with any of the default layouts, check the box to "Review and modify partitioning." This allows for the easy creation of additional logical volumes inside the volume group already created, though it may require making /'s logical volume smaller to create space. In general, using logical volumes is preferable to using partitions because they can be more easily adjusted later.
  • If creating a custom layout, create the partitions mentioned in the previous paragraph (which the installer will require anyway), as well as separate ones described in the following sections.
If a system has already been installed, and the default partitioning scheme was used, it is possible but nontrivial to modify it to create separate logical volumes for the directories listed above. The Logical Volume Manager (LVM) makes this possible. See the LVM HOWTO at http://tldp.org/HOWTO/LVM-HOWTO/ for more detailed information on LVM.

contains 5 rules

Ensure /tmp Located On Separate Partition   [ref]rule

The /tmp directory is a world-writable directory used for temporary file storage. Ensure it has its own partition or logical volume at installation time, or migrate it using LVM.

Rationale:

The /tmp partition is used as temporary storage by many programs. Placing /tmp in its own partition enables the setting of more restrictive mount options, which can help protect programs which use it.

identifiers:  CCE-27173-4

references:  SC-32(1), 366, SRG-OS-000480-GPOS-00227, 1.1.1, RHEL-07-021340

Ensure /var Located On Separate Partition   [ref]rule

The /var directory is used by daemons and other system services to store frequently-changing data. Ensure that /var has its own partition or logical volume at installation time, or migrate it using LVM.

Rationale:

Ensuring that /var is mounted on its own partition enables the setting of more restrictive mount options. This helps protect system services such as daemons or other programs which use it. It is not uncommon for the /var directory to contain world-writable directories installed by other software packages.

identifiers:  CCE-26404-4

references:  SC-32(1), 1.1.5, 366, SRG-OS-000480-GPOS-00227, RHEL-07-021320

Ensure /var/log/audit Located On Separate Partition   [ref]rule

Audit logs are stored in the /var/log/audit directory. Ensure that it has its own partition or logical volume at installation time, or migrate it later using LVM. Make absolutely certain that it is large enough to store all audit logs that will be created by the auditing daemon.

Rationale:

Placing /var/log/audit in its own partition enables better separation between audit files and other files, and helps ensure that auditing cannot be halted due to the partition running out of space.

identifiers:  CCE-26971-2

references:  AU-4, AU-9, SC-32(1), 366, 1.1.8, SRG-OS-000480-GPOS-00227, RHEL-07-021330

Ensure /home Located On Separate Partition   [ref]rule

If user home directories will be stored locally, create a separate partition for /home at installation time (or migrate it later using LVM). If /home will be mounted from another system such as an NFS server, then creating a separate partition is not necessary at installation time, and the mountpoint can instead be configured later.

Rationale:

Ensuring that /home is mounted on its own partition enables the setting of more restrictive mount options, and also helps ensure that users cannot trivially fill partitions used for log or audit data storage.

identifiers:  CCE-80144-9

references:  SC-32(1), 366, 1208, 1.1.9, SRG-OS-000480-GPOS-00227, RHEL-07-021310

Encrypt Partitions   [ref]rule

Red Hat Enterprise Linux 7 natively supports partition encryption through the Linux Unified Key Setup-on-disk-format (LUKS) technology. The easiest way to encrypt a partition is during installation time.

For manual installations, select the Encrypt checkbox during partition creation to encrypt the partition. When this option is selected the system will prompt for a passphrase to use in decrypting the partition. The passphrase will subsequently need to be entered manually every time the system boots.

For automated/unattended installations, it is possible to use Kickstart by adding the --encrypted and --passphrase= options to the definition of each partition to be encrypted. For example, the following line would encrypt the root partition:

part / --fstype=ext4 --size=100 --onpart=hda1 --encrypted --passphrase=PASSPHRASE
Any PASSPHRASE is stored in the Kickstart in plaintext, and the Kickstart must then be protected accordingly. Omitting the --passphrase= option from the partition definition will cause the installer to pause and interactively ask for the passphrase during installation.

Detailed information on encrypting partitions using LUKS can be found on the Red Hat Documentation web site:
https://docs.redhat.com/docs/en-US/Red_Hat_Enterprise_Linux/7/html/Security_Guide/sec-Encryption.html

Rationale:

The risk of a system's physical compromise, particularly mobile systems such as laptops, places its data at risk of compromise. Encrypting this data mitigates the risk of its loss if the system is lost.

identifiers:  CCE-27128-8

references:  SC-13, SC-28(1), 1199, 2476, SRG-OS-000405-GPOS-00184, SRG-OS-000185-GPOS-00079, 3.13.16

Updating Software   [ref]group

The yum command line tool is used to install and update software packages. The system also provides a graphical software update tool in the System menu, in the Administration submenu, called Software Update.

Red Hat Enterprise Linux systems contain an installed software catalog called the RPM database, which records metadata of installed packages. Consistently using yum or the graphical Software Update for all software installation allows for insight into the current inventory of installed software on the system.

contains 7 rules

Ensure Red Hat GPG Key Installed   [ref]rule

To ensure the system can cryptographically verify base software packages come from Red Hat (and to connect to the Red Hat Network to receive them), the Red Hat GPG key must properly be installed. To install the Red Hat GPG key, run:

$ sudo rhn_register
If the system is not connected to the Internet or an RHN Satellite, then install the Red Hat GPG key from trusted media such as the Red Hat installation CD-ROM or DVD. Assuming the disc is mounted in /media/cdrom, use the following command as the root user to import it into the keyring:
$ sudo rpm --import /media/cdrom/RPM-GPG-KEY

Rationale:

Changes to software components can have significant effects on the overall security of the operating system. This requirement ensures the software has not been tampered with and that it has been provided by a trusted vendor. The Red Hat GPG key is necessary to cryptographically verify packages are from Red Hat.

identifiers:  CCE-26957-1

references:  CM-5(3), SI-7, MA-1(b), 1749, 366, Req-6.2, 1.2.2, 5.10.4.1, 3.4.8

Remediation Shell script:   (show)

Complexity:low
Disruption:low
Strategy:disable
# The two fingerprints below are retrieved from https://access.redhat.com/security/team/key
readonly REDHAT_RELEASE_2_FINGERPRINT="567E 347A D004 4ADE 55BA 8A5F 199E 2F91 FD43 1D51"
readonly REDHAT_AUXILIARY_FINGERPRINT="43A6 E49C 4A38 F4BE 9ABF 2A53 4568 9C88 2FA6 58E0"
# Location of the key we would like to import (once it's integrity verified)
readonly REDHAT_RELEASE_KEY="/etc/pki/rpm-gpg/RPM-GPG-KEY-redhat-release"

RPM_GPG_DIR_PERMS=$(stat -c %a "$(dirname "$REDHAT_RELEASE_KEY")")

# Verify /etc/pki/rpm-gpg directory permissions are safe
if [ "${RPM_GPG_DIR_PERMS}" -le "755" ]
then
  # If they are safe, try to obtain fingerprints from the key file
  # (to ensure there won't be e.g. CRC error).
  IFS=$'\n' GPG_OUT=($(gpg --with-fingerprint "${REDHAT_RELEASE_KEY}" | grep 'Key fingerprint ='))
  GPG_RESULT=$?
  # No CRC error, safe to proceed
  if [ "${GPG_RESULT}" -eq "0" ]
  then
    tr -s ' ' <<< "${GPG_RESULT}" | grep -vE "${REDHAT_RELEASE_2_FINGERPRINT}|${REDHAT_AUXILIARY_FINGERPRINT}" || {
      # If file doesn't contains any keys with unknown fingerprint, import it
      rpm --import "${REDHAT_RELEASE_KEY}"
    }
  fi
fi
Remediation Ansible snippet:   (show)

Complexity:medium
Disruption:medium
Strategy:restrict

- name: "Read permission of GPG key directory"
  stat:
    path: /etc/pki/rpm-gpg/
  register: gpg_key_directory_permission

  # It should fail, if it doesn't find any fingerprints in file - maybe file was not parsed well.
- name: "Read signatures in GPG key"
  shell: "gpg --with-fingerprint '/etc/pki/rpm-gpg/RPM-GPG-KEY-redhat-release' | grep 'Key fingerprint =' | tr -s ' ' | sed 's;.*= ;;g'"
  changed_when: False
  register: gpg_fingerprints

- name: "Set Fact: Valid fingerprints"
  set_fact:
     gpg_valid_fingerprints: ("567E 347A D004 4ADE 55BA 8A5F 199E 2F91 FD43 1D51" "43A6 E49C 4A38 F4BE 9ABF 2A53 4568 9C88 2FA6 58E0")
  
- name: "Import RedHat GPG key"
  rpm_key:
    state: present
    key: /etc/pki/rpm-gpg/RPM-GPG-KEY-redhat-release
  when:
    (gpg_key_directory_permission.stat.mode <= '0755')
    and ({{ gpg_fingerprints.stdout_lines | difference(gpg_valid_fingerprints) }} | length == 0)
    and (gpg_fingerprints.stdout_lines | length > 0)
    and (ansible_distribution == "RedHat")

Ensure gpgcheck Enabled In Main Yum Configuration   [ref]rule

The gpgcheck option controls whether RPM packages' signatures are always checked prior to installation. To configure yum to check package signatures before installing them, ensure the following line appears in /etc/yum.conf in the [main] section:

gpgcheck=1

Rationale:

Changes to any software components can have significant effects on the overall security of the operating system. This requirement ensures the software has not been tampered with and that it has been provided by a trusted vendor.
Accordingly, patches, service packs, device drivers, or operating system components must be signed with a certificate recognized and approved by the organization.
Verifying the authenticity of the software prior to installation validates the integrity of the patch or upgrade received from a vendor. This ensures the software has not been tampered with and that it has been provided by a trusted vendor. Self-signed certificates are disallowed by this requirement. Certificates used to verify the software must be from an approved Certificate Authority (CA).

identifiers:  CCE-26989-4

references:  CM-5(3), SI-7, MA-1(b), 1749, SRG-OS-000366-GPOS-00153, RHEL-07-020050, Req-6.2, 1.2.3, 5.10.4.1, 3.4.8

Remediation Shell script:   (show)

Complexity:low
Disruption:low
Strategy:disable

function replace_or_append {
  local config_file=$1
  local key=$2
  local value=$3
  local cce=$4
  local format=$5

  # Check sanity of the input
  if [ $# -lt "3" ]
  then
        echo "Usage: replace_or_append 'config_file_location' 'key_to_search' 'new_value'"
        echo
        echo "If symlinks need to be taken into account, add yes/no to the last argument"
        echo "to allow to 'follow_symlinks'."
        echo "Aborting."
        exit 1
  fi

  # Test if the config_file is a symbolic link. If so, use --follow-symlinks with sed.
  # Otherwise, regular sed command will do.
  if test -L $config_file; then
    sed_command="sed -i --follow-symlinks"
  else
    sed_command="sed -i"
  fi

  # Test that the cce arg is not empty or does not equal $CCENUM.
  # If $CCENUM exists, it means that there is no CCE assigned.
  if ! [ "x$cce" = x ] && [ "$cce" != '$CCENUM' ]; then
    cce="CCE-${cce}"
  else
    cce="CCE"
  fi

  # Strip any search characters in the key arg so that the key can be replaced without
  # adding any search characters to the config file.
  stripped_key=$(sed "s/[\^=\$,;+]*//g" <<< $key)

  # If there is no print format specified in the last arg, use the default format.
  if ! [ "x$format" = x ] ; then
    printf -v formatted_output "$format" $stripped_key $value
  else
    formatted_output="$stripped_key = $value"
  fi

  # If the key exists, change it. Otherwise, add it to the config_file.
  if `grep -qi $key $config_file` ; then
    $sed_command "s/$key.*/$formatted_output/g" $config_file
  else
    # \n is precaution for case where file ends without trailing newline
    echo -e "\n# Per $cce: Set $formatted_output in $config_file" >> $config_file
    echo -e "$formatted_output" >> $config_file
  fi

}

replace_or_append '/etc/yum.conf' '^gpgcheck' '1' 'CCE-26989-4'
Remediation Ansible snippet:   (show)

Complexity:low
Disruption:medium

- name: "Check existence of yum on Fedora"
  stat:
    path: /etc/yum.conf
  register: yum_config_file
  when: ansible_distribution == "Fedora"

# We can have yum also in Fedora, but probably not forever
- name: Ensure GPG check is globally activated (yum)
  ini_file:
    dest: "{{item}}"
    section: main
    option: gpgcheck
    value: 1
    create: False
  with_items: "/etc/yum.conf"
  when: ansible_distribution == "RedHat" or yum_config_file.stat.exists

- name: Ensure GPG check is globally activated (dnf)
  ini_file:
    dest: "{{item}}"
    section: main
    option: gpgcheck
    value: 1
    create: False
  with_items: "/etc/dnf/dnf.conf"
  when: ansible_distribution == "Fedora"

Ensure gpgcheck Enabled For All Yum Package Repositories   [ref]rule

To ensure signature checking is not disabled for any repos, remove any lines from files in /etc/yum.repos.d of the form:

gpgcheck=0

Rationale:

Verifying the authenticity of the software prior to installation validates the integrity of the patch or upgrade received from a vendor. This ensures the software has not been tampered with and that it has been provided by a trusted vendor. Self-signed certificates are disallowed by this requirement. Certificates used to verify the software must be from an approved Certificate Authority (CA).

identifiers:  CCE-26876-3

references:  CM-5(3), SI-7, MA-1(b), 1749, 366, Req-6.2, 5.10.4.1, 3.4.8

Remediation Shell script:   (show)

Complexity:low
Disruption:low
Strategy:disable
sed -i 's/gpgcheck=.*/gpgcheck=1/g' /etc/yum.repos.d/*

Ensure Software Patches Installed   [ref]rule

If the system is joined to the Red Hat Network, a Red Hat Satellite Server, or a yum server, run the following command to install updates:

$ sudo yum update
If the system is not configured to use one of these sources, updates (in the form of RPM packages) can be manually downloaded from the Red Hat Network and installed using rpm.

NOTE: U.S. Defense systems are required to be patched within 30 days or sooner as local policy dictates.

Rationale:

Installing software updates is a fundamental mitigation against the exploitation of publicly-known vulnerabilities. If the most recent security patches and updates are not installed, unauthorized users may take advantage of weaknesses in the unpatched software. The lack of prompt attention to patching could result in a system compromise.

identifiers:  CCE-26895-3

references:  SI-2, SI-2(c), MA-1(b), 366, Req-6.2, 1.7, SRG-OS-000480-GPOS-00227, RHEL-07-020260, 5.10.4.1

Remediation Shell script:   (show)

Complexity:low
Disruption:low
Strategy:disable
yum -y update

Ensure YUM Removes Previous Package Versions   [ref]rule

Yum should be configured to remove previous software components after previous versions have been installed. To configure yum to remove the previous software components after updating, set the clean_requirements_on_remove to 1 in /etc/yum.conf.

Rationale:

Previous versions of software components that are not removed from the information system after updates have been installed may be exploited by some adversaries.

identifiers:  CCE-80346-0

references:  SI-2(6), 2617, SRG-OS-000437-GPOS-00194, RHEL-07-020200, 3.4.8

Remediation Shell script:   (show)

Complexity:low
Disruption:low
Strategy:disable

if grep --silent ^clean_requirements_on_remove /etc/yum.conf ; then
        sed -i "s/^clean_requirements_on_remove.*/clean_requirements_on_remove=1/g" /etc/yum.conf
else
        echo -e "\n# Set clean_requirements_on_remove to 1 per security requirements" >> /etc/yum.conf
        echo "clean_requirements_on_remove=1" >> /etc/yum.conf
fi

Ensure gpgcheck Enabled for Local Packages   [ref]rule

Yum should be configured to verify the signature(s) of local packages prior to installation. To configure yum to verify signatures of local packages, set the localpkg_gpgcheck to 1 in /etc/yum.conf.

Rationale:

Changes to any software components can have significant effects to the overall security of the operating system. This requirement ensures the software has not been tampered and has been provided by a trusted vendor.

Accordingly, patches, service packs, device drivers, or operating system components must be signed with a certificate recognized and approved by the organization.

identifiers:  CCE-80347-8

references:  CM-5(3), 1749, SRG-OS-000366-GPOS-00153, RHEL-07-020060, 3.4.8

Remediation Shell script:   (show)

Complexity:low
Disruption:low
Strategy:disable

if grep --silent ^localpkg_gpgcheck /etc/yum.conf ; then
        sed -i "s/^localpkg_gpgcheck.*/localpkg_gpgcheck=1/g" /etc/yum.conf
else
        echo -e "\n# Set localpkg_gpgcheck to 1 per security requirements" >> /etc/yum.conf
        echo "localpkg_gpgcheck=1" >> /etc/yum.conf
fi

System and Software Integrity   [ref]group

System and software integrity can be gained by installing antivirus, increasing system encryption strength with FIPS, verifying installed software, enabling SELinux, installing an Intrusion Prevention System, etc. However, installing or enabling integrity checking tools cannot prevent intrusions, but they can detect that an intrusion may have occurred. Requirements for integrity checking may be highly dependent on the environment in which the system will be used. Snapshot-based approaches such as AIDE may induce considerable overhead in the presence of frequent software updates.

contains 19 rules

Software Integrity Checking   [ref]group

Both the AIDE (Advanced Intrusion Detection Environment) software and the RPM package management system provide mechanisms for verifying the integrity of installed software. AIDE uses snapshots of file metadata (such as hashes) and compares these to current system files in order to detect changes.

The RPM package management system can conduct integrity checks by comparing information in its metadata database with files installed on the system.

contains 9 rules

Verify Integrity with AIDE   [ref]group

AIDE conducts integrity checks by comparing information about files with previously-gathered information. Ideally, the AIDE database is created immediately after initial system configuration, and then again after any software update. AIDE is highly configurable, with further configuration information located in /usr/share/doc/aide-VERSION.

contains 7 rules

Install AIDE   [ref]rule

Install the AIDE package with the command:

$ sudo yum install aide

Rationale:

The AIDE package must be installed if it is to be available for integrity checking.

Remediation Shell script:   (show)

Complexity:low
Disruption:low
Strategy:enable

function package_command {

# Load function arguments into local variables
local package_operation=$1
local package=$2

# Check sanity of the input
if [ $# -ne "2" ]
then
  echo "Usage: package_command 'install/uninstall' 'rpm_package_name"
  echo "Aborting."
  exit 1
fi

# If dnf is installed, use dnf; otherwise, use yum
if [ -f "/usr/bin/dnf" ] ; then
  install_util="/usr/bin/dnf"
else
  install_util="/usr/bin/yum"
fi

if [ "$package_operation" != 'remove' ] ; then
  # If the rpm is not installed, install the rpm
  if ! /bin/rpm -q --quiet $package; then
    $install_util -y $package_operation $package
  fi
else
  # If the rpm is installed, uninstall the rpm
  if /bin/rpm -q --quiet $package; then
    $install_util -y $package_operation $package
  fi
fi

}

package_command install aide
Remediation Ansible snippet:   (show)

Complexity:low
Disruption:low
Strategy:enable
- name: Ensure aide is installed
  package:
    name="{{item}}"
    state=present
  with_items:
    - aide
Remediation Puppet snippet:   (show)

Complexity:low
Disruption:low
Strategy:enable
include install_aide

class install_aide {
  package { 'aide':
    ensure => 'installed',
  }
}
Remediation script:   (show)

Complexity:low
Disruption:low
Strategy:enable

package -add=aide

Build and Test AIDE Database   [ref]rule

Run the following command to generate a new database:

$ sudo /usr/sbin/aide --init
By default, the database will be written to the file /var/lib/aide/aide.db.new.gz. Storing the database, the configuration file /etc/aide.conf, and the binary /usr/sbin/aide (or hashes of these files), in a secure location (such as on read-only media) provides additional assurance about their integrity. The newly-generated database can be installed as follows:
$ sudo cp /var/lib/aide/aide.db.new.gz /var/lib/aide/aide.db.gz
To initiate a manual check, run the following command:
$ sudo /usr/sbin/aide --check
If this check produces any unexpected output, investigate.

Rationale:

For AIDE to be effective, an initial database of "known-good" information about files must be captured and it should be able to be verified against the installed files.

identifiers:  CCE-27220-3

references:  CM-3(d), CM-3(e), CM-6(d), CM-6(3), SC-28, SI-7, Req-11.5, 5.10.1.3

Remediation Shell script:   (show)

Complexity:low
Disruption:low
Strategy:disable
/usr/sbin/aide --init
/bin/cp -p /var/lib/aide/aide.db.new.gz /var/lib/aide/aide.db.gz

Configure Periodic Execution of AIDE   [ref]rule

At a minimum, AIDE should be configured to run a weekly scan. At most, AIDE should be run daily. To implement a daily execution of AIDE at 4:05am using cron, add the following line to /etc/crontab:

05 4 * * * root /usr/sbin/aide --check
To implement a weekly execution of AIDE at 4:05am using cron, add the following line to /etc/crontab:
05 4 * * 0 root /usr/sbin/aide --check
AIDE can be executed periodically through other means; this is merely one example.

Rationale:

By default, AIDE does not install itself for periodic execution. Periodically running AIDE is necessary to reveal unexpected changes in installed files.

Unauthorized changes to the baseline configuration could make the system vulnerable to various attacks or allow unauthorized access to the operating system. Changes to operating system configurations can have unintended side effects, some of which may be relevant to security.

Detecting such changes and providing an automated response can help avoid unintended, negative consequences that could ultimately affect the security state of the operating system. The operating system's Information Management Officer (IMO)/Information System Security Officer (ISSO) and System Administrators (SAs) must be notified via email and/or monitoring system trap when there is an unauthorized modification of a configuration item.

Remediation Shell script:   (show)

Complexity:low
Disruption:low
Strategy:disable
echo "05 4 * * * root /usr/sbin/aide --check" >> /etc/crontab

Configure Notification of Post-AIDE Scan Details   [ref]rule

AIDE should notify appropriate personnel of the details of a scan after the scan has been run. If AIDE has already been configured for periodic execution in /etc/crontab, append the following line to the existing AIDE line:

 | /bin/mail -s "$(hostname) - AIDE Integrity Check" root@localhost
Otherwise, add the following line to /etc/crontab:
05 4 * * * root /usr/sbin/aide --check | /bin/mail -s "$(hostname) - AIDE Integrity Check" root@localhost
AIDE can be executed periodically through other means; this is merely one example.

Rationale:

Unauthorized changes to the baseline configuration could make the system vulnerable to various attacks or allow unauthorized access to the operating system. Changes to operating system configurations can have unintended side effects, some of which may be relevant to security.

Detecting such changes and providing an automated response can help avoid unintended, negative consequences that could ultimately affect the security state of the operating system. The operating system's Information Management Officer (IMO)/Information System Security Officer (ISSO) and System Administrators (SAs) must be notified via email and/or monitoring system trap when there is an unauthorized modification of a configuration item.

identifiers:  CCE-80374-2

references:  CM-3(5), 1744, SRG-OS-000363-GPOS-00150, RHEL-07-020040

Configure AIDE to Verify Access Control Lists (ACLs)   [ref]rule

By default, the acl option is added to the FIPSR ruleset in AIDE. If using a custom ruleset or the acl option is missing, add acl to the appropriate ruleset. For example, add acl to the following line in /etc/aide.conf:

FIPSR = p+i+n+u+g+s+m+c+acl+selinux+xattrs+sha256
AIDE rules can be configured in multiple ways; this is merely one example that is already configured by default.

Rationale:

ACLs can provide permissions beyond those permitted through the file mode and must be verified by the file integrity tools.

identifiers:  CCE-80375-9

references:  SI-7.1, 366, SRG-OS-000480-GPOS-00227, RHEL-07-021600

Configure AIDE to Verify Extended Attributes   [ref]rule

By default, the xattrs option is added to the FIPSR ruleset in AIDE. If using a custom ruleset or the xattrs option is missing, add xattrs to the appropriate ruleset. For example, add xattrs to the following line in /etc/aide.conf:

FIPSR = p+i+n+u+g+s+m+c+acl+selinux+xattrs+sha256
AIDE rules can be configured in multiple ways; this is merely one example that is already configured by default.

Rationale:

Extended attributes in file systems are used to contain arbitrary data and file metadata with security implications.

identifiers:  CCE-80376-7

references:  SI-7.1, 366, SRG-OS-000480-GPOS-00227, RHEL-07-021610

Configure AIDE to Use FIPS 140-2 for Validating Hashes   [ref]rule

By default, the sha512 option is added to the NORMAL ruleset in AIDE. If using a custom ruleset or the sha512 option is missing, add sha512 to the appropriate ruleset. For example, add sha512 to the following line in /etc/aide.conf:

NORMAL = FIPSR+sha512
AIDE rules can be configured in multiple ways; this is merely one example that is already configured by default.

Rationale:

File integrity tools use cryptographic hashes for verifying file contents and directories have not been altered. These hashes must be FIPS 140-2 approved cryptographic hashes.

identifiers:  CCE-80377-5

references:  SI-7(1), 366, SRG-OS-000480-GPOS-00227, RHEL-07-021620, 3.13.11

Verify Integrity with RPM   [ref]group

The RPM package management system includes the ability to verify the integrity of installed packages by comparing the installed files with information about the files taken from the package metadata stored in the RPM database. Although an attacker could corrupt the RPM database (analogous to attacking the AIDE database as described above), this check can still reveal modification of important files. To list which files on the system differ from what is expected by the RPM database:

$ rpm -qVa
See the man page for rpm to see a complete explanation of each column.

contains 2 rules

Verify and Correct File Permissions with RPM   [ref]rule

Discretionary access control is weakened if a user or group has access permissions to system files and directories greater than the default. The RPM package management system can check file access permissions of installed software packages, including many that are important to system security. Verify that the file permissions, ownership, and gruop membership of system files and commands match vendor values. Check the file permissions, ownership, and group membership with the following command:

$ sudo rpm -Va | grep '^.M'
Output indicates files that do not match vendor defaults. After locating a file with incorrect permissions, run the following command to determine which package owns it:
$ rpm -qf FILENAME

Next, run the following command to reset its permissions to the correct values:
$ sudo rpm --setperms PACKAGENAME

warning  Note: Due to a bug in the gdm package, the RPM verify command may continue to fail even after file permissions have been correctly set on /var/log/gdm. This is being tracked in Red Hat Bugzilla #1275532.
Rationale:

Permissions on system binaries and configuration files that are too generous could allow an unauthorized user to gain privileges that they should not have. The permissions set by the vendor should be maintained. Any deviations from this baseline should be investigated.

Remediation Shell script:   (show)

Complexity:high
Disruption:medium
Strategy:restrict

# Declare array to hold list of RPM packages we need to correct permissions for
declare -a SETPERMS_RPM_LIST

# Create a list of files on the system having permissions different from what
# is expected by the RPM database
FILES_WITH_INCORRECT_PERMS=($(rpm -Va --nofiledigest | grep '^.M'))

# For each file path from that list:
# * Determine the RPM package the file path is shipped by,
# * Include it into SETPERMS_RPM_LIST array

for FILE_PATH in "${FILES_WITH_INCORRECT_PERMS[@]}"
do
	RPM_PACKAGE=$(rpm -qf "$FILE_PATH")
	SETPERMS_RPM_LIST=("${SETPERMS_RPM_LIST[@]}" "$RPM_PACKAGE")
done

# Remove duplicate mention of same RPM in $SETPERMS_RPM_LIST (if any)
SETPERMS_RPM_LIST=( $(echo "${SETPERMS_RPM_LIST[@]}" | sort -n | uniq) )

# For each of the RPM packages left in the list -- reset its permissions to the
# correct values
for RPM_PACKAGE in "${SETPERMS_RPM_LIST[@]}"
do
	rpm --setperms "${RPM_PACKAGE}"
done
Remediation Ansible snippet:   (show)

Complexity:high
Disruption:medium
Strategy:restrict

- name: "Read list of files with incorrect permissions"
  shell: "rpm -Va | grep '^.M' | sed -r 's;^.*\\s+(.+);\\1;g'"
  register: files_with_incorrect_permissions
  failed_when: False
  changed_when: False

- name: "Correct file permissions with RPM"
  shell: "rpm --setperms $(rpm -qf '{{item}}')"
  with_items: "{{ files_with_incorrect_permissions.stdout_lines }}"
  when: files_with_incorrect_permissions.stdout_lines | length > 0

Verify File Hashes with RPM   [ref]rule

Without cryptographic integrity protections, system executables and files can be altered by unauthorized users without detection. The RPM package management system can check the hashes of installed software packages, including many that are important to system security. To verify that the cryptographic hash of system files and commands match vendor values, run the following command to list which files on the system have hashes that differ from what is expected by the RPM database:

$ rpm -Va | grep '^..5'
A "c" in the second column indicates that a file is a configuration file, which may appropriately be expected to change. If the file was not expected to change, investigate the cause of the change using audit logs or other means. The package can then be reinstalled to restore the file. Run the following command to determine which package owns the file:
$ rpm -qf FILENAME
The package can be reinstalled from a yum repository using the command:
$ sudo yum reinstall PACKAGENAME
Alternatively, the package can be reinstalled from trusted media using the command:
$ sudo rpm -Uvh PACKAGENAME

Rationale:

The hashes of important files like system executables should match the information given by the RPM database. Executables with erroneous hashes could be a sign of nefarious activity on the system.

Remediation Ansible snippet:   (show)

Complexity:high
Disruption:medium

- name: "Set fact: Package manager reinstall command (dnf)"
  set_fact:
    package_manager_reinstall_cmd: dnf reinstall -y
  when: ansible_distribution == "Fedora"

- name: "Set fact: Package manager reinstall command (yum)"
  set_fact:
    package_manager_reinstall_cmd: yum reinstall -y
  when: ansible_distribution == "RedHat"

- name: "Read files with incorrect hash"
  shell: "rpm -Va | grep -E '^..5.* /(bin|sbin|lib|lib64|usr)/' | sed -r 's;^.*\\s+(.+);\\1;g'"
  register: files_with_incorrect_hash
  changed_when: False
  when: package_manager_reinstall_cmd is defined

- name: "Reinstall packages of files with incorrect hash"
  shell: "{{package_manager_reinstall_cmd}} $(rpm -qf '{{item}}')"
  with_items: "{{ files_with_incorrect_hash.stdout_lines }}"
  when: package_manager_reinstall_cmd is defined and (files_with_incorrect_hash.stdout_lines | length > 0)

Endpoint Protection Software   [ref]group

Endpoint protection security software that is not provided or supported by Red Hat can be installed to provide complementary or duplicative security capabilities to those provided by the base platform. Add-on software may not be appropriate for some specialized systems.

contains 6 rules

McAfee Endpoint Security Software   [ref]group

In DoD environments, McAfee Host-based Security System (HBSS) and VirusScan Enterprise for Linux (VSEL) is required to be installed on all systems.

contains 5 rules

McAfee Host-Based Intrusion Detection Software (HBSS)   [ref]group

McAfee Host-based Security System (HBSS) is a suite of software applications used to monitor, detect, and defend computer networks and systems.

contains 2 rules

Install the Asset Configuration Compliance Module (ACCM)   [ref]rule

Install the Asset Configuration Compliance Module (ACCM).

Rationale:

Without a host-based intrusion detection tool, there is no system-level defense when an intruder gains access to a system or network. Additionally, a host-based intrusion prevention tool can provide methods to immediately lock out detected intrusion attempts.

identifiers:  CCE-80126-6

references:  SC-7, SI-4(1).1, 366, 1263, Req-11.4, STG-OS-000480-GPOS-00227

Install the Policy Auditor (PA) Module   [ref]rule

Install the Policy Auditor (PA) Module.

Rationale:

Without a host-based intrusion detection tool, there is no system-level defense when an intruder gains access to a system or network. Additionally, a host-based intrusion prevention tool can provide methods to immediately lock out detected intrusion attempts.

identifiers:  CCE-80369-2

references:  SC-7, SI-4(1).1, 366, 1263, Req-11.4, STG-OS-000480-GPOS-00227

Install McAfee Virus Scanning Software   [ref]rule

Install McAfee VirusScan Enterprise for Linux antivirus software which is provided for DoD systems and uses signatures to search for the presence of viruses on the filesystem.

Rationale:

Virus scanning software can be used to detect if a system has been compromised by computer viruses, as well as to limit their spread to other systems.

identifiers:  CCE-80127-4

references:  SC-28, SI-3, SI-3(1)(ii), 366, 1239, 1668, SRG-OS-000480-GPOS-00227, RHEL-07-032000

Enable nails Service   [ref]rule

The nails service is used to run McAfee VirusScan Enterprise for Linux and McAfee Host-based Security System (HBSS) services. The nails service can be enabled with the following command:

$ sudo systemctl enable nails.service

Rationale:

Virus scanning software can be used to detect if a system has been compromised by computer viruses, as well as to limit their spread to other systems.

identifiers:  CCE-80128-2

references:  SC-28, SI-3, SI-3(1)(ii), 366, 1239, 1668, SRG-OS-000480-GPOS-00227

Virus Scanning Software Definitions Are Updated   [ref]rule

Ensure virus definition files are no older than 7 days or their last release.

Rationale:

Virus scanning software can be used to detect if a system has been compromised by computer viruses, as well as to limit their spread to other systems.

identifiers:  CCE-80129-0

references:  SC-28, SI-3, SI-3(1)(ii), 366, 1239, 1668, SRG-OS-000480-GPOS-00227, RHEL-07-032010

Install Intrusion Detection Software   [ref]rule

The base Red Hat platform already includes a sophisticated auditing system that can detect intruder activity, as well as SELinux, which provides host-based intrusion prevention capabilities by confining privileged programs and user sessions which may become compromised.

warning  Note in DoD environments, supplemental intrusion detection tools, such as the McAfee Host-based Security System, are available to integrate with existing infrastructure. When these supplemental tools interfere with proper functioning of SELinux, SELinux takes precedence.
Rationale:

Host-based intrusion detection tools provide a system-level defense when an intruder gains access to a system or network.

identifiers:  CCE-26818-5

references:  SC-7, 1263, Req-11.4

Federal Information Processing Standard (FIPS)   [ref]group

The Federal Information Processing Standard (FIPS) is a computer security standard which is developed by the U.S. Government and industry working groups to validate the quality of cryptographic modules. The FIPS standard provides four security levels to ensure adequate coverage of different industries, implementation of cryptographic modules, and organizational sizes and requirements.

FIPS 140-2 is the current standard for validating that mechanisms used to access cryptographic modules utilize authentication that meets industry and government requirements. For government systems, this allows Security Levels 1, 2, 3, or 4 for use on Red Hat Enterprise Linux.

See http://csrc.nist.gov/publications/PubsFIPS.html for more information.

contains 2 rules

Install the dracut-fips Package   [ref]rule

To enable FIPS, the system requires that the dracut-fips package be installed. The dracut-fips package can be installed with the following command:

$ sudo yum install dracut-fips

Rationale:

Use of weak or untested encryption algorithms undermines the purposes of utilizing encryption to protect data. The operating system must implement cryptographic modules adhering to the higher standards approved by the federal government since this provides assurance they have been tested and validated.

Enable FIPS Mode in GRUB2   [ref]rule

To ensure FIPS mode is enabled, rebuild initramfs by running the following command:

dracut -f
After the dracut command has been run, add the argument fips=1 to the default GRUB 2 command line for the Linux operating system in /etc/default/grub, in the manner below:
GRUB_CMDLINE_LINUX="crashkernel=auto rd.lvm.lv=VolGroup/LogVol06 rd.lvm.lv=VolGroup/lv_swap rhgb quiet rd.shell=0 fips=1"
Finally, rebuild the grub.cfg file by using the
grub2-mkconfig -o
command as follows:
  • On BIOS-based machines, issue the following command as root:
    ~]# grub2-mkconfig -o /boot/grub2/grub.cfg
  • On UEFI-based machines, issue the following command as root:
    ~]# grub2-mkconfig -o /boot/efi/EFI/redhat/grub.cfg

warning  Running
dracut -f
will overwrite the existing initramfs file.
warning  The system needs to be rebooted for these changes to take effect.
warning  The ability to enable FIPS does not denote FIPS compliancy or certification. Red Hat, Inc. and Red Hat Enterprise Linux are respectively FIPS certified and compliant. Community projects such as CentOS, Scientific Linux, etc. do not necessarily meet FIPS certification and compliancy. Therefore, non-certified vendors and/or projects do not meet this requirement even if technically feasible.

See http://csrc.nist.gov/groups/STM/cmvp/documents/140-1/1401vend.htm for a list of FIPS certified vendors.
Rationale:

Use of weak or untested encryption algorithms undermines the purposes of utilizing encryption to protect data. The operating system must implement cryptographic modules adhering to the higher standards approved by the federal government since this provides assurance they have been tested and validated.

Remediation Shell script:   (show)

Complexity:low
Disruption:low
Strategy:disable

if grep --silent ^PRELINKING /etc/sysconfig/prelink ; then
        sed -i "s/^PRELINKING.*/PRELINKING=yes/g" /etc/sysconfig/prelink
else
        echo -e "\n# Set PRELINKING to 'yes' per security requirements" >> /etc/sysconfig/prelink
        echo "PRELINKING=yes" >> /etc/sysconfig/prelink
fi

prelink -u -a

dracut -f

if [ -e /sys/firmware/efi ]; then
	BOOT=`df /boot/efi | tail -1 | awk '{print $1 }'`
else
	BOOT=`df /boot | tail -1 | awk '{ print $1 }'`
fi

/sbin/grubby --update-kernel=ALL --args="boot=${BOOT} fips=1"

Operating System Vendor Support and Certification   [ref]group

The assurance of a vendor to provide operating system support and maintenance for their product is an important criterion to ensure product stability and security over the life of the product. A certified product that follows the necessary standards and government certification requirements guarantees that known software vulnerabilities will be remediated, and proper guidance for protecting and securing the operating system will be given.

contains 1 rule

The Installed Operating System Is Vendor Supported and Certified   [ref]rule

The installed operating system must be maintained and certified by a vendor. Red Hat Enterprise Linux is supported by Red Hat, Inc. As the Red Hat Enterprise Linux vendor, Red Hat, Inc. is responsible for providing security patches as well as meeting and maintaining goverment certifications and standards.

Rationale:

An operating system is considered "supported" if the vendor continues to provide security patches for the product as well as maintain government certification requirements. With an unsupported release, it will not be possible to resolve security issue discovered in the system software as well as meet government certifications.

identifiers:  CCE-80349-4

references:  SI-2(c), 366, RHEL-07-020250, SRG-OS-000480-GPOS-00227

GNOME Desktop Environment   [ref]group

GNOME is a graphical desktop environment bundled with many Linux distributions that allow users to easily interact with the operating system graphically rather than textually. The GNOME Graphical Display Manager (GDM) provides login, logout, and user switching contexts as well as display server management.

GNOME is developed by the GNOME Project and is considered the default Red Hat Graphical environment.

For more information on GNOME and the GNOME Project, see https://www.gnome.org

contains 24 rules
contains 6 rules

Disable the GNOME3 Login User List   [ref]rule

In the default graphical environment, users logging directly into the system are greeted with a login screen that displays all known users. This functionality should be disabled by setting disable-user-list to true.

To disable, add or edit disable-user-list to /etc/dconf/db/gdm.d/00-security-settings. For example:

[org/gnome/login-screen]
disable-user-list=true
Once the setting has been added, add a lock to /etc/dconf/db/gdm.d/locks/00-security-settings-lock to prevent user modification. For example:
/org/gnome/login-screen/disable-user-list
After the settings have been set, run dconf update.

Rationale:

Leaving the user list enabled is a security risk since it allows anyone with physical access to the system to quickly enumerate known user accounts without logging in.

identifiers:  CCE-80106-8

references:  AC-23

Disable the GNOME3 Login Restart and Shutdown Buttons   [ref]rule

In the default graphical environment, users logging directly into the system are greeted with a login screen that allows any user, known or unknown, the ability the ability to shutdown or restart the system. This functionality should be disabled by setting disable-restart-buttons to true.

To disable, add or edit disable-restart-buttons to /etc/dconf/db/gdm.d/00-security-settings. For example:

[org/gnome/login-screen]
disable-restart-buttons=true
Once the setting has been added, add a lock to /etc/dconf/db/gdm.d/locks/00-security-settings-lock to prevent user modification. For example:
/org/gnome/login-screen/disable-restart-buttons
After the settings have been set, run dconf update.

Rationale:

A user who is at the console can reboot the system at the login screen. If restart or shutdown buttons are pressed at the login screen, this can create the risk of short-term loss of availability of systems due to reboot.

identifiers:  CCE-80107-6

references:  AC-6, 366, SRG-OS-000480-GPOS-00227, RHEL-07-TBD, 3.1.2

Enable the GNOME3 Login Smartcard Authentication   [ref]rule

In the default graphical environment, smart card authentication can be enabled on the login screen by setting enable-smartcard-authentication to true.

To enable, add or edit enable-smartcard-authentication to /etc/dconf/db/gdm.d/00-security-settings. For example:

[org/gnome/login-screen]
enable-smartcard-authentication=true
Once the setting has been added, add a lock to /etc/dconf/db/gdm.d/locks/00-security-settings-lock to prevent user modification. For example:
/org/gnome/login-screen/enable-smartcard-authentication
After the settings have been set, run dconf update.

Rationale:

Smart card login provides two-factor authentication stronger than that provided by a username and password combination. Smart cards leverage PKI (public key infrastructure) in order to provide and verify credentials.

identifiers:  CCE-80108-4

references:  765, 766, 767, 768, 771, 772, 884, Req-8.3

Configure GNOME Screen Locking   [ref]group

In the default GNOME3 desktop, the screen can be locked by selecting the user name in the far right corner of the main panel and selecting Lock.

The following sections detail commands to enforce idle activation of the screensaver, screen locking, a blank-screen screensaver, and an idle activation time.

Because users should be trained to lock the screen when they step away from the computer, the automatic locking feature is only meant as a backup.

The root account can be screen-locked; however, the root account should never be used to log into an X Windows environment and should only be used to for direct login via console in emergency circumstances.

For more information about enforcing preferences in the GNOME3 environment using the DConf configuration system, see http://wiki.gnome.org/dconf and the man page dconf(1). For Red Hat specific information on configuring DConf settings, see https://access.redhat.com/documentation/en-US/Red_Hat_Enterprise_Linux/7/html/Desktop_Migration_and_Administration_Guide/part-Configuration_and_Administration.html

contains 7 rules

Set GNOME3 Screensaver Inactivity Timeout   [ref]rule

The idle time-out value for inactivity in the GNOME3 desktop is configured via the idle-delay setting must be set under an appropriate configuration file(s) in the /etc/dconf/db/local.d directory and locked in /etc/dconf/db/local.d/locks directory to prevent user modification.

For example, to configure the system for a 15 minute delay, add the following to /etc/dconf/db/local.d/00-security-settings:

[org/gnome/desktop/session]
idle-delay='uint32 900'
Once the setting has been added, add a lock to /etc/dconf/db/local.d/locks/00-security-settings-lock to prevent user modification. For example:
/org/gnome/desktop/session/idle-delay
After the settings have been set, run dconf update.

Rationale:

A session time-out lock is a temporary action taken when a user stops work and moves away from the immediate physical vicinity of the information system but does not logout because of the temporary nature of the absence. Rather than relying on the user to manually lock their operating system session prior to vacating the vicinity, GNOME3 can be configured to identify when a user's session has idled and take action to initiate a session lock.

identifiers:  CCE-80110-0

references:  AC-11(a), 57, Req-8.1.8, SRG-OS-000029-GPOS-00010, RHEL-07-010070, 5.5.5, 3.1.10

Remediation Shell script:   (show)

Complexity:low
Disruption:low
Strategy:disable

inactivity_timeout_value="900"

# Define constants to be reused below
ORG_GNOME_DESKTOP_SESSION="org/gnome/desktop/session"
SSG_DCONF_IDLE_DELAY_FILE="/etc/dconf/db/local.d/10-scap-security-guide"
SESSION_LOCKS_FILE="/etc/dconf/db/local.d/locks/session"
IDLE_DELAY_DEFINED="FALSE"

# First update '[org/gnome/desktop/session] idle-delay' settings in
# /etc/dconf/db/local.d/* if already defined
for FILE in /etc/dconf/db/local.d/*
do
	if grep -q -d skip "$ORG_GNOME_DESKTOP_SESSION" "$FILE"
	then
		if grep 'idle-delay' "$FILE"
		then
			sed -i "s/idle-delay=.*/idle-delay=uint32 ${inactivity_timeout_value}/g" "$FILE"
			IDLE_DELAY_DEFINED="TRUE"
		fi
	fi
done

# Then define '[org/gnome/desktop/session] idle-delay' setting
# if still not defined yet
if [ "$IDLE_DELAY_DEFINED" != "TRUE" ]
then
	echo "" >> $SSG_DCONF_IDLE_DELAY_FILE
	echo "[org/gnome/desktop/session]" >>  $SSG_DCONF_IDLE_DELAY_FILE
	echo "idle-delay=uint32 ${inactivity_timeout_value}" >> $SSG_DCONF_IDLE_DELAY_FILE
fi

# Verify if 'idle-delay' modification is locked. If not, lock it
if ! grep -q "^/${ORG_GNOME_DESKTOP_SESSION}/idle-delay$" /etc/dconf/db/local.d/locks/*
then
	# Check if "$SESSION_LOCK_FILE" exists. If not, create it.
	if [ ! -f "$SESSION_LOCKS_FILE" ]
	then
		touch "$SESSION_LOCKS_FILE"
	fi
	echo "/${ORG_GNOME_DESKTOP_SESSION}/idle-delay" >> "$SESSION_LOCKS_FILE"
fi

Enable GNOME3 Screensaver Idle Activation   [ref]rule

To activate the screensaver in the GNOME3 desktop after a period of inactivity, add or set idle-activation-enabled to true in /etc/dconf/db/local.d/00-security-settings. For example:

[org/gnome/desktop/screensaver]
idle_activation_enabled=true
Once the setting has been added, add a lock to /etc/dconf/db/local.d/locks/00-security-settings-lock to prevent user modification. For example:
/org/gnome/desktop/screensaver/idle-activation-enabled
After the settings have been set, run dconf update.

Rationale:

A session time-out lock is a temporary action taken when a user stops work and moves away from the immediate physical vicinity of the information system but does not logout because of the temporary nature of the absence. Rather than relying on the user to manually lock their operating system session prior to vacating the vicinity, GNOME desktops can be configured to identify when a user's session has idled and take action to initiate the session lock.

Enabling idle activation of the screensaver ensures the screensaver will be activated after the idle delay. Applications requiring continuous, real-time screen display (such as network management products) require the login session does not have administrator rights and the display station is located in a controlled-access area.

identifiers:  CCE-80111-8

references:  AC-11(a), 57, SRG-OS-000029-GPOS-00010, RHEL-07-010100, Req-8.1.8, 5.5.5, 3.1.10

Remediation Shell script:   (show)

Complexity:low
Disruption:low
Strategy:disable

# Define constants to be reused below
ORG_GNOME_DESKTOP_SCREENSAVER="org/gnome/desktop/screensaver"
SSG_DCONF_IDLE_ACTIVATION_FILE="/etc/dconf/db/local.d/10-scap-security-guide"
SCREENSAVER_LOCKS_FILE="/etc/dconf/db/local.d/locks/screensaver"
IDLE_ACTIVATION_DEFINED="FALSE"

# First update '[org/gnome/desktop/screensaver] idle-activation-enabled' settings in
# /etc/dconf/db/local.d/* if already defined
for FILE in /etc/dconf/db/local.d/*
do
	if grep -q -d skip "$ORG_GNOME_DESKTOP_SCREENSAVER" "$FILE"
	then
		if grep 'idle-activation-enabled' "$FILE"
		then
			sed -i "s/idle-activation-enabled=.*/idle-activation-enabled=true/g" "$FILE"
			IDLE_ACTIVATION_DEFINED="TRUE"
		fi
	fi
done

# Then define '[org/gnome/desktop/screensaver] idle-activation-enabled' setting
# if still not defined yet
if [ "$IDLE_ACTIVATION_DEFINED" != "TRUE" ]
then
	echo "" >> $SSG_DCONF_IDLE_ACTIVATION_FILE
	echo "[org/gnome/desktop/screensaver]" >>  $SSG_DCONF_IDLE_ACTIVATION_FILE
	echo "idle-activation-enabled=true" >> $SSG_DCONF_IDLE_ACTIVATION_FILE
fi

# Verify if 'idle-activation-enabled' modification is locked. If not, lock it
if ! grep -q "^/${ORG_GNOME_DESKTOP_SCREENSAVER}/idle-activation-enabled$" /etc/dconf/db/local.d/locks/*
then
	# Check if "$SCREENSAVER_LOCK_FILE" exists. If not, create it.
	if [ ! -f "$SCREENSAVER_LOCKS_FILE" ]
	then
		touch "$SCREENSAVER_LOCKS_FILE"
	fi
	echo "/${ORG_GNOME_DESKTOP_SCREENSAVER}/idle-activation-enabled" >> "$SCREENSAVER_LOCKS_FILE"
fi

Enable GNOME3 Screensaver Lock After Idle Period   [ref]rule

To activate locking of the screensaver in the GNOME3 desktop when it is activated, add or set lock-enabled to true in /etc/dconf/db/local.d/00-security-settings. For example:

[org/gnome/desktop/screensaver]
lock-enabled=true
Once the settings have been added, add a lock to /etc/dconf/db/local.d/locks/00-security-settings-lock to prevent user modification. For example:
/org/gnome/desktop/screensaver/lock-enabled
After the settings have been set, run dconf update.

Rationale:

A session lock is a temporary action taken when a user stops work and moves away from the immediate physical vicinity of the information system but does not want to logout because of the temporary nature of the absense.

Remediation Shell script:   (show)

Complexity:low
Disruption:low
Strategy:disable

# Define constants to be reused below
ORG_GNOME_DESKTOP_SCREENSAVER="org/gnome/desktop/screensaver"
SSG_DCONF_LOCK_ENABLED_FILE="/etc/dconf/db/local.d/10-scap-security-guide"
SCREENSAVER_LOCKS_FILE="/etc/dconf/db/local.d/locks/screensaver"
LOCK_ENABLED_DEFINED="FALSE"
LOCK_DELAY_DEFINED="FALSE"

# First update '[org/gnome/desktop/screensaver] lock-enabled' and
# '[org/gnome/desktop/screensaver] lock-delay' settings in
# /etc/dconf/db/local.d/* if already defined
for FILE in /etc/dconf/db/local.d/*
do
	if grep -q -d skip "$ORG_GNOME_DESKTOP_SCREENSAVER" "$FILE"
	then
		if grep 'lock-enabled' "$FILE"
		then
			sed -i "s/lock-enabled=.*/lock-enabled=true/g" "$FILE"
			LOCK_ENABLED_DEFINED="TRUE"
		fi
		if grep 'lock-delay' "$FILE"
		then
			sed -i "s/lock-delay=.*/lock-delay=uint32 0/g" "$FILE"
			LOCK_DELAY_DEFINED="TRUE"
		fi
	fi
done

# Then define '[org/gnome/desktop/screensaver] lock-enabled' setting
# if still not defined yet
if [ "$LOCK_ENABLED_DEFINED" != "TRUE" ] || [ "$LOCK_DELAY_DEFINED" != "TRUE" ]
then
	echo "" >> $SSG_DCONF_LOCK_ENABLED_FILE
	echo "[org/gnome/desktop/screensaver]" >>  $SSG_DCONF_LOCK_ENABLED_FILE
	echo "lock-enabled=true" >> $SSG_DCONF_LOCK_ENABLED_FILE
	echo "lock-delay=uint32 0" >> $SSG_DCONF_LOCK_ENABLED_FILE
fi

# Verify if 'lock-enabled' modification is locked. If not, lock it
if ! grep -q "^/${ORG_GNOME_DESKTOP_SCREENSAVER}/lock-enabled$" /etc/dconf/db/local.d/locks/*
then
	# Check if "$SCREENSAVER_LOCK_FILE" exists. If not, create it.
	if [ ! -f "$SCREENSAVER_LOCKS_FILE" ]
	then
		touch "$SCREENSAVER_LOCKS_FILE"
	fi
	echo "/${ORG_GNOME_DESKTOP_SCREENSAVER}/lock-enabled" >> "$SCREENSAVER_LOCKS_FILE"
fi


# Verify if 'lock-delay' modification is locked. If not, lock it
if ! grep -q "^/${ORG_GNOME_DESKTOP_SCREENSAVER}/lock-delay$" /etc/dconf/db/local.d/locks/*
then
        # Check if "$SCREENSAVER_LOCK_FILE" exists. If not, create it.
        if [ ! -f "$SCREENSAVER_LOCKS_FILE" ]
        then
                touch "$SCREENSAVER_LOCKS_FILE"
        fi
        echo "/${ORG_GNOME_DESKTOP_SCREENSAVER}/lock-delay" >> "$SCREENSAVER_LOCKS_FILE"
fi

Set GNOME3 Screensaver Lock Delay After Activation Period   [ref]rule

To activate the locking delay of the screensaver in the GNOME3 desktop when the screensaver is activated, add or set lock-delay to uint32 0 in /etc/dconf/db/local.d/00-security-settings. For example:

[org/gnome/desktop/screensaver]
lock-delay=uint32 0
Once the setting has been added, add a lock to /etc/dconf/db/local.d/locks/00-security-settings-lock to prevent user modification. For example:
/org/gnome/desktop/screensaver/lock-delay
After the settings have been set, run dconf update.

Rationale:

A session lock is a temporary action taken when a user stops work and moves away from the immediate physical vicinity of the information system but does not want to logout because of the temporary nature of the absense.

identifiers:  CCE-80370-0

references:  AC-11(a), 56, Req-8.1.8, OS-SRG-000029-GPOS-00010, RHEL-07-010110, 3.1.10

Implement Blank Screensaver   [ref]rule

To set the screensaver mode in the GNOME3 desktop to a blank screen, add or set picture-uri to string '' in /etc/dconf/db/local.d/00-security-settings. For example:

[org/gnome/desktop/screensaver]
picture-uri=string ''
Once the settings have been added, add a lock to /etc/dconf/db/local.d/locks/00-security-settings-lock to prevent user modification. For example:
/org/gnome/desktop/screensaver/picture-uri
After the settings have been set, run dconf update.

Rationale:

Setting the screensaver mode to blank-only conceals the contents of the display from passersby.

identifiers:  CCE-80113-4

references:  AC-11(b), 60, Req-8.1.8, 5.5.5, 3.1.10

Remediation Shell script:   (show)

Complexity:low
Disruption:low
Strategy:disable

# Define constants to be reused below
ORG_GNOME_DESKTOP_SCREENSAVER="org/gnome/desktop/screensaver"
SSG_DCONF_MODE_BLANK_FILE="/etc/dconf/db/local.d/10-scap-security-guide"
SCREENSAVER_LOCKS_FILE="/etc/dconf/db/local.d/locks/screensaver"
MODE_BLANK_DEFINED="FALSE"

# First update '[org/gnome/desktop/screensaver] picture-uri' settings in
# /etc/dconf/db/local.d/* if already defined
for FILE in /etc/dconf/db/local.d/*
do
	if grep -q -d skip "$ORG_GNOME_DESKTOP_SCREENSAVER" "$FILE"
	then
		if grep 'picture-uri' "$FILE"
		then
			sed -i "s/picture-uri=.*/picture-uri=string ''/g" "$FILE"
			MODE_BLANK_DEFINED="TRUE"
		fi
	fi
done

# Then define '[org/gnome/desktop/screensaver] picture-uri' setting
# if still not defined yet
if [ "$MODE_BLANK_DEFINED" != "TRUE" ]
then
	echo "" >> $SSG_DCONF_MODE_BLANK_FILE
	echo "[org/gnome/desktop/screensaver]" >>  $SSG_DCONF_MODE_BLANK_FILE
	echo "picture-uri=string ''" >> $SSG_DCONF_MODE_BLANK_FILE
fi

# Verify if 'picture-uri' modification is locked. If not, lock it
if ! grep -q "^/${ORG_GNOME_DESKTOP_SCREENSAVER}/picture-uri$" /etc/dconf/db/local.d/locks/*
then
	# Check if "$SCREENSAVER_LOCK_FILE" exists. If not, create it.
	if [ ! -f "$SCREENSAVER_LOCKS_FILE" ]
	then
		touch "$SCREENSAVER_LOCKS_FILE"
	fi
	echo "/${ORG_GNOME_DESKTOP_SCREENSAVER}/picture-uri" >> "$SCREENSAVER_LOCKS_FILE"
fi

Ensure Users Cannot Change GNOME3 Session Settings   [ref]rule

If not already configured, ensure that users cannot change GNOME3 session idle and lock settings by adding /org/gnome/desktop/screensaver/lock-delay and /org/gnome/desktop/session/idle-delay to /etc/dconf/db/local.d/locks/00-security-settings-lock to prevent user modification. For example:

/org/gnome/desktop/screensaver/lock-delay
/org/gnome/desktop/session/idle-delay
After the settings have been set, run dconf update.

Rationale:

A session time-out lock is a temporary action taken when a user stops work and moves away from the immediate physical vicinity of the information system but does not logout because of the temporary nature of the absence. Rather than relying on the user to manually lock their operating system session prior to vacating the vicinity, GNOME desktops can be configured to identify when a user's session has idled and take action to initiate the session lock. As such, users should not be allowed to change session settings.

identifiers:  CCE-80371-8

references:  AC-11(a), 57, SRG-OS-00029-GPOS-0010, RHEL-07-010081, 3.1.10

GNOME System Settings   [ref]group

GNOME provides configuration and functionality to a graphical desktop environment that changes grahical configurations or allow a user to perform actions that users normally would not be able to do in non-graphical mode such as remote access configuration, power policies, Geo-location, etc. Configuring such settings in GNOME will prevent accidential graphical configuration changes by users from taking place.

contains 4 rules

Disable Ctrl-Alt-Del Reboot Key Sequence in GNOME3   [ref]rule

By default, GNOME will reboot the system if the Ctrl-Alt-Del key sequence is pressed.

To configure the system to ignore the Ctrl-Alt-Del key sequence from the Graphical User Interface (GUI) instead of rebooting the system, add or set logout to string '' in /etc/dconf/db/local.d/00-security-settings. For example:

[org/gnome/settings-daemon/plugins/media-keys]
logout=string ''
Once the settings have been added, add a lock to /etc/dconf/db/local.d/locks/00-security-settings-lock to prevent user modification. For example:
/org/gnome/settings-daemon/plugins/media-keys/logout
After the settings have been set, run dconf update.

Rationale:

A locally logged-in user who presses Ctrl-Alt-Del, when at the console, can reboot the system. If accidentally pressed, as could happen in the case of mixed OS environment, this can create the risk of short-term loss of availability of systems due to unintentional reboot.

identifiers:  CCE-80124-1

references:  AC-6, 366, SRG-OS-000480-GPOS-00227, RHEL-07-TBD, 3.1.2

Disable User Administration in GNOME3   [ref]rule

By default, GNOME will allow all users to have some administratrion capability. This should be disabled so that non-administrative users are not making configuration changes. To configure the system to disable user administration capability in the Graphical User Interface (GUI), add or set user-administration-disabled to true in /etc/dconf/db/local.d/00-security-settings. For example:

[org/gnome/desktop/lockdown]
user-administration-disabled=true
Once the settings have been added, add a lock to /etc/dconf/db/local.d/locks/00-security-settings-lock to prevent user modification. For example:
/org/gnome/desktop/lockdown/user-administration-disabled
After the settings have been set, run dconf update.

Rationale:

Allowing all users to have some administratrive capabilities to the system through the Graphical User Interface (GUI) when they would not have them otherwise could allow unintended configuration changes as well as a nefarious user the capability to make system changes such as adding new accounts, etc.

identifiers:  CCE-80115-9

references:  3.1.5

Disable Power Settings in GNOME3   [ref]rule

By default, GNOME enables a power profile designed for mobile devices with battery usage. While useful for mobile devices, this setting should be disabled for all other systems. To configure the system to disable the power setting, add or set active to false in /etc/dconf/db/local.d/00-security-settings. For example:

[org/gnome/settings-daemon/plugins/power]
active=false
Once the settings have been added, add a lock to /etc/dconf/db/local.d/locks/00-security-settings-lock to prevent user modification. For example:
/org/gnome/settings-daemon/plugins/power
After the settings have been set, run dconf update.

Rationale:

Power settings should not be enabled on systems that are not mobile devices. Enabling power settings on non-mobile devices could have unintended processing consequences on standard systems.

identifiers:  CCE-80116-7

Disable Geolocation in GNOME3   [ref]rule

GNOME allows the clock and applications to track and access location information. This setting should be disabled as applications should not track system location. To configure the system to disable location tracking, add or set enabled to false in /etc/dconf/db/local.d/00-security-settings. For example:

[org/gnome/system/location]
enabled=false
To configure the clock to disable location tracking, add or set geolocation to false in /etc/dconf/db/local.d/00-security-settings. For example:
[org/gnome/clocks]
geolocation=false
Once the settings have been added, add a lock to /etc/dconf/db/local.d/locks/00-security-settings-lock to prevent user modification. For example:
/org/gnome/system/location/enabled
/org/gnome/clocks/geolocation
After the settings have been set, run dconf update.

Rationale:

Power settings should not be enabled on systems that are not mobile devices. Enabling power settings on non-mobile devices could have unintended processing consequences on standard systems.

identifiers:  CCE-80117-5

GNOME Network Settings   [ref]group

GNOME network settings that apply to the graphical interface.

contains 2 rules

Disable WIFI Network Connection Creation in GNOME3   [ref]rule

GNOME allows users to create ad-hoc wireless connections through the NetworkManager applet. Wireless connections should be disabled by adding or setting disable-wifi-create to true in /etc/dconf/db/local.d/00-security-settings. For example:

[org/gnome/nm-applet]
disable-wifi-create=true
Once the settings have been added, add a lock to /etc/dconf/db/local.d/locks/00-security-settings-lock to prevent user modification. For example:
/org/gnome/nm-applet/disable-wifi-create
After the settings have been set, run dconf update.

Rationale:

Wireless network connections should not be allowed to be configured by general users on a given system as it could open the system to backdoor attacks.

identifiers:  CCE-80118-3

references:  3.1.16

Disable WIFI Network Notification in GNOME3   [ref]rule

By default, GNOME disables WIFI notification. This should be permanently set so that users do not connect to a wireless network when the system finds one. While useful for mobile devices, this setting should be disabled for all other systems. To configure the system to disable the WIFI notication, add or set suppress-wireless-networks-available to true in /etc/dconf/db/local.d/00-security-settings. For example:

[org/gnome/nm-applet]
suppress-wireless-networks-available=true
Once the settings have been added, add a lock to /etc/dconf/db/local.d/locks/00-security-settings-lock to prevent user modification. For example:
/org/gnome/nm-applet/suppress-wireless-networks-available
After the settings have been set, run dconf update.

Rationale:

Wireless network connections should not be allowed to be configured by general users on a given system as it could open the system to backdoor attacks.

identifiers:  CCE-80119-1

references:  3.1.16

GNOME Remote Access Settings   [ref]group

GNOME remote access settings that apply to the graphical interface.

contains 2 rules

Require Credential Prompting for Remote Access in GNOME3   [ref]rule

By default, GNOME does not require credentials when using Vino for remote access. To configure the system to require remote credentials, add or set authentication-methods to ['vnc'] in /etc/dconf/db/local.d/00-security-settings. For example:

[org/gnome/Vino]
authentication-methods=['vnc']
Once the settings have been added, add a lock to /etc/dconf/db/local.d/locks/00-security-settings-lock to prevent user modification. For example:
/org/gnome/Vino/authentication-methods
After the settings have been set, run dconf update.

Rationale:

Username and password prompting is required for remote access. Otherwise, non-authorized and nefarious users can access the system freely.

identifiers:  CCE-80120-9

references:  3.1.12

Require Encryption for Remote Access in GNOME3   [ref]rule

By default, GNOME requires encryption when using Vino for remote access. To prevent remote access encryption from being disabled, add or set require-encryption to true in /etc/dconf/db/local.d/00-security-settings. For example:

[org/gnome/Vino]
require-encryption=true
Once the settings have been added, add a lock to /etc/dconf/db/local.d/locks/00-security-settings-lock to prevent user modification. For example:
/org/gnome/Vino/require-encryption
After the settings have been set, run dconf update.

Rationale:

Open X displays allow an attacker to capture keystrokes and to execute commands remotely.

identifiers:  CCE-80121-7

references:  CM-2(1)(b), 366, SRG-OS-000480-GPOS-00227, RHEL-07-TBD, 3.1.13

GNOME Media Settings   [ref]group

GNOME media settings that apply to the graphical interface.

contains 2 rules

Disable GNOME3 Automounting   [ref]rule

The system's default desktop environment, GNOME3, will mount devices and removable media (such as DVDs, CDs and USB flash drives) whenever they are inserted into the system. To disable automount and autorun within GNOME3, add or set automount to false, automount-open to false, and autorun-never to true in /etc/dconf/db/local.d/00-security-settings. For example:

[org/gnome/desktop/media-handling]
automount=false
automount-open=false
autorun-never=true
Once the settings have been added, add a lock to /etc/dconf/db/local.d/locks/00-security-settings-lock to prevent user modification. For example:
/org/gnome/desktop/media-handling/automount
/org/gnome/desktop/media-handling/auto-open
/org/gnome/desktop/media-handling/autorun-never
After the settings have been set, run dconf update.

Rationale:

Disabling automatic mounting in GNOME3 can prevent the introduction of malware via removable media. It will, however, also prevent desktop users from legitimate use of removable media.

identifiers:  CCE-80122-5

references:  AC-19(a), AC-19(d), AC-19(e), 3.1.7

Disable All GNOME3 Thumbnailers   [ref]rule

The system's default desktop environment, GNOME3, uses a number of different thumbnailer programs to generate thumbnails for any new or modified content in an opened folder. To disable the execution of these thumbnail applications, add or set disable-all to true in /etc/dconf/db/local.d/00-security-settings. For example:

[org/gnome/desktop/thumbnailers]
disable-all=true
Once the settings have been added, add a lock to /etc/dconf/db/local.d/locks/00-security-settings-lock to prevent user modification. For example:
/org/gnome/desktop/thumbnailers/disable-all
After the settings have been set, run dconf update. This effectively prevents an attacker from gaining access to a system through a flaw in GNOME3's Nautilus thumbnail creators.

Rationale:

An attacker with knowledge of a flaw in a GNOME3 thumbnailer application could craft a malicious file to exploit this flaw. Assuming the attacker could place the malicious file on the local filesystem (via a web upload for example) and assuming a user browses the same location using Nautilus, the malicious file would exploit the thumbnailer with the potential for malicious code execution. It is best to disable these thumbnailer applications unless they are explicitly required.

identifiers:  CCE-80123-3

references:  CM-7

Sudo   [ref]group

Sudo, which stands for "su 'do'", provides the ability to delegate authority to certain users, groups of users, or system administrators. When configured for system users and/or groups, Sudo can allow a user or group to execute privileged commands that normally only root is allowed to execute.

For more information on Sudo and addition Sudo configuration options, see https://www.sudo.ws

contains 2 rules

Ensure Users Re-Authenticate for Privilege Escalation - sudo NOPASSWD   [ref]rule

The sudo NOPASSWD tag, when specified, allows a user to execute commands using sudo without having to authenticate. This should be disabled by making sure that the NOPASSWD tag does not exist in /etc/sudoers configuration file or any sudo configuration snippets in /etc/sudoers.d/.

Rationale:

Without re-authentication, users may access resources or perform tasks for which they do not have authorization.

When operating systems provide the capability to escalate a functional capability, it is critical that the user re-authenticate.

Ensure Users Re-Authenticate for Privilege Escalation - sudo !authenticate   [ref]rule

The sudo !authenticate option, when specified, allows a user to execute commands using sudo without having to authenticate. This should be disabled by making sure that the !authenticate option does not exist in /etc/sudoers configuration file or any sudo configuration snippets in /etc/sudoers.d/.

Rationale:

Without re-authentication, users may access resources or perform tasks for which they do not have authorization.

When operating systems provide the capability to escalate a functional capability, it is critical that the user re-authenticate.

File Permissions and Masks   [ref]group

Traditional Unix security relies heavily on file and directory permissions to prevent unauthorized users from reading or modifying files to which they should not have access.

Several of the commands in this section search filesystems for files or directories with certain characteristics, and are intended to be run on every local partition on a given system. When the variable PART appears in one of the commands below, it means that the command is intended to be run repeatedly, with the name of each local partition substituted for PART in turn.

The following command prints a list of all xfs partitions on the local system, which is the default filesystem for Red Hat Enterprise Linux 7 installations:

$ mount -t xfs | awk '{print $3}'
For any systems that use a different local filesystem type, modify this command as appropriate.

contains 17 rules

Restrict Partition Mount Options   [ref]group

System partitions can be mounted with certain options that limit what files on those partitions can do. These options are set in the /etc/fstab configuration file, and can be used to make certain types of malicious behavior more difficult.

contains 3 rules

Add nodev Option to Removable Media Partitions   [ref]rule

The nodev mount option prevents files from being interpreted as character or block devices. Legitimate character and block devices should exist only in the /dev directory on the root partition or within chroot jails built for system services. Add the nodev option to the fourth column of /etc/fstab for the line which controls mounting of any removable media partitions.

Rationale:

The only legitimate location for device files is the /dev directory located on the root partition. An exception to this is chroot jails, and it is not advised to set nodev on partitions which contain their root filesystems.

identifiers:  CCE-80146-4

references:  AC-19(a), AC-19(d), AC-19(e), CM-7, MP-2

Add noexec Option to Removable Media Partitions   [ref]rule

The noexec mount option prevents the direct execution of binaries on the mounted filesystem. Preventing the direct execution of binaries from removable media (such as a USB key) provides a defense against malicious software that may be present on such untrusted media. Add the noexec option to the fourth column of /etc/fstab for the line which controls mounting of any removable media partitions.

Rationale:

Allowing users to execute binaries from removable media such as USB keys exposes the system to potential compromise.

identifiers:  CCE-80147-2

references:  AC-19(a), AC-19(d), AC-19(e), CM-7, MP-2, 87, 1.1.12

Add nosuid Option to Removable Media Partitions   [ref]rule

The nosuid mount option prevents set-user-identifier (SUID) and set-group-identifier (SGID) permissions from taking effect. These permissions allow users to execute binaries with the same permissions as the owner and group of the file respectively. Users should not be allowed to introduce SUID and SGID files into the system via partitions mounted from removeable media. Add the nosuid option to the fourth column of /etc/fstab for the line which controls mounting of any removable media partitions.

Rationale:

The presence of SUID and SGID executables should be tightly controlled. Allowing users to introduce SUID or SGID binaries from partitions mounted off of removable media would allow them to introduce their own highly-privileged programs.

identifiers:  CCE-80148-0

references:  AC-6, AC-19(a), AC-19(d), AC-19(e), CM-7, MP-2, 1.1.13, 366, SRG-OS-000480-GPOS-00227, RHEL-07-021010

Restrict Dynamic Mounting and Unmounting of Filesystems   [ref]group

Linux includes a number of facilities for the automated addition and removal of filesystems on a running system. These facilities may be necessary in many environments, but this capability also carries some risk -- whether direct risk from allowing users to introduce arbitrary filesystems, or risk that software flaws in the automated mount facility itself could allow an attacker to compromise the system.

This command can be used to list the types of filesystems that are available to the currently executing kernel:

$ find /lib/modules/`uname -r`/kernel/fs -type f -name '*.ko'
If these filesystems are not required then they can be explicitly disabled in a configuratio file in /etc/modprobe.d.

contains 5 rules

Disable Modprobe Loading of USB Storage Driver   [ref]rule

To prevent USB storage devices from being used, configure the kernel module loading system to prevent automatic loading of the USB storage driver. To configure the system to prevent the usb-storage kernel module from being loaded, add the following line to a file in the directory /etc/modprobe.d:

install usb-storage /bin/true
This will prevent the modprobe program from loading the usb-storage module, but will not prevent an administrator (or another program) from using the insmod program to load the module manually.

Rationale:

USB storage devices such as thumb drives can be used to introduce malicious software.

Remediation Shell script:   (show)

Complexity:low
Disruption:medium
Reboot:true
Strategy:disable
if grep --silent "^install usb-storage" /etc/modprobe.d/usb-storage.conf ; then
        sed -i 's/^install usb-storage.*/install usb-storage /bin/true/g' /etc/modprobe.d/usb-storage.conf
else
        echo -e "\n# Disable per security requirements" >> /etc/modprobe.d/usb-storage.conf
        echo "install usb-storage /bin/true" >> /etc/modprobe.d/usb-storage.conf
fi
Remediation Ansible snippet:   (show)

Complexity:low
Disruption:medium
Reboot:true
Strategy:disable
- name: Ensure kernel module 'usb-storage' is disabled
  lineinfile:
    create=yes
    dest="/etc/modprobe.d/{{item}}.conf"
    regexp="{{item}}"
    line="install {{item}} /bin/true"
  with_items:
    - usb-storage

Disable Kernel Support for USB via Bootloader Configuration   [ref]rule

All USB support can be disabled by adding the nousb argument to the kernel's boot loader configuration. To do so, append "nousb" to the kernel line in /etc/default/grub as shown:

kernel /vmlinuz-VERSION ro vga=ext root=/dev/VolGroup00/LogVol00 rhgb quiet nousb
WARNING: Disabling all kernel support for USB will cause problems for systems with USB-based keyboards, mice, or printers. This configuration is infeasible for systems which require USB devices, which is common.

Rationale:

Disabling the USB subsystem within the Linux kernel at system boot will protect against potentially malicious USB devices, although it is only practical in specialized systems.

identifiers:  CCE-26548-8

references:  AC-19(a), AC-19(d), AC-19(e), 1250

Remediation Shell script:   (show)

Complexity:high
Disruption:medium
Strategy:restrict

# Correct the form of default kernel command line in /etc/default/grub
if ! grep -q ^GRUB_CMDLINE_LINUX=\".*nousb.*\" /etc/default/grub;
then
  # Edit configuration setting
  # Append 'nousb' argument to /etc/default/grub (if not present yet)
  sed -i "s/\(GRUB_CMDLINE_LINUX=\)\"\(.*\)\"/\1\"\2 nousb\"/" /etc/default/grub
  # Edit runtime setting
  # Correct the form of kernel command line for each installed kernel in the bootloader
  /sbin/grubby --update-kernel=ALL --args="nousb"
fi

Disable Booting from USB Devices in Boot Firmware   [ref]rule

Configure the system boot firmware (historically called BIOS on PC systems) to disallow booting from USB drives.

Rationale:

Booting a system from a USB device would allow an attacker to circumvent any security measures provided by the operating system. Attackers could mount partitions and modify the configuration of the OS.

identifiers:  CCE-26960-5

references:  AC-19(a), AC-19(d), AC-19(e), 1250

Assign Password to Prevent Changes to Boot Firmware Configuration   [ref]rule

Assign a password to the system boot firmware (historically called BIOS on PC systems) to require a password for any configuration changes.

Rationale:

Assigning a password to the system boot firmware prevents anyone with physical access from configuring the system to boot from local media and circumvent the operating system's access controls. For systems in physically secure locations, such as a data center or Sensitive Compartmented Information Facility (SCIF), this risk must be weighed against the risk of administrative personnel being unable to conduct recovery operations in a timely fashion.

identifiers:  CCE-27194-0

Disable the Automounter   [ref]rule

The autofs daemon mounts and unmounts filesystems, such as user home directories shared via NFS, on demand. In addition, autofs can be used to handle removable media, and the default configuration provides the cdrom device as /misc/cd. However, this method of providing access to removable media is not common, so autofs can almost always be disabled if NFS is not in use. Even if NFS is required, it may be possible to configure filesystem mounts statically by editing /etc/fstab rather than relying on the automounter.

The autofs service can be disabled with the following command:

$ sudo systemctl disable autofs.service

Rationale:

Disabling the automounter permits the administrator to statically control filesystem mounting through /etc/fstab.

Additionally, automatically mounting filesystems permits easy introduction of unknown devices, thereby facilitating malicious activity.

Remediation Shell script:   (show)

Complexity:low
Disruption:low
Strategy:disable

function service_command {

# Load function arguments into local variables
local service_state=$1
local service=$2
local xinetd=$(echo $3 | cut -d'=' -f2)

# Check sanity of the input
if [ $# -lt "2" ]
then
  echo "Usage: service_command 'enable/disable' 'service_name.service'"
  echo
  echo "To enable or disable xinetd services add \'xinetd=service_name\'"
  echo "as the last argument"
  echo "Aborting."
  exit 1
fi

# If systemctl is installed, use systemctl command; otherwise, use the service/chkconfig commands
if [ -f "/usr/bin/systemctl" ] ; then
  service_util="/usr/bin/systemctl"
else
  service_util="/sbin/service"
  chkconfig_util="/sbin/chkconfig"
fi

# If disable is not specified in arg1, set variables to enable services.
# Otherwise, variables are to be set to disable services.
if [ "$service_state" != 'disable' ] ; then
  service_state="enable"
  service_operation="start"
  chkconfig_state="on"
else
  service_state="disable"
  service_operation="stop"
  chkconfig_state="off"
fi

# If chkconfig_util is not empty, use chkconfig/service commands.
if ! [ "x$chkconfig_util" = x ] ; then
  $service_util $service $service_operation
  $chkconfig_util --level 0123456 $service $chkconfig_state
else
  $service_util $service_operation $service
  $service_util $service_state $service
fi

# Test if local variable xinetd is empty using non-bashism.
# If empty, then xinetd is not being used.
if ! [ "x$xinetd" = x ] ; then
  grep -qi disable /etc/xinetd.d/$xinetd && \

  if ! [ "$service_operation" != 'disable' ] ; then
    sed -i "s/disable.*/disable         = no/gI" /etc/xinetd.d/$xinetd
  else
    sed -i "s/disable.*/disable         = yes/gI" /etc/xinetd.d/$xinetd
  fi
fi

}

service_command disable autofs
Remediation Ansible snippet:   (show)

Complexity:low
Disruption:low
Strategy:disable
- name: Disable service autofs
  service:
    name="{{item}}"
    enabled="no"
    state="stopped"
  with_items:
    - autofs

Verify Permissions on Important Files and Directories   [ref]group

Permissions for many files on a system must be set restrictively to ensure sensitive information is properly protected. This section discusses important permission restrictions which can be verified to ensure that no harmful discrepancies have arisen.

contains 3 rules

Ensure All Files Are Owned by a User   [ref]rule

If any files are not owned by a user, then the cause of their lack of ownership should be investigated. Following this, the files should be deleted or assigned to an appropriate user.

Rationale:

Unowned files do not directly imply a security problem, but they are generally a sign that something is amiss. They may be caused by an intruder, by incorrect software installation or draft software removal, or by failure to remove all files belonging to a deleted account. The files should be repaired so they will not cause problems when accounts are created in the future, and the cause should be discovered and addressed.

identifiers:  CCE-80134-0

references:  AC-3(4), AC-6, CM-6(b), 002165, SRG-OS-000480-GPOS-00227, RHEL-07-020320

Ensure All Files Are Owned by a Group   [ref]rule

If any files are not owned by a group, then the cause of their lack of group-ownership should be investigated. Following this, the files should be deleted or assigned to an appropriate group.

Rationale:

Unowned files do not directly imply a security problem, but they are generally a sign that something is amiss. They may be caused by an intruder, by incorrect software installation or draft software removal, or by failure to remove all files belonging to a deleted account. The files should be repaired so they will not cause problems when accounts are created in the future, and the cause should be discovered and addressed.

identifiers:  CCE-80135-7

references:  AC-3(4), AC-6, IA-2, 02165, SRG-OS-000480-GPOS-00227, RHEL-07-020330

Ensure All World-Writable Directories Are Owned by a System Account   [ref]rule

All directories in local partitions which are world-writable should be owned by root or another system account. If any world-writable directories are not owned by a system account, this should be investigated. Following this, the files should be deleted or assigned to an appropriate group.

Rationale:

Allowing a user account to own a world-writable directory is undesirable because it allows the owner of that directory to remove or replace any files that may be placed in the directory by other users.

identifiers:  CCE-80136-5

references:  AC-6, 366, SRG-OS-000480-GPOS-00227, RHEL-07-021030

Restrict Programs from Dangerous Execution Patterns   [ref]group

The recommendations in this section are designed to ensure that the system's features to protect against potentially dangerous program execution are activated. These protections are applied at the system initialization or kernel level, and defend against certain types of badly-configured or compromised programs.

contains 6 rules

Disable Core Dumps   [ref]group

A core dump file is the memory image of an executable program when it was terminated by the operating system due to errant behavior. In most cases, only software developers legitimately need to access these files. The core dump files may also contain sensitive information, or unnecessarily occupy large amounts of disk space.

Once a hard limit is set in /etc/security/limits.conf, a user cannot increase that limit within his or her own session. If access to core dumps is required, consider restricting them to only certain users or groups. See the limits.conf man page for more information.

The core dumps of setuid programs are further protected. The sysctl variable fs.suid_dumpable controls whether the kernel allows core dumps from these programs at all. The default value of 0 is recommended.

contains 1 rule

Disable Core Dumps for SUID programs   [ref]rule

To set the runtime status of the fs.suid_dumpable kernel parameter, run the following command:

$ sudo sysctl -w fs.suid_dumpable=0
If this is not the system's default value, add the following line to /etc/sysctl.conf:
fs.suid_dumpable = 0

Rationale:

The core dump of a setuid program is more likely to contain sensitive data, as the program itself runs with greater privileges than the user who initiated execution of the program. Disabling the ability for any setuid program to write a core file decreases the risk of unauthorized access of such data.

identifiers:  CCE-26900-1

references:  SI-11, 1.6.1

Remediation Shell script:   (show)

Complexity:low
Disruption:medium
Reboot:true
Strategy:disable


#
# Set runtime for fs.suid_dumpable
#
/sbin/sysctl -q -n -w fs.suid_dumpable=0

#
# If fs.suid_dumpable present in /etc/sysctl.conf, change value to "0"
#	else, add "fs.suid_dumpable = 0" to /etc/sysctl.conf
#

function replace_or_append {
  local config_file=$1
  local key=$2
  local value=$3
  local cce=$4
  local format=$5

  # Check sanity of the input
  if [ $# -lt "3" ]
  then
        echo "Usage: replace_or_append 'config_file_location' 'key_to_search' 'new_value'"
        echo
        echo "If symlinks need to be taken into account, add yes/no to the last argument"
        echo "to allow to 'follow_symlinks'."
        echo "Aborting."
        exit 1
  fi

  # Test if the config_file is a symbolic link. If so, use --follow-symlinks with sed.
  # Otherwise, regular sed command will do.
  if test -L $config_file; then
    sed_command="sed -i --follow-symlinks"
  else
    sed_command="sed -i"
  fi

  # Test that the cce arg is not empty or does not equal $CCENUM.
  # If $CCENUM exists, it means that there is no CCE assigned.
  if ! [ "x$cce" = x ] && [ "$cce" != '$CCENUM' ]; then
    cce="CCE-${cce}"
  else
    cce="CCE"
  fi

  # Strip any search characters in the key arg so that the key can be replaced without
  # adding any search characters to the config file.
  stripped_key=$(sed "s/[\^=\$,;+]*//g" <<< $key)

  # If there is no print format specified in the last arg, use the default format.
  if ! [ "x$format" = x ] ; then
    printf -v formatted_output "$format" $stripped_key $value
  else
    formatted_output="$stripped_key = $value"
  fi

  # If the key exists, change it. Otherwise, add it to the config_file.
  if `grep -qi $key $config_file` ; then
    $sed_command "s/$key.*/$formatted_output/g" $config_file
  else
    # \n is precaution for case where file ends without trailing newline
    echo -e "\n# Per $cce: Set $formatted_output in $config_file" >> $config_file
    echo -e "$formatted_output" >> $config_file
  fi

}

replace_or_append '/etc/sysctl.conf' '^fs.suid_dumpable' '0' 'CCE-26900-1'

Enable ExecShield   [ref]group

ExecShield describes kernel features that provide protection against exploitation of memory corruption errors such as buffer overflows. These features include random placement of the stack and other memory regions, prevention of execution in memory that should only hold data, and special handling of text buffers. These protections are enabled by default on 32-bit systems and controlled through sysctl variables kernel.exec-shield and kernel.randomize_va_space. On the latest 64-bit systems, kernel.exec-shield cannot be enabled or disabled with sysctl.

contains 2 rules

Enable ExecShield   [ref]rule

By default on Red Hat Enterprise Linux 7 64-bit systems, ExecShield is enabled and can only be disabled if the hardware does not support ExecShield or is disabled in /etc/default/grub. For Red Hat Enterprise Linux 7 32-bit systems, sysctl can be used to enable ExecShield.

Rationale:

ExecShield uses the segmentation feature on all x86 systems to prevent execution in memory higher than a certain address. It writes an address as a limit in the code segment descriptor, to control where code can be executed, on a per-process basis. When the kernel places a process's memory regions such as the stack and heap higher than this address, the hardware prevents execution in that address range. This is enabled by default on the latest Red Hat and Fedora systems if supported by the hardware.

identifiers:  CCE-27211-2

references:  SC-39, 2530, 3.1.7

Remediation Shell script:   (show)

Complexity:low
Disruption:low
Strategy:disable


if [ $(getconf LONG_BIT) = "32" ] ; then
  #
  # Set runtime for kernel.exec-shield
  #
  sysctl -q -n -w kernel.exec-shield=1

  #
  # If kernel.exec-shield present in /etc/sysctl.conf, change value to "1"
  #	else, add "kernel.exec-shield = 1" to /etc/sysctl.conf
  #

function replace_or_append {
  local config_file=$1
  local key=$2
  local value=$3
  local cce=$4
  local format=$5

  # Check sanity of the input
  if [ $# -lt "3" ]
  then
        echo "Usage: replace_or_append 'config_file_location' 'key_to_search' 'new_value'"
        echo
        echo "If symlinks need to be taken into account, add yes/no to the last argument"
        echo "to allow to 'follow_symlinks'."
        echo "Aborting."
        exit 1
  fi

  # Test if the config_file is a symbolic link. If so, use --follow-symlinks with sed.
  # Otherwise, regular sed command will do.
  if test -L $config_file; then
    sed_command="sed -i --follow-symlinks"
  else
    sed_command="sed -i"
  fi

  # Test that the cce arg is not empty or does not equal $CCENUM.
  # If $CCENUM exists, it means that there is no CCE assigned.
  if ! [ "x$cce" = x ] && [ "$cce" != '$CCENUM' ]; then
    cce="CCE-${cce}"
  else
    cce="CCE"
  fi

  # Strip any search characters in the key arg so that the key can be replaced without
  # adding any search characters to the config file.
  stripped_key=$(sed "s/[\^=\$,;+]*//g" <<< $key)

  # If there is no print format specified in the last arg, use the default format.
  if ! [ "x$format" = x ] ; then
    printf -v formatted_output "$format" $stripped_key $value
  else
    formatted_output="$stripped_key = $value"
  fi

  # If the key exists, change it. Otherwise, add it to the config_file.
  if `grep -qi $key $config_file` ; then
    $sed_command "s/$key.*/$formatted_output/g" $config_file
  else
    # \n is precaution for case where file ends without trailing newline
    echo -e "\n# Per $cce: Set $formatted_output in $config_file" >> $config_file
    echo -e "$formatted_output" >> $config_file
  fi

}

  replace_or_append '/etc/sysctl.conf' '^kernel.exec-shield' '1' 'CCE-27211-2'
fi

if [ $(getconf LONG_BIT) = "64" ] ; then
  if grep --silent noexec /boot/grub2/grub*.cfg ; then 
        sed -i "s/noexec.*//g" /etc/default/grub
        sed -i "s/noexec.*//g" /etc/grub.d/*
        GRUBCFG=`ls | grep '.cfg$'`
        grub2-mkconfig -o /boot/grub2/$GRUBCFG
  fi
fi

Enable Randomized Layout of Virtual Address Space   [ref]rule

To set the runtime status of the kernel.randomize_va_space kernel parameter, run the following command:

$ sudo sysctl -w kernel.randomize_va_space=2
If this is not the system's default value, add the following line to /etc/sysctl.conf:
kernel.randomize_va_space = 2

Rationale:

Address space layout randomization (ASLR) makes it more difficult for an attacker to predict the location of attack code they have introduced into a process's address space during an attempt at exploitation. Additionally, ASLR makes it more difficult for an attacker to know the location of existing code in order to re-purpose it using return oriented programming (ROP) techniques.

identifiers:  CCE-27127-0

references:  SC-30(2), 1.6.1, 3.1.7

Remediation Shell script:   (show)

Complexity:low
Disruption:medium
Reboot:true
Strategy:disable

function replace_or_append {
  local config_file=$1
  local key=$2
  local value=$3
  local cce=$4
  local format=$5

  # Check sanity of the input
  if [ $# -lt "3" ]
  then
        echo "Usage: replace_or_append 'config_file_location' 'key_to_search' 'new_value'"
        echo
        echo "If symlinks need to be taken into account, add yes/no to the last argument"
        echo "to allow to 'follow_symlinks'."
        echo "Aborting."
        exit 1
  fi

  # Test if the config_file is a symbolic link. If so, use --follow-symlinks with sed.
  # Otherwise, regular sed command will do.
  if test -L $config_file; then
    sed_command="sed -i --follow-symlinks"
  else
    sed_command="sed -i"
  fi

  # Test that the cce arg is not empty or does not equal $CCENUM.
  # If $CCENUM exists, it means that there is no CCE assigned.
  if ! [ "x$cce" = x ] && [ "$cce" != '$CCENUM' ]; then
    cce="CCE-${cce}"
  else
    cce="CCE"
  fi

  # Strip any search characters in the key arg so that the key can be replaced without
  # adding any search characters to the config file.
  stripped_key=$(sed "s/[\^=\$,;+]*//g" <<< $key)

  # If there is no print format specified in the last arg, use the default format.
  if ! [ "x$format" = x ] ; then
    printf -v formatted_output "$format" $stripped_key $value
  else
    formatted_output="$stripped_key = $value"
  fi

  # If the key exists, change it. Otherwise, add it to the config_file.
  if `grep -qi $key $config_file` ; then
    $sed_command "s/$key.*/$formatted_output/g" $config_file
  else
    # \n is precaution for case where file ends without trailing newline
    echo -e "\n# Per $cce: Set $formatted_output in $config_file" >> $config_file
    echo -e "$formatted_output" >> $config_file
  fi

}

replace_or_append '/etc/sysctl.conf' '^kernel.randomize_va_space' '2' 'CCE-27127-0'

Enable Execute Disable (XD) or No Execute (NX) Support on x86 Systems   [ref]group

Recent processors in the x86 family support the ability to prevent code execution on a per memory page basis. Generically and on AMD processors, this ability is called No Execute (NX), while on Intel processors it is called Execute Disable (XD). This ability can help prevent exploitation of buffer overflow vulnerabilities and should be activated whenever possible. Extra steps must be taken to ensure that this protection is enabled, particularly on 32-bit x86 systems. Other processors, such as Itanium and POWER, have included such support since inception and the standard kernel for those platforms supports the feature. This is enabled by default on the latest Red Hat and Fedora systems if supported by the hardware.

contains 2 rules

Install PAE Kernel on Supported 32-bit x86 Systems   [ref]rule

Systems that are using the 64-bit x86 kernel package do not need to install the kernel-PAE package because the 64-bit x86 kernel already includes this support. However, if the system is 32-bit and also supports the PAE and NX features as determined in the previous section, the kernel-PAE package should be installed to enable XD or NX support:

$ sudo yum install kernel-PAE
The installation process should also have configured the bootloader to load the new kernel at boot. Verify this at reboot and modify /etc/default/grub if necessary.

warning  The kernel-PAE package should not be installed on older systems that do not support the XD or NX bit, as this may prevent them from booting.
Rationale:

On 32-bit systems that support the XD or NX bit, the vendor-supplied PAE kernel is required to enable either Execute Disable (XD) or No Execute (NX) support.

identifiers:  CCE-27116-3

references:  CM-6(b), 3.1.7

Enable NX or XD Support in the BIOS   [ref]rule

Reboot the system and enter the BIOS or Setup configuration menu. Navigate the BIOS configuration menu and make sure that the option is enabled. The setting may be located under a Security section. Look for Execute Disable (XD) on Intel-based systems and No Execute (NX) on AMD-based systems.

Rationale:

Computers with the ability to prevent this type of code execution frequently put an option in the BIOS that will allow users to turn the feature on or off at will.

identifiers:  CCE-27099-1

references:  CM-6(b), 3.1.7

Restrict Access to Kernel Message Buffer   [ref]rule

To set the runtime status of the kernel.dmesg_restrict kernel parameter, run the following command:

$ sudo sysctl -w kernel.dmesg_restrict=1
If this is not the system's default value, add the following line to /etc/sysctl.conf:
kernel.dmesg_restrict = 1

Rationale:

Unprivileged access to the kernel syslog can expose sensitive kernel address information.

identifiers:  CCE-27050-4

references:  SI-11, 1314, 3.1.5

Remediation Shell script:   (show)

Complexity:low
Disruption:medium
Reboot:true
Strategy:disable


#
# Set runtime for kernel.dmesg_restrict
#
/sbin/sysctl -q -n -w kernel.dmesg_restrict=1

#
# If kernel.dmesg_restrict present in /etc/sysctl.conf, change value to "1"
#	else, add "kernel.dmesg_restrict = 1" to /etc/sysctl.conf
#

function replace_or_append {
  local config_file=$1
  local key=$2
  local value=$3
  local cce=$4
  local format=$5

  # Check sanity of the input
  if [ $# -lt "3" ]
  then
        echo "Usage: replace_or_append 'config_file_location' 'key_to_search' 'new_value'"
        echo
        echo "If symlinks need to be taken into account, add yes/no to the last argument"
        echo "to allow to 'follow_symlinks'."
        echo "Aborting."
        exit 1
  fi

  # Test if the config_file is a symbolic link. If so, use --follow-symlinks with sed.
  # Otherwise, regular sed command will do.
  if test -L $config_file; then
    sed_command="sed -i --follow-symlinks"
  else
    sed_command="sed -i"
  fi

  # Test that the cce arg is not empty or does not equal $CCENUM.
  # If $CCENUM exists, it means that there is no CCE assigned.
  if ! [ "x$cce" = x ] && [ "$cce" != '$CCENUM' ]; then
    cce="CCE-${cce}"
  else
    cce="CCE"
  fi

  # Strip any search characters in the key arg so that the key can be replaced without
  # adding any search characters to the config file.
  stripped_key=$(sed "s/[\^=\$,;+]*//g" <<< $key)

  # If there is no print format specified in the last arg, use the default format.
  if ! [ "x$format" = x ] ; then
    printf -v formatted_output "$format" $stripped_key $value
  else
    formatted_output="$stripped_key = $value"
  fi

  # If the key exists, change it. Otherwise, add it to the config_file.
  if `grep -qi $key $config_file` ; then
    $sed_command "s/$key.*/$formatted_output/g" $config_file
  else
    # \n is precaution for case where file ends without trailing newline
    echo -e "\n# Per $cce: Set $formatted_output in $config_file" >> $config_file
    echo -e "$formatted_output" >> $config_file
  fi

}

replace_or_append '/etc/sysctl.conf' '^kernel.dmesg_restrict' '1' 'CCE-27050-4'

SELinux   [ref]group

SELinux is a feature of the Linux kernel which can be used to guard against misconfigured or compromised programs. SELinux enforces the idea that programs should be limited in what files they can access and what actions they can take.

The default SELinux policy, as configured on Red Hat Enterprise Linux 7, has been sufficiently developed and debugged that it should be usable on almost any Red Hat system with minimal configuration and a small amount of system administrator training. This policy prevents system services - including most of the common network-visible services such as mail servers, FTP servers, and DNS servers - from accessing files which those services have no valid reason to access. This action alone prevents a huge amount of possible damage from network attacks against services, from trojaned software, and so forth.

This guide recommends that SELinux be enabled using the default (targeted) policy on every Red Hat system, unless that system has unusual requirements which make a stronger policy appropriate.

For more information on SELinux, see https://access.redhat.com/documentation/en-US/Red_Hat_Enterprise_Linux/7/html/SELinux_Users_and_Administrators_Guide

contains 5 rules

Ensure SELinux Not Disabled in /etc/default/grub   [ref]rule

SELinux can be disabled at boot time by an argument in /etc/default/grub. Remove any instances of selinux=0 from the kernel arguments in that file to prevent SELinux from being disabled at boot.

Rationale:

Disabling a major host protection feature, such as SELinux, at boot time prevents it from confining system services at boot time. Further, it increases the chances that it will remain off during system operation.

identifiers:  CCE-26961-3

references:  AC-3, AC-3(3), AC-3(4), AC-4, AC-6, AU-9, SI-6(a), 22, 32, 1.4.1, 3.1.2, 3.7.2

Remediation Shell script:   (show)

Complexity:low
Disruption:low
Strategy:disable
sed -i --follow-symlinks "s/selinux=0//gI" /etc/default/grub /etc/grub2.cfg /etc/grub.d/*
sed -i --follow-symlinks "s/enforcing=0//gI" /etc/default/grub /etc/grub2.cfg /etc/grub.d/*

Ensure SELinux State is Enforcing   [ref]rule

The SELinux state should be set to enforcing at system boot time. In the file /etc/selinux/config, add or correct the following line to configure the system to boot into enforcing mode:

SELINUX=enforcing

Rationale:

Setting the SELinux state to enforcing ensures SELinux is able to confine potentially compromised processes to the security policy, which is designed to prevent them from causing damage to the system or further elevating their privileges.

identifiers:  CCE-27334-2

references:  AC-3, AC-3(3), AC-3(4), AC-4, AC-6, AU-9, SI-6(a), 2165, 2696, 1.4.2, SRG-OS-000445-GPOS-00199, RHEL-07-020210, 3.1.2, 3.7.2

Remediation Shell script:   (show)

Complexity:low
Disruption:low
Strategy:disable

var_selinux_state="enforcing"

function replace_or_append {
  local config_file=$1
  local key=$2
  local value=$3
  local cce=$4
  local format=$5

  # Check sanity of the input
  if [ $# -lt "3" ]
  then
        echo "Usage: replace_or_append 'config_file_location' 'key_to_search' 'new_value'"
        echo
        echo "If symlinks need to be taken into account, add yes/no to the last argument"
        echo "to allow to 'follow_symlinks'."
        echo "Aborting."
        exit 1
  fi

  # Test if the config_file is a symbolic link. If so, use --follow-symlinks with sed.
  # Otherwise, regular sed command will do.
  if test -L $config_file; then
    sed_command="sed -i --follow-symlinks"
  else
    sed_command="sed -i"
  fi

  # Test that the cce arg is not empty or does not equal $CCENUM.
  # If $CCENUM exists, it means that there is no CCE assigned.
  if ! [ "x$cce" = x ] && [ "$cce" != '$CCENUM' ]; then
    cce="CCE-${cce}"
  else
    cce="CCE"
  fi

  # Strip any search characters in the key arg so that the key can be replaced without
  # adding any search characters to the config file.
  stripped_key=$(sed "s/[\^=\$,;+]*//g" <<< $key)

  # If there is no print format specified in the last arg, use the default format.
  if ! [ "x$format" = x ] ; then
    printf -v formatted_output "$format" $stripped_key $value
  else
    formatted_output="$stripped_key = $value"
  fi

  # If the key exists, change it. Otherwise, add it to the config_file.
  if `grep -qi $key $config_file` ; then
    $sed_command "s/$key.*/$formatted_output/g" $config_file
  else
    # \n is precaution for case where file ends without trailing newline
    echo -e "\n# Per $cce: Set $formatted_output in $config_file" >> $config_file
    echo -e "$formatted_output" >> $config_file
  fi

}

replace_or_append '/etc/sysconfig/selinux' '^SELINUX=' $var_selinux_state 'CCE-27334-2' '%s=%s'

Configure SELinux Policy   [ref]rule

The SELinux targeted policy is appropriate for general-purpose desktops and servers, as well as systems in many other roles. To configure the system to use this policy, add or correct the following line in /etc/selinux/config:

SELINUXTYPE=targeted
Other policies, such as mls, provide additional security labeling and greater confinement but are not compatible with many general-purpose use cases.

Rationale:

Setting the SELinux policy to targeted or a more specialized policy ensures the system will confine processes that are likely to be targeted for exploitation, such as network or system services.

Note: During the development or debugging of SELinux modules, it is common to temporarily place non-production systems in permissive mode. In such temporary cases, SELinux policies should be developed, and once work is completed, the system should be reconfigured to targeted.

identifiers:  CCE-27279-9

references:  AC-3, AC-3(3), AC-3(4), AC-4, AC-6, AU-9, SI-6(a), 2696, 1.4.3, SRG-OS-000445-GPOS-00199, RHEL-07-020220, 3.1.2, 3.7.2

Remediation Shell script:   (show)

Complexity:low
Disruption:low
Strategy:disable

var_selinux_policy_name="targeted"

function replace_or_append {
  local config_file=$1
  local key=$2
  local value=$3
  local cce=$4
  local format=$5

  # Check sanity of the input
  if [ $# -lt "3" ]
  then
        echo "Usage: replace_or_append 'config_file_location' 'key_to_search' 'new_value'"
        echo
        echo "If symlinks need to be taken into account, add yes/no to the last argument"
        echo "to allow to 'follow_symlinks'."
        echo "Aborting."
        exit 1
  fi

  # Test if the config_file is a symbolic link. If so, use --follow-symlinks with sed.
  # Otherwise, regular sed command will do.
  if test -L $config_file; then
    sed_command="sed -i --follow-symlinks"
  else
    sed_command="sed -i"
  fi

  # Test that the cce arg is not empty or does not equal $CCENUM.
  # If $CCENUM exists, it means that there is no CCE assigned.
  if ! [ "x$cce" = x ] && [ "$cce" != '$CCENUM' ]; then
    cce="CCE-${cce}"
  else
    cce="CCE"
  fi

  # Strip any search characters in the key arg so that the key can be replaced without
  # adding any search characters to the config file.
  stripped_key=$(sed "s/[\^=\$,;+]*//g" <<< $key)

  # If there is no print format specified in the last arg, use the default format.
  if ! [ "x$format" = x ] ; then
    printf -v formatted_output "$format" $stripped_key $value
  else
    formatted_output="$stripped_key = $value"
  fi

  # If the key exists, change it. Otherwise, add it to the config_file.
  if `grep -qi $key $config_file` ; then
    $sed_command "s/$key.*/$formatted_output/g" $config_file
  else
    # \n is precaution for case where file ends without trailing newline
    echo -e "\n# Per $cce: Set $formatted_output in $config_file" >> $config_file
    echo -e "$formatted_output" >> $config_file
  fi

}

replace_or_append '/etc/sysconfig/selinux' '^SELINUXTYPE=' $var_selinux_policy_name 'CCE-27279-9' '%s=%s'

Ensure No Daemons are Unconfined by SELinux   [ref]rule

Daemons for which the SELinux policy does not contain rules will inherit the context of the parent process. Because daemons are launched during startup and descend from the init process, they inherit the initrc_t context.

To check for unconfined daemons, run the following command:

$ sudo ps -eZ | egrep "initrc" | egrep -vw "tr|ps|egrep|bash|awk" | tr ':' ' ' | awk '{ print $NF }'
It should produce no output in a well-configured system.

Rationale:

Daemons which run with the initrc_t context may cause AVC denials, or allow privileges that the daemon does not require.

identifiers:  CCE-27288-0

references:  AC-6, AU-9, CM-7, 1.4.6, 3.1.2, 3.1.5, 3.7.2

Ensure No Device Files are Unlabeled by SELinux   [ref]rule

Device files, which are used for communication with important system resources, should be labeled with proper SELinux types. If any device files do not carry the SELinux type device_t, report the bug so that policy can be corrected. Supply information about what the device is and what programs use it.

To check for unlabeled device files, run the following command:

$ sudo find /dev -context *:device_t:* \( -type c -o -type b \) -printf "%p %Z\n"
It should produce no output in a well-configured system.

Rationale:

If a device file carries the SELinux type device_t, then SELinux cannot properly restrict access to the device file.

identifiers:  CCE-27326-8

references:  AC-6, AU-9, CM-3(f), CM-7, 22, 32, 368, 318, 1812, 1813, 1814, RHEL-07-020900, SRG-OS-000480-GPOS-00227, 3.1.2, 3.1.5, 3.7.2

Account and Access Control   [ref]group

In traditional Unix security, if an attacker gains shell access to a certain login account, they can perform any action or access any file to which that account has access. Therefore, making it more difficult for unauthorized people to gain shell access to accounts, particularly to privileged accounts, is a necessary part of securing a system. This section introduces mechanisms for restricting access to accounts under Red Hat Enterprise Linux 7.

contains 45 rules

Protect Accounts by Restricting Password-Based Login   [ref]group

Conventionally, Unix shell accounts are accessed by providing a username and password to a login program, which tests these values for correctness using the /etc/passwd and /etc/shadow files. Password-based login is vulnerable to guessing of weak passwords, and to sniffing and man-in-the-middle attacks against passwords entered over a network or at an insecure console. Therefore, mechanisms for accessing accounts by entering usernames and passwords should be restricted to those which are operationally necessary.

contains 11 rules

Restrict Root Logins   [ref]group

Direct root logins should be allowed only for emergency use. In normal situations, the administrator should access the system via a unique unprivileged account, and then use su or sudo to execute privileged commands. Discouraging administrators from accessing the root account directly ensures an audit trail in organizations with multiple administrators. Locking down the channels through which root can connect directly also reduces opportunities for password-guessing against the root account. The login program uses the file /etc/securetty to determine which interfaces should allow root logins. The virtual devices /dev/console and /dev/tty* represent the system consoles (accessible via the Ctrl-Alt-F1 through Ctrl-Alt-F6 keyboard sequences on a default installation). The default securetty file also contains /dev/vc/*. These are likely to be deprecated in most environments, but may be retained for compatibility. Root should also be prohibited from connecting via network protocols. Other sections of this document include guidance describing how to prevent root from logging in via SSH.

contains 4 rules

Direct root Logins Not Allowed   [ref]rule

To further limit access to the root account, administrators can disable root logins at the console by editing the /etc/securetty file. This file lists all devices the root user is allowed to login to. If the file does not exist at all, the root user can login through any communication device on the system, whether via the console or via a raw network interface. This is dangerous as user can login to the system as root via Telnet, which sends the password in plain text over the network. By default, Red Hat Enteprise Linux's /etc/securetty file only allows the root user to login at the console physically attached to the system. To prevent root from logging in, remove the contents of this file. To prevent direct root logins, remove the contents of this file by typing the following command:

$ sudo echo > /etc/securetty

Rationale:

Disabling direct root logins ensures proper accountability and multifactor authentication to privileged accounts. Users will first login, then escalate to privileged (root) access via su / sudo. This is required for FISMA Low and FISMA Moderate systems.

identifiers:  CCE-27294-8

references:  IA-2(1), 6.4, 3.1.1, 3.1.6

Remediation Shell script:   (show)

Complexity:high
Disruption:medium
Strategy:restrict
echo > /etc/securetty

Restrict Serial Port Root Logins   [ref]rule

To restrict root logins on serial ports, ensure lines of this form do not appear in /etc/securetty:

ttyS0
ttyS1

Rationale:

Preventing direct root login to serial port interfaces helps ensure accountability for actions taken on the systems using the root account.

identifiers:  CCE-27268-2

references:  AC-6(2), 770, 3.1.1, 3.1.5

Remediation Shell script:   (show)

Complexity:low
Disruption:low
Strategy:disable
sed -i '/ttyS/d' /etc/securetty

Verify Only Root Has UID 0   [ref]rule

If any account other than root has a UID of 0, this misconfiguration should be investigated and the accounts other than root should be removed or have their UID changed.
If the account is associated with system commands or applications the UID should be changed to one greater than "0" but less than "1000." Otherwise assign a UID greater than "1000" that has not already been assigned.

Rationale:

An account has root authority if it has a UID of 0. Multiple accounts with a UID of 0 afford more opportunity for potential intruders to guess a password for a privileged account. Proper configuration of sudo is recommended to afford multiple system administrators access to root privileges in an accountable manner.

identifiers:  CCE-27175-9

references:  AC-6, IA-2(1), IA-4, 366, SRG-OS-000480-GPOS-00227, RHEL-07-020310, 3.1.1, 3.1.5

Remediation Shell script:   (show)

Complexity:low
Disruption:low
Strategy:disable
awk -F: '$3 == 0 && $1 != "root" { print $1 }' /etc/passwd | xargs passwd -l

Verify Proper Storage and Existence of Password Hashes   [ref]group

By default, password hashes for local accounts are stored in the second field (colon-separated) in /etc/shadow. This file should be readable only by processes running with root credentials, preventing users from casually accessing others' password hashes and attempting to crack them. However, it remains possible to misconfigure the system and store password hashes in world-readable files such as /etc/passwd, or to even store passwords themselves in plaintext on the system. Using system-provided tools for password change/creation should allow administrators to avoid such misconfiguration.

contains 3 rules

Prevent Log In to Accounts With Empty Password   [ref]rule

If an account is configured for password authentication but does not have an assigned password, it may be possible to log into the account without authentication. Remove any instances of the nullok option in /etc/pam.d/system-auth to prevent logins with empty passwords.

Rationale:

If an account has an empty password, anyone could log in and run commands with the privileges of that account. Accounts with empty passwords should never be used in operational environments.

Remediation Shell script:   (show)

Complexity:low
Disruption:low
Strategy:disable
sed --follow-symlinks -i 's/\<nullok\>//g' /etc/pam.d/system-auth
Remediation Ansible snippet:   (show)

Complexity:low
Disruption:medium
Strategy:configure

- name: "Prevent Log In to Accounts With Empty Password"
  replace:
    dest: /etc/pam.d/system-auth
    regexp: 'nullok\s*'
    replace: ''

Verify All Account Password Hashes are Shadowed   [ref]rule

If any password hashes are stored in /etc/passwd (in the second field, instead of an x or *), the cause of this misconfiguration should be investigated. The account should have its password reset and the hash should be properly stored, or the account should be deleted entirely.

Rationale:

The hashes for all user account passwords should be stored in the file /etc/shadow and never in /etc/passwd, which is readable by all users.

All GIDs referenced in /etc/passwd must be defined in /etc/group   [ref]rule

Add a group to the system for each GID referenced without a corresponding group.

Rationale:

If a user is assigned the Group Identifier (GID) of a group not existing on the system, and a group with the Gruop Identifier (GID) is subsequently created, the user may have unintended rights to any files associated with the group.

identifiers:  CCE-27503-2

references:  IA-2, 764, SRG-OS-000104-GPOS-00051, RHEL-07-020300, Req-8.5.a, 5.5.2

Set Password Expiration Parameters   [ref]group

The file /etc/login.defs controls several password-related settings. Programs such as passwd, su, and login consult /etc/login.defs to determine behavior with regard to password aging, expiration warnings, and length. See the man page login.defs(5) for more information.

Users should be forced to change their passwords, in order to decrease the utility of compromised passwords. However, the need to change passwords often should be balanced against the risk that users will reuse or write down passwords if forced to change them too often. Forcing password changes every 90-360 days, depending on the environment, is recommended. Set the appropriate value as PASS_MAX_DAYS and apply it to existing accounts with the -M flag.

The PASS_MIN_DAYS (-m) setting prevents password changes for 7 days after the first change, to discourage password cycling. If you use this setting, train users to contact an administrator for an emergency password change in case a new password becomes compromised. The PASS_WARN_AGE (-W) setting gives users 7 days of warnings at login time that their passwords are about to expire.

For example, for each existing human user USER, expiration parameters could be adjusted to a 180 day maximum password age, 7 day minimum password age, and 7 day warning period with the following command:

$ sudo chage -M 180 -m 7 -W 7 USER

contains 2 rules
contains 2 rules

Protect Accounts by Configuring PAM   [ref]group

PAM, or Pluggable Authentication Modules, is a system which implements modular authentication for Linux programs. PAM provides a flexible and configurable architecture for authentication, and it should be configured to minimize exposure to unnecessary risk. This section contains guidance on how to accomplish that.

PAM is implemented as a set of shared objects which are loaded and invoked whenever an application wishes to authenticate a user. Typically, the application must be running as root in order to take advantage of PAM, because PAM's modules often need to be able to access sensitive stores of account information, such as /etc/shadow. Traditional privileged network listeners (e.g. sshd) or SUID programs (e.g. sudo) already meet this requirement. An SUID root application, userhelper, is provided so that programs which are not SUID or privileged themselves can still take advantage of PAM.

PAM looks in the directory /etc/pam.d for application-specific configuration information. For instance, if the program login attempts to authenticate a user, then PAM's libraries follow the instructions in the file /etc/pam.d/login to determine what actions should be taken.

One very important file in /etc/pam.d is /etc/pam.d/system-auth. This file, which is included by many other PAM configuration files, defines 'default' system authentication measures. Modifying this file is a good way to make far-reaching authentication changes, for instance when implementing a centralized authentication service.

warning  Be careful when making changes to PAM's configuration files. The syntax for these files is complex, and modifications can have unexpected consequences. The default configurations shipped with applications should be sufficient for most users.
warning  Running authconfig or system-config-authentication will re-write the PAM configuration files, destroying any manually made changes and replacing them with a series of system defaults. One reference to the configuration file syntax can be found at http://www.kernel.org/pub/linux/libs/pam/Linux-PAM-html/sag-configuration-file.html .
contains 19 rules

Set Password Quality Requirements   [ref]group

The default pam_pwquality PAM module provides strength checking for passwords. It performs a number of checks, such as making sure passwords are not similar to dictionary words, are of at least a certain length, are not the previous password reversed, and are not simply a change of case from the previous password. It can also require passwords to be in certain character classes. The pam_pwquality module is the preferred way of configuring password requirements.

The pam_cracklib PAM module can also provide strength checking for passwords as the pam_pwquality module. It performs a number of checks, such as making sure passwords are not similar to dictionary words, are of at least a certain length, are not the previous password reversed, and are not simply a change of case from the previous password. It can also require passwords to be in certain character classes.

The man pages pam_pwquality(8) and pam_cracklib(8) provide information on the capabilities and configuration of each.

contains 10 rules

Set Password Quality Requirements with pam_pwquality   [ref]group

The pam_pwquality PAM module can be configured to meet requirements for a variety of policies.

For example, to configure pam_pwquality to require at least one uppercase character, lowercase character, digit, and other (special) character, make sure that pam_pwquality exists in /etc/pam.d/system-auth:

password    requisite     pam_pwquality.so try_first_pass local_users_only retry=3 authtok_type=
If no such line exists, add one as the first line of the password section in /etc/pam.d/system-auth. Next, modify the settings in /etc/security/pwquality.conf to match the following:
difok = 4
minlen = 14
dcredit = -1
ucredit = -1
lcredit = -1
ocredit = -1
maxrepeat = 3
The arguments can be modified to ensure compliance with your organization's security policy. Discussion of each parameter follows.

warning  Note that the password quality requirements are not enforced for the root account for some reason.
contains 10 rules

Set Password Retry Prompts Permitted Per-Session   [ref]rule

To configure the number of retry prompts that are permitted per-session:

Edit the pam_pwquality.so statement in /etc/pam.d/system-auth to show retry=3, or a lower value if site policy is more restrictive.

The DoD requirement is a maximum of 3 prompts per session.

Rationale:

Setting the password retry prompts that are permitted on a per-session basis to a low value requires some software, such as SSH, to re-connect. This can slow down and draw additional attention to some types of password-guessing attacks. Note that this is different from account lockout, which is provided by the pam_faillock module.

identifiers:  CCE-27160-1

references:  CM-6(b), IA-5(c), 366, 6.3.2, SRG-OS-000480-GPOS-00225, RHEL-07-010119, 5.5.3

Remediation Shell script:   (show)

Complexity:low
Disruption:low
Strategy:disable

var_password_pam_retry="3"

if grep -q "retry=" /etc/pam.d/system-auth; then   
	sed -i --follow-symlinks "s/\(retry *= *\).*/\1$var_password_pam_retry/" /etc/pam.d/system-auth
else
	sed -i --follow-symlinks "/pam_pwquality.so/ s/$/ retry=$var_password_pam_retry/" /etc/pam.d/system-auth
fi

Set Password Maximum Consecutive Repeating Characters   [ref]rule

The pam_pwquality module's maxrepeat parameter controls requirements for consecutive repeating characters. When set to a positive number, it will reject passwords which contain more than that number of consecutive characters. Modify the maxrepeat setting in /etc/security/pwquality.conf to equal 2 to prevent a run of (2 + 1) or more identical characters.

Rationale:

Use of a complex password helps to increase the time and resources required to compromise the password. Password complexity, or strength, is a measure of the effectiveness of a password in resisting attempts at guessing and brute-force attacks.

Password complexity is one factor of several that determines how long it takes to crack a password. The more complex the password, the greater the number of possible combinations that need to be tested before the password is compromised.

Passwords with excessive repeating characters may be more vulnerable to password-guessing attacks.

identifiers:  CCE-27333-4

references:  IA-5, IA-5(c), 195, SRG-OS-000072-GPOS-00040, RHEL-07-010180

Remediation Shell script:   (show)

Complexity:low
Disruption:low
Strategy:disable

var_password_pam_maxrepeat="2"

function replace_or_append {
  local config_file=$1
  local key=$2
  local value=$3
  local cce=$4
  local format=$5

  # Check sanity of the input
  if [ $# -lt "3" ]
  then
        echo "Usage: replace_or_append 'config_file_location' 'key_to_search' 'new_value'"
        echo
        echo "If symlinks need to be taken into account, add yes/no to the last argument"
        echo "to allow to 'follow_symlinks'."
        echo "Aborting."
        exit 1
  fi

  # Test if the config_file is a symbolic link. If so, use --follow-symlinks with sed.
  # Otherwise, regular sed command will do.
  if test -L $config_file; then
    sed_command="sed -i --follow-symlinks"
  else
    sed_command="sed -i"
  fi

  # Test that the cce arg is not empty or does not equal $CCENUM.
  # If $CCENUM exists, it means that there is no CCE assigned.
  if ! [ "x$cce" = x ] && [ "$cce" != '$CCENUM' ]; then
    cce="CCE-${cce}"
  else
    cce="CCE"
  fi

  # Strip any search characters in the key arg so that the key can be replaced without
  # adding any search characters to the config file.
  stripped_key=$(sed "s/[\^=\$,;+]*//g" <<< $key)

  # If there is no print format specified in the last arg, use the default format.
  if ! [ "x$format" = x ] ; then
    printf -v formatted_output "$format" $stripped_key $value
  else
    formatted_output="$stripped_key = $value"
  fi

  # If the key exists, change it. Otherwise, add it to the config_file.
  if `grep -qi $key $config_file` ; then
    $sed_command "s/$key.*/$formatted_output/g" $config_file
  else
    # \n is precaution for case where file ends without trailing newline
    echo -e "\n# Per $cce: Set $formatted_output in $config_file" >> $config_file
    echo -e "$formatted_output" >> $config_file
  fi

}

replace_or_append '/etc/security/pwquality.conf' '^maxrepeat' $var_password_pam_maxrepeat 'CCE-27333-4' '%s = %s'

Set Password to Maximum of Consecutive Repeating Characters from Same Character Class   [ref]rule

The pam_pwquality module's maxclassrepeat parameter controls requirements for consecutive repeating characters from the same character class. When set to a positive number, it will reject passwords which contain more than that number of consecutive characters from the same character class. Modify the maxclassrepeat setting in /etc/security/pwquality.conf to equal 4 to prevent a run of (4 + 1) or more identical characters.

Rationale:

Use of a complex password helps to increase the time and resources required to comrpomise the password. Password complexity, or strength, is a measure of the effectiveness of a password in resisting attempts at guessing and brute-force attacks.
Password complexity is one factor of several that determines how long it takes to crack a password. The more complex a password, the greater the number of possible combinations that need to be tested before the password is compromised.

identifiers:  CCE-27512-3

references:  IA-5, IA-5(c), 195, SRG-OS-000072-GPOS-00040, RHEL-07-010190

Remediation Shell script:   (show)

Complexity:low
Disruption:low
Strategy:enable

var_password_pam_maxclassrepeat="4"

function replace_or_append {
  local config_file=$1
  local key=$2
  local value=$3
  local cce=$4
  local format=$5

  # Check sanity of the input
  if [ $# -lt "3" ]
  then
        echo "Usage: replace_or_append 'config_file_location' 'key_to_search' 'new_value'"
        echo
        echo "If symlinks need to be taken into account, add yes/no to the last argument"
        echo "to allow to 'follow_symlinks'."
        echo "Aborting."
        exit 1
  fi

  # Test if the config_file is a symbolic link. If so, use --follow-symlinks with sed.
  # Otherwise, regular sed command will do.
  if test -L $config_file; then
    sed_command="sed -i --follow-symlinks"
  else
    sed_command="sed -i"
  fi

  # Test that the cce arg is not empty or does not equal $CCENUM.
  # If $CCENUM exists, it means that there is no CCE assigned.
  if ! [ "x$cce" = x ] && [ "$cce" != '$CCENUM' ]; then
    cce="CCE-${cce}"
  else
    cce="CCE"
  fi

  # Strip any search characters in the key arg so that the key can be replaced without
  # adding any search characters to the config file.
  stripped_key=$(sed "s/[\^=\$,;+]*//g" <<< $key)

  # If there is no print format specified in the last arg, use the default format.
  if ! [ "x$format" = x ] ; then
    printf -v formatted_output "$format" $stripped_key $value
  else
    formatted_output="$stripped_key = $value"
  fi

  # If the key exists, change it. Otherwise, add it to the config_file.
  if `grep -qi $key $config_file` ; then
    $sed_command "s/$key.*/$formatted_output/g" $config_file
  else
    # \n is precaution for case where file ends without trailing newline
    echo -e "\n# Per $cce: Set $formatted_output in $config_file" >> $config_file
    echo -e "$formatted_output" >> $config_file
  fi

}

replace_or_append '/etc/security/pwquality.conf' '^maxclassrepeat' $var_password_pam_maxclassrepeat 'CCE-27512-3' '%s = %s'

Set Password Strength Minimum Digit Characters   [ref]rule

The pam_pwquality module's dcredit parameter controls requirements for usage of digits in a password. When set to a negative number, any password will be required to contain that many digits. When set to a positive number, pam_pwquality will grant +1 additional length credit for each digit. Modify the dcredit setting in /etc/security/pwquality.conf to require the use of a digit in passwords.

Rationale:

Use of a complex password helps to increase the time and resources required to compromise the password. Password complexity, or strength, is a measure of the effectiveness of a password in resisting attempts at guessing and brute-force attacks.

Password complexity is one factor of several that determines how long it takes to crack a password. The more complex the password, the greater the number of possble combinations that need to be tested before the password is compromised. Requiring digits makes password guessing attacks more difficult by ensuring a larger search space.

identifiers:  CCE-27214-6

references:  IA-5(1)(a), IA-5(b), IA-5(c), 194, 194, SRG-OS-000071-GPOS-00039, Req-8.2.3, 6.3.2, RHEL-07-010140

Remediation Shell script:   (show)

Complexity:low
Disruption:low
Strategy:disable

var_password_pam_dcredit="-1"

function replace_or_append {
  local config_file=$1
  local key=$2
  local value=$3
  local cce=$4
  local format=$5

  # Check sanity of the input
  if [ $# -lt "3" ]
  then
        echo "Usage: replace_or_append 'config_file_location' 'key_to_search' 'new_value'"
        echo
        echo "If symlinks need to be taken into account, add yes/no to the last argument"
        echo "to allow to 'follow_symlinks'."
        echo "Aborting."
        exit 1
  fi

  # Test if the config_file is a symbolic link. If so, use --follow-symlinks with sed.
  # Otherwise, regular sed command will do.
  if test -L $config_file; then
    sed_command="sed -i --follow-symlinks"
  else
    sed_command="sed -i"
  fi

  # Test that the cce arg is not empty or does not equal $CCENUM.
  # If $CCENUM exists, it means that there is no CCE assigned.
  if ! [ "x$cce" = x ] && [ "$cce" != '$CCENUM' ]; then
    cce="CCE-${cce}"
  else
    cce="CCE"
  fi

  # Strip any search characters in the key arg so that the key can be replaced without
  # adding any search characters to the config file.
  stripped_key=$(sed "s/[\^=\$,;+]*//g" <<< $key)

  # If there is no print format specified in the last arg, use the default format.
  if ! [ "x$format" = x ] ; then
    printf -v formatted_output "$format" $stripped_key $value
  else
    formatted_output="$stripped_key = $value"
  fi

  # If the key exists, change it. Otherwise, add it to the config_file.
  if `grep -qi $key $config_file` ; then
    $sed_command "s/$key.*/$formatted_output/g" $config_file
  else
    # \n is precaution for case where file ends without trailing newline
    echo -e "\n# Per $cce: Set $formatted_output in $config_file" >> $config_file
    echo -e "$formatted_output" >> $config_file
  fi

}

replace_or_append '/etc/security/pwquality.conf' '^dcredit' $var_password_pam_dcredit 'CCE-27214-6' '%s = %s'

Set Password Minimum Length   [ref]rule

The pam_pwquality module's minlen parameter controls requirements for minimum characters required in a password. Add minlen=15 after pam_pwquality to set minimum password length requirements.

Rationale:

The shorter the password, the lower the number of possible combinations that need to be tested before the password is compromised.
Password complexity, or strength, is a measure of the effectiveness of a password in resisting attempts at guessing and brute-force attacks. Password length is one factor of several that helps to determine strength and how long it takes to crack a password. Use of more characters in a password helps to exponentially increase the time and/or resources required to compromose the password.

identifiers:  CCE-27293-0

references:  IA-5(1)(a), 205, SRG-OS-000078-GPOS-00046, Req-8.2.3, 6.3.2, RHEL-07-010280

Remediation Shell script:   (show)

Complexity:low
Disruption:low
Strategy:disable

var_password_pam_minlen="15"

function replace_or_append {
  local config_file=$1
  local key=$2
  local value=$3
  local cce=$4
  local format=$5

  # Check sanity of the input
  if [ $# -lt "3" ]
  then
        echo "Usage: replace_or_append 'config_file_location' 'key_to_search' 'new_value'"
        echo
        echo "If symlinks need to be taken into account, add yes/no to the last argument"
        echo "to allow to 'follow_symlinks'."
        echo "Aborting."
        exit 1
  fi

  # Test if the config_file is a symbolic link. If so, use --follow-symlinks with sed.
  # Otherwise, regular sed command will do.
  if test -L $config_file; then
    sed_command="sed -i --follow-symlinks"
  else
    sed_command="sed -i"
  fi

  # Test that the cce arg is not empty or does not equal $CCENUM.
  # If $CCENUM exists, it means that there is no CCE assigned.
  if ! [ "x$cce" = x ] && [ "$cce" != '$CCENUM' ]; then
    cce="CCE-${cce}"
  else
    cce="CCE"
  fi

  # Strip any search characters in the key arg so that the key can be replaced without
  # adding any search characters to the config file.
  stripped_key=$(sed "s/[\^=\$,;+]*//g" <<< $key)

  # If there is no print format specified in the last arg, use the default format.
  if ! [ "x$format" = x ] ; then
    printf -v formatted_output "$format" $stripped_key $value
  else
    formatted_output="$stripped_key = $value"
  fi

  # If the key exists, change it. Otherwise, add it to the config_file.
  if `grep -qi $key $config_file` ; then
    $sed_command "s/$key.*/$formatted_output/g" $config_file
  else
    # \n is precaution for case where file ends without trailing newline
    echo -e "\n# Per $cce: Set $formatted_output in $config_file" >> $config_file
    echo -e "$formatted_output" >> $config_file
  fi

}

replace_or_append '/etc/security/pwquality.conf' '^minlen' $var_password_pam_minlen 'CCE-27293-0' '%s = %s'

Set Password Strength Minimum Uppercase Characters   [ref]rule

The pam_pwquality module's ucredit= parameter controls requirements for usage of uppercase letters in a password. When set to a negative number, any password will be required to contain that many uppercase characters. When set to a positive number, pam_pwquality will grant +1 additional length credit for each uppercase character. Modify the ucredit setting in /etc/security/pwquality.conf to require the use of an uppercase character in passwords.

Rationale:

Use of a complex password helps to increase the time and resources reuiqred to compromise the password. Password complexity, or strength, is a measure of the effectiveness of a password in resisting attempts at guessing and brute-force attacks.

Password complexity is one factor of several that determines how long it takes to crack a password. The more complex the password, the greater the number of possible combinations that need to be tested before the password is compromised.

identifiers:  CCE-27200-5

references:  IA-5(b), IA-5(c), IA-5(1)(a), 192, SRG-OS-000069-GPOS-00037, RHEL-07-010120, Req-8.2.3, 6.3.2

Remediation Shell script:   (show)

Complexity:low
Disruption:low
Strategy:enable

var_password_pam_ucredit="-1"

function replace_or_append {
  local config_file=$1
  local key=$2
  local value=$3
  local cce=$4
  local format=$5

  # Check sanity of the input
  if [ $# -lt "3" ]
  then
        echo "Usage: replace_or_append 'config_file_location' 'key_to_search' 'new_value'"
        echo
        echo "If symlinks need to be taken into account, add yes/no to the last argument"
        echo "to allow to 'follow_symlinks'."
        echo "Aborting."
        exit 1
  fi

  # Test if the config_file is a symbolic link. If so, use --follow-symlinks with sed.
  # Otherwise, regular sed command will do.
  if test -L $config_file; then
    sed_command="sed -i --follow-symlinks"
  else
    sed_command="sed -i"
  fi

  # Test that the cce arg is not empty or does not equal $CCENUM.
  # If $CCENUM exists, it means that there is no CCE assigned.
  if ! [ "x$cce" = x ] && [ "$cce" != '$CCENUM' ]; then
    cce="CCE-${cce}"
  else
    cce="CCE"
  fi

  # Strip any search characters in the key arg so that the key can be replaced without
  # adding any search characters to the config file.
  stripped_key=$(sed "s/[\^=\$,;+]*//g" <<< $key)

  # If there is no print format specified in the last arg, use the default format.
  if ! [ "x$format" = x ] ; then
    printf -v formatted_output "$format" $stripped_key $value
  else
    formatted_output="$stripped_key = $value"
  fi

  # If the key exists, change it. Otherwise, add it to the config_file.
  if `grep -qi $key $config_file` ; then
    $sed_command "s/$key.*/$formatted_output/g" $config_file
  else
    # \n is precaution for case where file ends without trailing newline
    echo -e "\n# Per $cce: Set $formatted_output in $config_file" >> $config_file
    echo -e "$formatted_output" >> $config_file
  fi

}

replace_or_append '/etc/security/pwquality.conf' '^ucredit' $var_password_pam_ucredit 'CCE-27200-5' '%s = %s'

Set Password Strength Minimum Special Characters   [ref]rule

The pam_pwquality module's ocredit= parameter controls requirements for usage of special (or "other") characters in a password. When set to a negative number, any password will be required to contain that many special characters. When set to a positive number, pam_pwquality will grant +1 additional length credit for each special character. Modify the ocredit setting in /etc/security/pwquality.conf to equal -1 to require use of a special character in passwords.

Rationale:

Use of a complex password helps to increase the time and resources required to compromise the password. Password complexity, or strength, is a measure of the effectiveness of a password in resisting attempts at guessing and brute-force attacks.

Password complexity is one factor of several that determines how long it takes to crack a password. The more complex the password, the greater the number of possble combinations that need to be tested before the password is compromised. Requiring a minimum number of special characters makes password guessing attacks more difficult by ensuring a larger search space.

identifiers:  CCE-27360-7

references:  IA-5(b), IA-5(c), IA-5(1)(a), 1619, SRG-OS-000266-GPOS-00101, RHEL-07-010150

Remediation Shell script:   (show)

Complexity:low
Disruption:low
Strategy:disable

var_password_pam_ocredit="-1"

function replace_or_append {
  local config_file=$1
  local key=$2
  local value=$3
  local cce=$4
  local format=$5

  # Check sanity of the input
  if [ $# -lt "3" ]
  then
        echo "Usage: replace_or_append 'config_file_location' 'key_to_search' 'new_value'"
        echo
        echo "If symlinks need to be taken into account, add yes/no to the last argument"
        echo "to allow to 'follow_symlinks'."
        echo "Aborting."
        exit 1
  fi

  # Test if the config_file is a symbolic link. If so, use --follow-symlinks with sed.
  # Otherwise, regular sed command will do.
  if test -L $config_file; then
    sed_command="sed -i --follow-symlinks"
  else
    sed_command="sed -i"
  fi

  # Test that the cce arg is not empty or does not equal $CCENUM.
  # If $CCENUM exists, it means that there is no CCE assigned.
  if ! [ "x$cce" = x ] && [ "$cce" != '$CCENUM' ]; then
    cce="CCE-${cce}"
  else
    cce="CCE"
  fi

  # Strip any search characters in the key arg so that the key can be replaced without
  # adding any search characters to the config file.
  stripped_key=$(sed "s/[\^=\$,;+]*//g" <<< $key)

  # If there is no print format specified in the last arg, use the default format.
  if ! [ "x$format" = x ] ; then
    printf -v formatted_output "$format" $stripped_key $value
  else
    formatted_output="$stripped_key = $value"
  fi

  # If the key exists, change it. Otherwise, add it to the config_file.
  if `grep -qi $key $config_file` ; then
    $sed_command "s/$key.*/$formatted_output/g" $config_file
  else
    # \n is precaution for case where file ends without trailing newline
    echo -e "\n# Per $cce: Set $formatted_output in $config_file" >> $config_file
    echo -e "$formatted_output" >> $config_file
  fi

}

replace_or_append '/etc/security/pwquality.conf' '^ocredit' $var_password_pam_ocredit 'CCE-27360-7' '%s = %s'

Set Password Strength Minimum Lowercase Characters   [ref]rule

The pam_pwquality module's lcredit parameter controls requirements for usage of lowercase letters in a password. When set to a negative number, any password will be required to contain that many lowercase characters. When set to a positive number, pam_pwquality will grant +1 additional length credit for each lowercase character. Modify the lcredit setting in /etc/security/pwquality.conf to require the use of a lowercase character in passwords.

Rationale:

Use of a complex password helps to increase the time and resources required to compromise the password. Password complexity, or strength, is a measure of the effectiveness of a password in resisting attempts at guessing and brute-force attacks.

Password complexity is one factor of several that determines how long it takes to crack a password. The more complex the password, the greater the number of possble combinations that need to be tested before the password is compromised. Requiring a minimum number of lowercase characters makes password guessing attacks more difficult by ensuring a larger search space.

identifiers:  CCE-27345-8

references:  IA-5(b), IA-5(c), IA-5(1)(a), 193, SRG-OS-000070-GPOS-00038, Req-8.2.3, RHEL-07-010130

Remediation Shell script:   (show)

Complexity:low
Disruption:low
Strategy:disable

var_password_pam_lcredit="-1"

function replace_or_append {
  local config_file=$1
  local key=$2
  local value=$3
  local cce=$4
  local format=$5

  # Check sanity of the input
  if [ $# -lt "3" ]
  then
        echo "Usage: replace_or_append 'config_file_location' 'key_to_search' 'new_value'"
        echo
        echo "If symlinks need to be taken into account, add yes/no to the last argument"
        echo "to allow to 'follow_symlinks'."
        echo "Aborting."
        exit 1
  fi

  # Test if the config_file is a symbolic link. If so, use --follow-symlinks with sed.
  # Otherwise, regular sed command will do.
  if test -L $config_file; then
    sed_command="sed -i --follow-symlinks"
  else
    sed_command="sed -i"
  fi

  # Test that the cce arg is not empty or does not equal $CCENUM.
  # If $CCENUM exists, it means that there is no CCE assigned.
  if ! [ "x$cce" = x ] && [ "$cce" != '$CCENUM' ]; then
    cce="CCE-${cce}"
  else
    cce="CCE"
  fi

  # Strip any search characters in the key arg so that the key can be replaced without
  # adding any search characters to the config file.
  stripped_key=$(sed "s/[\^=\$,;+]*//g" <<< $key)

  # If there is no print format specified in the last arg, use the default format.
  if ! [ "x$format" = x ] ; then
    printf -v formatted_output "$format" $stripped_key $value
  else
    formatted_output="$stripped_key = $value"
  fi

  # If the key exists, change it. Otherwise, add it to the config_file.
  if `grep -qi $key $config_file` ; then
    $sed_command "s/$key.*/$formatted_output/g" $config_file
  else
    # \n is precaution for case where file ends without trailing newline
    echo -e "\n# Per $cce: Set $formatted_output in $config_file" >> $config_file
    echo -e "$formatted_output" >> $config_file
  fi

}

replace_or_append '/etc/security/pwquality.conf' '^lcredit' $var_password_pam_lcredit 'CCE-27345-8' '%s = %s'

Set Password Strength Minimum Different Characters   [ref]rule

The pam_pwquality module's difok parameter sets the number of characters in a password that must not be present in and old password during a password change. Modify the difok setting in /etc/security/pwquality.conf to equal 8 to require differing characters when changing passwords.

Rationale:

Use of a complex password helps to increase the time and resources required to compromise the password. Password complexity, or strength, is a measure of the effectiveness of a password in resisting attempts at guessing and brute–force attacks.

Password complexity is one factor of several that determines how long it takes to crack a password. The more complex the password, the greater the number of possible combinations that need to be tested before the password is compromised.

Requiring a minimum number of different characters during password changes ensures that newly changed passwords should not resemble previously compromised ones. Note that passwords which are changed on compromised systems will still be compromised, however.

identifiers:  CCE-26631-2

references:  IA-5(b), IA-5(c), IA-5(1)(b), 195, SRG-OS-000072-GPOS-00040, RHEL-07-010160

Remediation Shell script:   (show)

Complexity:low
Disruption:medium
Reboot:true
Strategy:disable

var_password_pam_difok="8"

function replace_or_append {
  local config_file=$1
  local key=$2
  local value=$3
  local cce=$4
  local format=$5

  # Check sanity of the input
  if [ $# -lt "3" ]
  then
        echo "Usage: replace_or_append 'config_file_location' 'key_to_search' 'new_value'"
        echo
        echo "If symlinks need to be taken into account, add yes/no to the last argument"
        echo "to allow to 'follow_symlinks'."
        echo "Aborting."
        exit 1
  fi

  # Test if the config_file is a symbolic link. If so, use --follow-symlinks with sed.
  # Otherwise, regular sed command will do.
  if test -L $config_file; then
    sed_command="sed -i --follow-symlinks"
  else
    sed_command="sed -i"
  fi

  # Test that the cce arg is not empty or does not equal $CCENUM.
  # If $CCENUM exists, it means that there is no CCE assigned.
  if ! [ "x$cce" = x ] && [ "$cce" != '$CCENUM' ]; then
    cce="CCE-${cce}"
  else
    cce="CCE"
  fi

  # Strip any search characters in the key arg so that the key can be replaced without
  # adding any search characters to the config file.
  stripped_key=$(sed "s/[\^=\$,;+]*//g" <<< $key)

  # If there is no print format specified in the last arg, use the default format.
  if ! [ "x$format" = x ] ; then
    printf -v formatted_output "$format" $stripped_key $value
  else
    formatted_output="$stripped_key = $value"
  fi

  # If the key exists, change it. Otherwise, add it to the config_file.
  if `grep -qi $key $config_file` ; then
    $sed_command "s/$key.*/$formatted_output/g" $config_file
  else
    # \n is precaution for case where file ends without trailing newline
    echo -e "\n# Per $cce: Set $formatted_output in $config_file" >> $config_file
    echo -e "$formatted_output" >> $config_file
  fi

}

replace_or_append '/etc/security/pwquality.conf' '^difok' $var_password_pam_difok 'CCE-26631-2' '%s = %s'

Set Password Strength Minimum Different Categories   [ref]rule

The pam_pwquality module's minclass parameter controls requirements for usage of different character classes, or types, of character that must exist in a password before it is considered valid. For example, setting this value to three (3) requires that any password must have characters from at least three different categories in order to be approved. The default value is zero (0), meaning there are no required classes. There are four categories available:

* Upper-case characters
* Lower-case characters
* Digits
* Special characters (for example, punctuation)
Modify the minclass setting in /etc/security/pwquality.conf entry to require 4 differing categories of characters when changing passwords.

Rationale:

Use of a complex password helps to increase the time and resources required to compromise the password. Password complexity, or strength, is a measure of the effectiveness of a password in resisting attempts at guessing and brute-force attacks.

Password complexity is one factor of several that determines how long it takes to crack a password. The more complex the password, the greater the number of possible combinations that need to be tested before the password is compromised.

Requiring a minimum number of character categories makes password guessing attacks more difficult by ensuring a larger search space.

identifiers:  CCE-27115-5

references:  IA-5, 195, SRG-OS-000072-GPOS-00040, RHEL-07-010170

Remediation Shell script:   (show)

Complexity:low
Disruption:medium
Reboot:true
Strategy:disable

var_password_pam_minclass="4"

function replace_or_append {
  local config_file=$1
  local key=$2
  local value=$3
  local cce=$4
  local format=$5

  # Check sanity of the input
  if [ $# -lt "3" ]
  then
        echo "Usage: replace_or_append 'config_file_location' 'key_to_search' 'new_value'"
        echo
        echo "If symlinks need to be taken into account, add yes/no to the last argument"
        echo "to allow to 'follow_symlinks'."
        echo "Aborting."
        exit 1
  fi

  # Test if the config_file is a symbolic link. If so, use --follow-symlinks with sed.
  # Otherwise, regular sed command will do.
  if test -L $config_file; then
    sed_command="sed -i --follow-symlinks"
  else
    sed_command="sed -i"
  fi

  # Test that the cce arg is not empty or does not equal $CCENUM.
  # If $CCENUM exists, it means that there is no CCE assigned.
  if ! [ "x$cce" = x ] && [ "$cce" != '$CCENUM' ]; then
    cce="CCE-${cce}"
  else
    cce="CCE"
  fi

  # Strip any search characters in the key arg so that the key can be replaced without
  # adding any search characters to the config file.
  stripped_key=$(sed "s/[\^=\$,;+]*//g" <<< $key)

  # If there is no print format specified in the last arg, use the default format.
  if ! [ "x$format" = x ] ; then
    printf -v formatted_output "$format" $stripped_key $value
  else
    formatted_output="$stripped_key = $value"
  fi

  # If the key exists, change it. Otherwise, add it to the config_file.
  if `grep -qi $key $config_file` ; then
    $sed_command "s/$key.*/$formatted_output/g" $config_file
  else
    # \n is precaution for case where file ends without trailing newline
    echo -e "\n# Per $cce: Set $formatted_output in $config_file" >> $config_file
    echo -e "$formatted_output" >> $config_file
  fi

}

replace_or_append '/etc/security/pwquality.conf' '^minclass' $var_password_pam_minclass 'CCE-27115-5' '%s = %s'

Set Lockouts for Failed Password Attempts   [ref]group

The pam_faillock PAM module provides the capability to lock out user accounts after a number of failed login attempts. Its documentation is available in /usr/share/doc/pam-VERSION/txts/README.pam_faillock.

warning  Locking out user accounts presents the risk of a denial-of-service attack. The lockout policy must weigh whether the risk of such a denial-of-service attack outweighs the benefits of thwarting password guessing attacks.
contains 5 rules

Set Deny For Failed Password Attempts   [ref]rule

To configure the system to lock out accounts after a number of incorrect login attempts using pam_faillock.so, modify the content of both /etc/pam.d/system-auth and /etc/pam.d/password-auth as follows:

  • add the following line immediately before the pam_unix.so statement in the AUTH section:
    auth required pam_faillock.so preauth silent deny=3 unlock_time=604800 fail_interval=900
  • add the following line immediately after the pam_unix.so statement in the AUTH section:
    auth [default=die] pam_faillock.so authfail deny=3 unlock_time=604800 fail_interval=900
  • add the following line immediately before the pam_unix.so statement in the ACCOUNT section:
    account required pam_faillock.so

Rationale:

Locking out user accounts after a number of incorrect attempts prevents direct password guessing attacks.

Remediation Shell script:   (show)

Complexity:low
Disruption:low
Strategy:disable

var_accounts_passwords_pam_faillock_deny="3"

AUTH_FILES[0]="/etc/pam.d/system-auth"
AUTH_FILES[1]="/etc/pam.d/password-auth"

# This script fixes absence of pam_faillock.so in PAM stack or the
# absense of deny=[0-9]+ in pam_faillock.so arguments
# When inserting auth pam_faillock.so entries,
# the entry with preauth argument will be added before pam_unix.so module
# and entry with authfail argument will be added before pam_deny.so module.

# The placement of pam_faillock.so entries will not be changed
# if they are already present

for pamFile in "${AUTH_FILES[@]}"
do
	
	# pam_faillock.so already present?
	if grep -q "^auth.*pam_faillock.so.*" $pamFile; then

		# pam_faillock.so present, deny directive present?
		if grep -q "^auth.*[default=die].*pam_faillock.so.*authfail.*deny=" $pamFile; then

			# both pam_faillock.so & deny present, just correct deny directive value
			sed -i --follow-symlinks "s/\(^auth.*required.*pam_faillock.so.*preauth.*silent.*\)\(deny *= *\).*/\1\2$var_accounts_passwords_pam_faillock_deny/" $pamFile
			sed -i --follow-symlinks "s/\(^auth.*[default=die].*pam_faillock.so.*authfail.*\)\(deny *= *\).*/\1\2$var_accounts_passwords_pam_faillock_deny/" $pamFile

		# pam_faillock.so present, but deny directive not yet
		else

			# append correct deny value to appropriate places
			sed -i --follow-symlinks "/^auth.*required.*pam_faillock.so.*preauth.*silent.*/ s/$/ deny=$var_accounts_passwords_pam_faillock_deny/" $pamFile
			sed -i --follow-symlinks "/^auth.*[default=die].*pam_faillock.so.*authfail.*/ s/$/ deny=$var_accounts_passwords_pam_faillock_deny/" $pamFile
		fi

	# pam_faillock.so not present yet
	else

		# insert pam_faillock.so preauth row with proper value of the 'deny' option before pam_unix.so
		sed -i --follow-symlinks "/^auth.*pam_unix.so.*/i auth        required      pam_faillock.so preauth silent deny=$var_accounts_passwords_pam_faillock_deny" $pamFile
		# insert pam_faillock.so authfail row with proper value of the 'deny' option before pam_deny.so, after all modules which determine authentication outcome.
		sed -i --follow-symlinks "/^auth.*pam_deny.so.*/i auth        [default=die] pam_faillock.so authfail deny=$var_accounts_passwords_pam_faillock_deny" $pamFile
	fi

	# add pam_faillock.so into account phase
	if ! grep -q "^account.*required.*pam_faillock.so" $pamFile; then
		sed -i --follow-symlinks "/^account.*required.*pam_unix.so/i account     required      pam_faillock.so" $pamFile
	fi
done

Set Lockout Time For Failed Password Attempts   [ref]rule

To configure the system to lock out accounts after a number of incorrect login attempts and require an administrator to unlock the account using pam_faillock.so, modify the content of both /etc/pam.d/system-auth and /etc/pam.d/password-auth as follows:

  • add the following line immediately before the pam_unix.so statement in the AUTH section:
    auth required pam_faillock.so preauth silent deny=3 unlock_time=604800 fail_interval=900
  • add the following line immediately after the pam_unix.so statement in the AUTH section:
    auth [default=die] pam_faillock.so authfail deny=3 unlock_time=604800 fail_interval=900
  • add the following line immediately before the pam_unix.so statement in the ACCOUNT section:
    account required pam_faillock.so

Rationale:

Locking out user accounts after a number of incorrect attempts prevents direct password guessing attacks. Ensuring that an administrator is involved in unlocking locked accounts draws appropriate attention to such situations.

Remediation Shell script:   (show)

Complexity:low
Disruption:low
Strategy:disable

var_accounts_passwords_pam_faillock_unlock_time="604800"

AUTH_FILES[0]="/etc/pam.d/system-auth"
AUTH_FILES[1]="/etc/pam.d/password-auth"

for pamFile in "${AUTH_FILES[@]}"
do
	
	# pam_faillock.so already present?
	if grep -q "^auth.*pam_faillock.so.*" $pamFile; then

		# pam_faillock.so present, unlock_time directive present?
		if grep -q "^auth.*[default=die].*pam_faillock.so.*authfail.*unlock_time=" $pamFile; then

			# both pam_faillock.so & unlock_time present, just correct unlock_time directive value
			sed -i --follow-symlinks "s/\(^auth.*required.*pam_faillock.so.*preauth.*silent.*\)\(unlock_time *= *\).*/\1\2$var_accounts_passwords_pam_faillock_unlock_time/" $pamFile
			sed -i --follow-symlinks "s/\(^auth.*[default=die].*pam_faillock.so.*authfail.*\)\(unlock_time *= *\).*/\1\2$var_accounts_passwords_pam_faillock_unlock_time/" $pamFile

		# pam_faillock.so present, but unlock_time directive not yet
		else

			# append correct unlock_time value to appropriate places
			sed -i --follow-symlinks "/^auth.*required.*pam_faillock.so.*preauth.*silent.*/ s/$/ unlock_time=$var_accounts_passwords_pam_faillock_unlock_time/" $pamFile
			sed -i --follow-symlinks "/^auth.*[default=die].*pam_faillock.so.*authfail.*/ s/$/ unlock_time=$var_accounts_passwords_pam_faillock_unlock_time/" $pamFile
		fi

	# pam_faillock.so not present yet
	else

		# insert pam_faillock.so preauth & authfail rows with proper value of the 'unlock_time' option
		sed -i --follow-symlinks "/^auth.*sufficient.*pam_unix.so.*/i auth        required      pam_faillock.so preauth silent unlock_time=$var_accounts_passwords_pam_faillock_unlock_time" $pamFile
		sed -i --follow-symlinks "/^auth.*sufficient.*pam_unix.so.*/a auth        [default=die] pam_faillock.so authfail unlock_time=$var_accounts_passwords_pam_faillock_unlock_time" $pamFile
		sed -i --follow-symlinks "/^account.*required.*pam_unix.so/i account     required      pam_faillock.so" $pamFile
	fi
done

Configure the root Account for Failed Password Attempts   [ref]rule

To configure the system to lock out the root account after a number of incorrect login attempts using pam_faillock.so, modify the content of both /etc/pam.d/system-auth and /etc/pam.d/password-auth as follows:

  • Modify the following line in the AUTH section to add even_deny_root:
    auth required pam_faillock.so preauth silent even_deny_root deny=3 unlock_time=604800 fail_interval=900
  • Modify the following line in the AUTH section to add even_deny_root:
    auth [default=die] pam_faillock.so authfail even_deny_root deny=3 unlock_time=604800 fail_interval=900

Rationale:

By limiting the number of failed logon attempts, the risk of unauthorized system access via user password guessing, otherwise known as brute-forcing, is reduced. Limits are imposed by locking the account.

Remediation Shell script:   (show)

Complexity:low
Disruption:low
Strategy:disable

if [ $( grep -c "auth.*required.*pam_faillock.so.*even_deny_root" /etc/pam.d/system-auth ) -eq 0 ]; then
        BEGINNING_TXT=$( cat /etc/pam.d/system-auth | grep "auth.*required.*pam_faillock.so" | sed -e 's/[]\/$*.^|[]/\\&/g' )
	sed -i --follow-symlinks "s/$BEGINNING_TXT/$BEGINNING_TXT even_deny_root/" /etc/pam.d/system-auth
fi

if [ $( grep -c "auth.*default.*die.*pam_faillock.so.*even_deny_root" /etc/pam.d/system-auth ) -eq 0 ]; then
        BEGINNING_TXT=$( cat /etc/pam.d/system-auth | grep "auth.*default.*die.*pam_faillock.so"  | sed -e 's/[]\/$*.^|[]/\\&/g' )
	sed -i --follow-symlinks "s/$BEGINNING_TXT/$BEGINNING_TXT even_deny_root/" /etc/pam.d/system-auth
fi

Set Interval For Counting Failed Password Attempts   [ref]rule

Utilizing pam_faillock.so, the fail_interval directive configures the system to lock out an accounts after a number of incorrect login attempts within a specified time period. Modify the content of both /etc/pam.d/system-auth and /etc/pam.d/password-auth as follows:

  • Add the following line immediately before the pam_unix.so statement in the AUTH section:
    auth required pam_faillock.so preauth silent deny=3 unlock_time=604800 fail_interval=900
  • Add the following line immediately after the pam_unix.so statement in the AUTH section:
    auth [default=die] pam_faillock.so authfail deny=3 unlock_time=604800 fail_interval=900
  • Add the following line immediately before the pam_unix.so statement in the ACCOUNT section:
    account required pam_faillock.so

Rationale:

By limiting the number of failed logon attempts the risk of unauthorized system access via user password guessing, otherwise known as brute-forcing, is reduced. Limits are imposed by locking the account.

Remediation Shell script:   (show)

Complexity:low
Disruption:low
Strategy:disable

var_accounts_passwords_pam_faillock_fail_interval="900"

AUTH_FILES[0]="/etc/pam.d/system-auth"
AUTH_FILES[1]="/etc/pam.d/password-auth"

for pamFile in "${AUTH_FILES[@]}"
do
	
	# pam_faillock.so already present?
	if grep -q "^auth.*pam_faillock.so.*" $pamFile; then

		# pam_faillock.so present, 'fail_interval' directive present?
		if grep -q "^auth.*[default=die].*pam_faillock.so.*authfail.*fail_interval=" $pamFile; then

			# both pam_faillock.so & 'fail_interval' present, just correct 'fail_interval' directive value
			sed -i --follow-symlinks "s/\(^auth.*required.*pam_faillock.so.*preauth.*silent.*\)\(fail_interval *= *\).*/\1\2$var_accounts_passwords_pam_faillock_fail_interval/" $pamFile
			sed -i --follow-symlinks "s/\(^auth.*[default=die].*pam_faillock.so.*authfail.*\)\(fail_interval *= *\).*/\1\2$var_accounts_passwords_pam_faillock_fail_interval/" $pamFile

		# pam_faillock.so present, but 'fail_interval' directive not yet
		else

			# append correct 'fail_interval' value to appropriate places
			sed -i --follow-symlinks "/^auth.*required.*pam_faillock.so.*preauth.*silent.*/ s/$/ fail_interval=$var_accounts_passwords_pam_faillock_fail_interval/" $pamFile
			sed -i --follow-symlinks "/^auth.*[default=die].*pam_faillock.so.*authfail.*/ s/$/ fail_interval=$var_accounts_passwords_pam_faillock_fail_interval/" $pamFile
		fi

	# pam_faillock.so not present yet
	else

		# insert pam_faillock.so preauth & authfail rows with proper value of the 'fail_interval' option
		sed -i --follow-symlinks "/^auth.*sufficient.*pam_unix.so.*/i auth        required      pam_faillock.so preauth silent fail_interval=$var_accounts_passwords_pam_faillock_fail_interval" $pamFile
		sed -i --follow-symlinks "/^auth.*sufficient.*pam_unix.so.*/a auth        [default=die] pam_faillock.so authfail fail_interval=$var_accounts_passwords_pam_faillock_fail_interval" $pamFile
		sed -i --follow-symlinks "/^account.*required.*pam_unix.so/i account     required      pam_faillock.so" $pamFile
	fi
done

Limit Password Reuse   [ref]rule

Do not allow users to reuse recent passwords. This can be accomplished by using the remember option for the pam_unix or pam_pwhistory PAM modules.

In the file /etc/pam.d/system-auth, append remember=5 to the line which refers to the pam_unix.so or pam_pwhistory.somodule, as shown below:

  • for the pam_unix.so case:
    password sufficient pam_unix.so ...existing_options... remember=5
  • for the pam_pwhistory.so case:
    password requisite pam_pwhistory.so ...existing_options... remember=5
The DoD STIG requirement is 5 passwords.

Rationale:

Preventing re-use of previous passwords helps ensure that a compromised password is not re-used by a user.

Remediation Shell script:   (show)

Complexity:low
Disruption:low
Strategy:disable

var_password_pam_unix_remember="5"

if grep -q "remember=" /etc/pam.d/system-auth; then   
	sed -i --follow-symlinks "s/\(^password.*sufficient.*pam_unix.so.*\)\(\(remember *= *\)[^ $]*\)/\1remember=$var_password_pam_unix_remember/" /etc/pam.d/system-auth
else
	sed -i --follow-symlinks "/^password[[:space:]]\+sufficient[[:space:]]\+pam_unix.so/ s/$/ remember=$var_password_pam_unix_remember/" /etc/pam.d/system-auth
fi

Set Password Hashing Algorithm   [ref]group

The system's default algorithm for storing password hashes in /etc/shadow is SHA-512. This can be configured in several locations.

contains 3 rules

Set PAM's Password Hashing Algorithm   [ref]rule

The PAM system service can be configured to only store encrypted representations of passwords. In /etc/pam.d/system-auth, the password section of the file controls which PAM modules execute during a password change. Set the pam_unix.so module in the password section to include the argument sha512, as shown below:

password    sufficient    pam_unix.so sha512 other arguments...

This will help ensure when local users change their passwords, hashes for the new passwords will be generated using the SHA-512 algorithm. This is the default.

Rationale:

Passwords need to be protected at all times, and encryption is the standard method for protecting passwords. If passwords are not encrypted, they can be plainly read (i.e., clear text) and easily compromised. Passwords that are encrypted with a weak algorithm are no more protected than if they are kepy in plain text.

This setting ensures user and group account administration utilities are configured to store only encrypted representations of passwords. Additionally, the crypt_style configuration option ensures the use of a strong hashing algorithm that makes password cracking attacks more difficult.

Remediation Shell script:   (show)

Complexity:low
Disruption:low
Strategy:disable
if ! grep -q "^password.*sufficient.*pam_unix.so.*sha512" /etc/pam.d/system-auth; then   
	sed -i --follow-symlinks "/^password.*sufficient.*pam_unix.so/ s/$/ sha512/" /etc/pam.d/system-auth
fi

Set Password Hashing Algorithm in /etc/login.defs   [ref]rule

In /etc/login.defs, add or correct the following line to ensure the system will use SHA-512 as the hashing algorithm:

ENCRYPT_METHOD SHA512

Rationale:

Passwords need to be protected at all times, and encryption is the standard method for protecting passwords. If passwords are not encrypted, they can be plainly read (i.e., clear text) and easily compromised. Passwords that are encrypted with a weak algorithm are no more protected than if they are kept in plain text.

Using a stronger hashing algorithm makes password cracking attacks more difficult.

Remediation Shell script:   (show)

Complexity:low
Disruption:low
Strategy:disable
if grep --silent ^ENCRYPT_METHOD /etc/login.defs ; then
	sed -i 's/^ENCRYPT_METHOD.*/ENCRYPT_METHOD SHA512/g' /etc/login.defs
else
	echo "" >> /etc/login.defs
	echo "ENCRYPT_METHOD SHA512" >> /etc/login.defs
fi

Set Password Hashing Algorithm in /etc/libuser.conf   [ref]rule

In /etc/libuser.conf, add or correct the following line in its [defaults] section to ensure the system will use the SHA-512 algorithm for password hashing:

crypt_style = sha512

Rationale:

Passwords need to be protected at all times, and encryption is the standard method for protecting passwords. If passwords are not encrypted, they can be plainly read (i.e., clear text) and easily compromised. Passwords that are encrypted with a weak algorithm are no more protected than if they are kepy in plain text.

This setting ensures user and group account administration utilities are configured to store only encrypted representations of passwords. Additionally, the crypt_style configuration option ensures the use of a strong hashing algorithm that makes password cracking attacks more difficult.

Secure Session Configuration Files for Login Accounts   [ref]group

When a user logs into a Unix account, the system configures the user's session by reading a number of files. Many of these files are located in the user's home directory, and may have weak permissions as a result of user error or misconfiguration. If an attacker can modify or even read certain types of account configuration information, they can often gain full access to the affected user's account. Therefore, it is important to test and correct configuration file permissions for interactive accounts, particularly those of privileged users such as root or system administrators.

contains 4 rules

Ensure that Users Have Sensible Umask Values   [ref]group

The umask setting controls the default permissions for the creation of new files. With a default umask setting of 077, files and directories created by users will not be readable by any other user on the system. Users who wish to make specific files group- or world-readable can accomplish this by using the chmod command. Additionally, users can make all their files readable to their group by default by setting a umask of 027 in their shell configuration files. If default per-user groups exist (that is, if every user has a default group whose name is the same as that user's username and whose only member is the user), then it may even be safe for users to select a umask of 007, making it very easy to intentionally share files with groups of which the user is a member.

contains 1 rule

Set Interactive Session Timeout   [ref]rule

Setting the TMOUT option in /etc/profile ensures that all user sessions will terminate based on inactivity. The TMOUT setting in /etc/profile should read as follows:

TMOUT=600

Rationale:

Terminating an idle session within a short time period reduces the window of opportunity for unauthorized personnel to take control of a management session enabled on the console or console port that has been left unattended.

identifiers:  CCE-27557-8

references:  AC-12, SC-10, 1133, 0361, SRG-OS-000163-GPOS-00072, RHEL-07-040160, 3.1.11

Remediation Shell script:   (show)

Complexity:low
Disruption:low
Strategy:disable

var_accounts_tmout="600"

if grep --silent ^TMOUT /etc/profile ; then
        sed -i "s/^TMOUT.*/TMOUT=$var_accounts_tmout/g" /etc/profile
else
        echo -e "\n# Set TMOUT to $var_accounts_tmout per security requirements" >> /etc/profile
        echo "TMOUT=$var_accounts_tmout" >> /etc/profile
fi

Ensure the Logon Failure Delay is Set Correctly in login.defs   [ref]rule

To ensure the logon failure delay controlled by /etc/login.defs is set properly, add or correct the FAIL_DELAY setting in /etc/login.defs to read as follows:

FAIL_DELAY 4

Rationale:

Increasing the time between a failed authentication attempt and re-prompting to enter credentials helps to slow a single-threaded brute force attack.

identifiers:  CCE-80352-8

references:  CM-6(b), 366, SRG-OS-000480-GPOS-00226, RHEL-07-010430

Protect Physical Console Access   [ref]group

It is impossible to fully protect a system from an attacker with physical access, so securing the space in which the system is located should be considered a necessary step. However, there are some steps which, if taken, make it more difficult for an attacker to quickly or undetectably modify a system from its console.

contains 8 rules

Set Boot Loader Password   [ref]group

During the boot process, the boot loader is responsible for starting the execution of the kernel and passing options to it. The boot loader allows for the selection of different kernels - possibly on different partitions or media. The default Red Hat Enterprise Linux boot loader for x86 systems is called GRUB2. Options it can pass to the kernel include single-user mode, which provides root access without any authentication, and the ability to disable SELinux. To prevent local users from modifying the boot parameters and endangering security, protect the boot loader configuration with a password and ensure its configuration file's permissions are set properly.

contains 2 rules

Set Boot Loader Password   [ref]rule

The grub2 boot loader should have a superuser account and password protection enabled to protect boot-time settings.

To do so, select a superuser account and password and add them into the /etc/grub.d/01_users configuration file.

Since plaintext passwords are a security risk, generate a hash for the pasword by running the following command:

$ grub2-mkpasswd-pbkdf2
When prompted, enter the password that was selected and insert the returned password hash into the /etc/grub.d/01_users configuration file immediately after the superuser account. (Use the output from grub2-mkpasswd-pbkdf2 as the value of password-hash):
password_pbkdf2 superusers-account password-hash
NOTE: It is recommended not to use common administrator account names like root, admin, or administrator for the grub2 superuser account.

To meet FISMA Moderate, the bootloader superuser account and password MUST differ from the root account and password. Once the superuser account and password have been added, update the grub.cfg file by running:
grub2-mkconfig -o /boot/grub2/grub.cfg
NOTE: Do NOT manually add the superuser account and password to the grub.cfg file as the grub2-mkconfig command overwrites this file.

Rationale:

Password protection on the boot loader configuration ensures users with physical access cannot trivially alter important bootloader settings. These include which kernel to use, and whether to enter single-user mode. For more information on how to configure the grub2 superuser account and password, please refer to

identifiers:  CCE-27309-4

references:  IA-2(1), IA-5(e), AC-3, 213, SRG-OS-000080-GPOS-00048, RHEL-07-010480, 1.5.3, 3.4.5

Set the UEFI Boot Loader Password   [ref]rule

The UEFI grub2 boot loader should have a superuser account and password protection enabled to protect boot-time settings.

To do so, select a superuser account and password and add them into the /etc/grub.d/01_users configuration file.

Since plaintext passwords are a security risk, generate a hash for the pasword by running the following command:

$ grub2-mkpasswd-pbkdf2
When prompted, enter the password that was selected and insert the returned password hash into the /etc/grub.d/01_users configuration file immediately after the superuser account. (Use the output from grub2-mkpasswd-pbkdf2 as the value of password-hash):
password_pbkdf2 superusers-account password-hash
NOTE: It is recommended not to use common administrator account names like root, admin, or administrator for the grub2 superuser account.

To meet FISMA Moderate, the bootloader superuser account and password MUST differ from the root account and password. Once the superuser account and password have been added, update the grub.cfg file by running:
grub2-mkconfig -o /boot/efi/EFI/redhat/grub.cfg
NOTE: Do NOT manually add the superuser account and password to the grub.cfg file as the grub2-mkconfig command overwrites this file.

Rationale:

Password protection on the boot loader configuration ensures users with physical access cannot trivially alter important bootloader settings. These include which kernel to use, and whether to enter single-user mode. For more information on how to configure the grub2 superuser account and password, please refer to

identifiers:  CCE-80354-4

references:  AC-3, 213, SRG-OS-000080-GPOS-00048, RHEL-07-010490, 3.4.5

Configure Screen Locking   [ref]group

When a user must temporarily leave an account logged-in, screen locking should be employed to prevent passersby from abusing the account. User education and training is particularly important for screen locking to be effective, and policies can be implemented to reinforce this.

Automatic screen locking is only meant as a safeguard for those cases where a user forgot to lock the screen.

contains 2 rules

Configure Console Screen Locking   [ref]group

A console screen locking mechanism is provided in the screen package, which is not installed by default.

contains 1 rule

Install the screen Package   [ref]rule

To enable console screen locking, install the screen package:

$ sudo yum install screen
Instruct users to begin new terminal sessions with the following command:
$ screen
The console can now be locked with the following key combination:
ctrl+a x

Rationale:

A session time-out lock is a temporary action taken when a user stops work and moves away from the immediate physical vicinity of the information system but des not logout because of the temporary nature of the absence. Rather than relying on the user to manually lock their operation system session prior to vacating the vicinity, operating systems need to be able to identify when a user's session has idled and take action to initiate the session lock.

The screen package allows for a session lock to be implemented and configured.

identifiers:  CCE-27351-6

references:  AC-11(a), 57, SRG-OS-000029-GPOS-00010, RHEL-07-010090, 3.1.10

Remediation Shell script:   (show)

Complexity:low
Disruption:low
Strategy:enable

function package_command {

# Load function arguments into local variables
local package_operation=$1
local package=$2

# Check sanity of the input
if [ $# -ne "2" ]
then
  echo "Usage: package_command 'install/uninstall' 'rpm_package_name"
  echo "Aborting."
  exit 1
fi

# If dnf is installed, use dnf; otherwise, use yum
if [ -f "/usr/bin/dnf" ] ; then
  install_util="/usr/bin/dnf"
else
  install_util="/usr/bin/yum"
fi

if [ "$package_operation" != 'remove' ] ; then
  # If the rpm is not installed, install the rpm
  if ! /bin/rpm -q --quiet $package; then
    $install_util -y $package_operation $package
  fi
else
  # If the rpm is installed, uninstall the rpm
  if /bin/rpm -q --quiet $package; then
    $install_util -y $package_operation $package
  fi
fi

}

package_command install screen
Remediation Ansible snippet:   (show)

Complexity:low
Disruption:low
Strategy:enable
- name: Ensure screen is installed
  package:
    name="{{item}}"
    state=present
  with_items:
    - screen
Remediation Puppet snippet:   (show)

Complexity:low
Disruption:low
Strategy:enable
include install_screen

class install_screen {
  package { 'screen':
    ensure => 'installed',
  }
}
Remediation script:   (show)

Complexity:low
Disruption:low
Strategy:enable

package -add=screen
contains 1 rule

Enable Smart Card Login   [ref]rule

To enable smart card authentication, consult the documentation at:

For guidance on enabling SSH to authenticate against a Common Access Card (CAC), consult documentation at:

Rationale:

Smart card login provides two-factor authentication stronger than that provided by a username and password combination. Smart cards leverage PKI (public key infrastructure) in order to provide and verify credentials.

Remediation Shell script:   (show)

Complexity:low
Disruption:low
Strategy:disable


# Install required packages

function package_command {

# Load function arguments into local variables
local package_operation=$1
local package=$2

# Check sanity of the input
if [ $# -ne "2" ]
then
  echo "Usage: package_command 'install/uninstall' 'rpm_package_name"
  echo "Aborting."
  exit 1
fi

# If dnf is installed, use dnf; otherwise, use yum
if [ -f "/usr/bin/dnf" ] ; then
  install_util="/usr/bin/dnf"
else
  install_util="/usr/bin/yum"
fi

if [ "$package_operation" != 'remove' ] ; then
  # If the rpm is not installed, install the rpm
  if ! /bin/rpm -q --quiet $package; then
    $install_util -y $package_operation $package
  fi
else
  # If the rpm is installed, uninstall the rpm
  if /bin/rpm -q --quiet $package; then
    $install_util -y $package_operation $package
  fi
fi

}

package_command install esc
package_command install pam_pkcs11

# Enable pcscd.socket systemd activation socket

function service_command {

# Load function arguments into local variables
local service_state=$1
local service=$2
local xinetd=$(echo $3 | cut -d'=' -f2)

# Check sanity of the input
if [ $# -lt "2" ]
then
  echo "Usage: service_command 'enable/disable' 'service_name.service'"
  echo
  echo "To enable or disable xinetd services add \'xinetd=service_name\'"
  echo "as the last argument"
  echo "Aborting."
  exit 1
fi

# If systemctl is installed, use systemctl command; otherwise, use the service/chkconfig commands
if [ -f "/usr/bin/systemctl" ] ; then
  service_util="/usr/bin/systemctl"
else
  service_util="/sbin/service"
  chkconfig_util="/sbin/chkconfig"
fi

# If disable is not specified in arg1, set variables to enable services.
# Otherwise, variables are to be set to disable services.
if [ "$service_state" != 'disable' ] ; then
  service_state="enable"
  service_operation="start"
  chkconfig_state="on"
else
  service_state="disable"
  service_operation="stop"
  chkconfig_state="off"
fi

# If chkconfig_util is not empty, use chkconfig/service commands.
if ! [ "x$chkconfig_util" = x ] ; then
  $service_util $service $service_operation
  $chkconfig_util --level 0123456 $service $chkconfig_state
else
  $service_util $service_operation $service
  $service_util $service_state $service
fi

# Test if local variable xinetd is empty using non-bashism.
# If empty, then xinetd is not being used.
if ! [ "x$xinetd" = x ] ; then
  grep -qi disable /etc/xinetd.d/$xinetd && \

  if ! [ "$service_operation" != 'disable' ] ; then
    sed -i "s/disable.*/disable         = no/gI" /etc/xinetd.d/$xinetd
  else
    sed -i "s/disable.*/disable         = yes/gI" /etc/xinetd.d/$xinetd
  fi
fi

}

service_command enable pcscd.socket

# Configure the expected /etc/pam.d/system-auth{,-ac} settings directly
#
# The code below will configure system authentication in the way smart card
# logins will be enabled, but also user login(s) via other method to be allowed
#
# NOTE: It is not possible to use the 'authconfig' command to perform the
#       remediation for us, because call of 'authconfig' would discard changes
#       for other remediations (see RH BZ#1357019 for details)
#
#	Therefore we need to configure the necessary settings directly.
#

# Define system-auth config location
SYSTEM_AUTH_CONF="/etc/pam.d/system-auth"
# Define expected 'pam_env.so' row in $SYSTEM_AUTH_CONF
PAM_ENV_SO="auth.*required.*pam_env.so"

# Define 'pam_succeed_if.so' row to be appended past $PAM_ENV_SO row into $SYSTEM_AUTH_CONF
SYSTEM_AUTH_PAM_SUCCEED="\
auth        \[success=1 default=ignore\] pam_succeed_if.so service notin \
login:gdm:xdm:kdm:xscreensaver:gnome-screensaver:kscreensaver quiet use_uid"
# Define 'pam_pkcs11.so' row to be appended past $SYSTEM_AUTH_PAM_SUCCEED
# row into SYSTEM_AUTH_CONF file
SYSTEM_AUTH_PAM_PKCS11="\
auth        \[success=done authinfo_unavail=ignore ignore=ignore default=die\] \
pam_pkcs11.so nodebug"

# Define smartcard-auth config location
SMARTCARD_AUTH_CONF="/etc/pam.d/smartcard-auth"
# Define 'pam_pkcs11.so' auth section to be appended past $PAM_ENV_SO into $SMARTCARD_AUTH_CONF
SMARTCARD_AUTH_SECTION="\
auth        [success=done ignore=ignore default=die] pam_pkcs11.so wait_for_card card_only"
# Define expected 'pam_permit.so' row in $SMARTCARD_AUTH_CONF
PAM_PERMIT_SO="account.*required.*pam_permit.so"
# Define 'pam_pkcs11.so' password section
SMARTCARD_PASSWORD_SECTION="\
password    required      pam_pkcs11.so"

# First Correct the SYSTEM_AUTH_CONF configuration
if ! grep -q 'pam_pkcs11.so' "$SYSTEM_AUTH_CONF"
then
	# Append (expected) pam_succeed_if.so row past the pam_env.so into SYSTEM_AUTH_CONF file
	sed -i --follow-symlinks -e '/^'"$PAM_ENV_SO"'/a '"$SYSTEM_AUTH_PAM_SUCCEED" "$SYSTEM_AUTH_CONF"
	# Append (expected) pam_pkcs11.so row past the pam_succeed_if.so into SYSTEM_AUTH_CONF file
	sed -i --follow-symlinks -e '/^'"$SYSTEM_AUTH_PAM_SUCCEED"'/a '"$SYSTEM_AUTH_PAM_PKCS11" "$SYSTEM_AUTH_CONF"
fi

# Then also correct the SMARTCARD_AUTH_CONF
if ! grep -q 'pam_pkcs11.so' "$SMARTCARD_AUTH_CONF"
then
	# Append (expected) SMARTCARD_AUTH_SECTION row past the pam_env.so into SMARTCARD_AUTH_CONF file
	sed -i --follow-symlinks -e '/^'"$PAM_ENV_SO"'/a '"$SMARTCARD_AUTH_SECTION" "$SMARTCARD_AUTH_CONF"
	# Append (expected) SMARTCARD_PASSWORD_SECTION row past the pam_permit.so into SMARTCARD_AUTH_CONF file
	sed -i --follow-symlinks -e '/^'"$PAM_PERMIT_SO"'/a '"$SMARTCARD_PASSWORD_SECTION" "$SMARTCARD_AUTH_CONF"
fi

# Perform /etc/pam_pkcs11/pam_pkcs11.conf settings below
# Define selected constants for later reuse
SP="[:space:]"
PAM_PKCS11_CONF="/etc/pam_pkcs11/pam_pkcs11.conf"

# Ensure OCSP is turned on in $PAM_PKCS11_CONF
# 1) First replace any occurrence of 'none' value of 'cert_policy' key setting with the correct configuration
sed -i "s/^[$SP]*cert_policy[$SP]\+=[$SP]\+none;/\t\tcert_policy = ca, ocsp_on, signature;/g" "$PAM_PKCS11_CONF"
# 2) Then append 'ocsp_on' value setting to each 'cert_policy' key in $PAM_PKCS11_CONF configuration line,
# which does not contain it yet
sed -i "/ocsp_on/! s/^[$SP]*cert_policy[$SP]\+=[$SP]\+\(.*\);/\t\tcert_policy = \1, ocsp_on;/" "$PAM_PKCS11_CONF"

Require Authentication for Single User Mode   [ref]rule

Single-user mode is intended as a system recovery method, providing a single user root access to the system by providing a boot option at startup. By default, no authentication is performed if single-user mode is selected.

By default, single-user mode is protected by requiring a password and is set in /usr/lib/systemd/system/rescue.service.

Rationale:

This prevents attackers with physical access from trivially bypassing security on the machine and gaining root access. Such accesses are further prevented by configuring the bootloader password.

identifiers:  CCE-27287-2

references:  IA-2(1), AC-3, 213, 3.1.1, 3.4.5

Remediation Shell script:   (show)

Complexity:low
Disruption:low
Strategy:disable
grep -q "^ExecStart=\-.*/sbin/sulogin" /usr/lib/systemd/system/rescue.service
if ! [ $? -eq 0 ]; then
    sed -i "s/ExecStart=-.*-c \"/&\/sbin\/sulogin; /g" /usr/lib/systemd/system/rescue.service
fi

Disable debug-shell SystemD Service   [ref]rule

SystemD's debug-shell service is intended to diagnose SystemD related boot issues with various systemctl commands. Once enabled and following a system reboot, the root shell will be available on tty9 which is access by pressing CTRL-ALT-F9. The debug-shell service should only be used for SystemD related issues and should otherwise be disabled.

By default, the debug-shell SystemD service is disabled. The debug-shell service can be disabled with the following command:

$ sudo systemctl disable debug-shell.service

Rationale:

This prevents attackers with physical access from trivially bypassing security on the machine through valid troubleshooting configurations and gaining root access when the system is rebooted.

identifiers:  CCE-80206-6

references:  3.4.5

Remediation Shell script:   (show)

Complexity:low
Disruption:low
Strategy:disable

function service_command {

# Load function arguments into local variables
local service_state=$1
local service=$2
local xinetd=$(echo $3 | cut -d'=' -f2)

# Check sanity of the input
if [ $# -lt "2" ]
then
  echo "Usage: service_command 'enable/disable' 'service_name.service'"
  echo
  echo "To enable or disable xinetd services add \'xinetd=service_name\'"
  echo "as the last argument"
  echo "Aborting."
  exit 1
fi

# If systemctl is installed, use systemctl command; otherwise, use the service/chkconfig commands
if [ -f "/usr/bin/systemctl" ] ; then
  service_util="/usr/bin/systemctl"
else
  service_util="/sbin/service"
  chkconfig_util="/sbin/chkconfig"
fi

# If disable is not specified in arg1, set variables to enable services.
# Otherwise, variables are to be set to disable services.
if [ "$service_state" != 'disable' ] ; then
  service_state="enable"
  service_operation="start"
  chkconfig_state="on"
else
  service_state="disable"
  service_operation="stop"
  chkconfig_state="off"
fi

# If chkconfig_util is not empty, use chkconfig/service commands.
if ! [ "x$chkconfig_util" = x ] ; then
  $service_util $service $service_operation
  $chkconfig_util --level 0123456 $service $chkconfig_state
else
  $service_util $service_operation $service
  $service_util $service_state $service
fi

# Test if local variable xinetd is empty using non-bashism.
# If empty, then xinetd is not being used.
if ! [ "x$xinetd" = x ] ; then
  grep -qi disable /etc/xinetd.d/$xinetd && \

  if ! [ "$service_operation" != 'disable' ] ; then
    sed -i "s/disable.*/disable         = no/gI" /etc/xinetd.d/$xinetd
  else
    sed -i "s/disable.*/disable         = yes/gI" /etc/xinetd.d/$xinetd
  fi
fi

}

service_command disable debug-shell
Remediation Ansible snippet:   (show)

Complexity:low
Disruption:low
Strategy:disable
- name: Disable service debug-shell
  service:
    name="{{item}}"
    enabled="no"
    state="stopped"
  with_items:
    - debug-shell

Disable Ctrl-Alt-Del Reboot Activation   [ref]rule

By default, SystemD will reboot the system if the Ctrl-Alt-Del key sequence is pressed.

To configure the system to ignore the Ctrl-Alt-Del key sequence from the command line instead of rebooting the system, do either of the following:

ln -sf /dev/null /etc/systemd/system/ctrl-alt-del.target
or
systemctl mask ctrl-alt-del.target


Do not simply delete the /usr/lib/systemd/system/ctrl-alt-del.service file, as this file may be restored during future system updates.

warning  Disabling the Ctrl-Alt-Del key sequence with SystemD DOES NOT disable the Ctrl-Alt-Del key sequence if running in graphical.target mode (e.g. in GNOME, KDE, etc.)! The Ctrl-Alt-Del key sequence will only be disabled if running in the non-graphical multi-user.target mode.
Rationale:

A locally logged-in user who presses Ctrl-Alt-Del, when at the console, can reboot the system. If accidentally pressed, as could happen in the case of mixed OS environment, this can create the risk of short-term loss of availability of systems due to unintentional reboot.

identifiers:  CCE-27511-5

references:  AC-6, 366, SRG-OS-000480-GPOS-00227, RHEL-07-020230, 3.4.5

Remediation Shell script:   (show)

Complexity:low
Disruption:low
Strategy:disable
# The process to disable ctrl+alt+del has changed in RHEL7. 
# Reference: https://access.redhat.com/solutions/1123873
ln -sf /dev/null /etc/systemd/system/ctrl-alt-del.target

Verify that Interactive Boot is Disabled   [ref]rule

Red Hat Enterprise Linux systems support an "interactive boot" option that can be used to prevent services from being started. On a Red Hat Enterprise Linux 7 system, interactive boot can be enabled by providing a 1, yes, true, or on value to the systemd.confirm_spawn kernel argument in /etc/default/grub. Remove any instance of

systemd.confirm_spawn=(1|yes|true|on)
from the kernel arguments in that file to disable interactive boot.

warning  The GRUB 2 configuration file, grub.cfg, is automatically updated each time a new kernel is installed. Note that any changes to /etc/default/grub require rebuilding the grub.cfg file. To update the GRUB 2 configuration file manually, use the
grub2-mkconfig -o
command as follows:
  • On BIOS-based machines, issue the following command as root:
    ~]# grub2-mkconfig -o /boot/grub2/grub.cfg
  • On UEFI-based machines, issue the following command as root:
    ~]# grub2-mkconfig -o /boot/efi/EFI/redhat/grub.cfg
Rationale:

Using interactive boot, the console user could disable auditing, firewalls, or other services, weakening system security.

identifiers:  CCE-27335-9

references:  SC-2, AC-3, 213, 3.1.2, 3.4.5

Remediation Shell script:   (show)

Complexity:low
Disruption:low
Strategy:disable

# Systemd confirm_spawn regex to search for and delete if found
CONFIRM_SPAWN_REGEX="systemd.confirm_spawn=\(1\|yes\|true\|on\)"

# Modify both the GRUB_CMDLINE_LINUX and GRUB_CMDLINE_LINUX_DEFAULT directives
for grubcmdline in "GRUB_CMDLINE_LINUX" "GRUB_CMDLINE_LINUX_DEFAULT"
do
  # Remove 'systemd.confirm_spawn' argument from /etc/default/grub if found
  if grep -q "^${grubcmdline}=\".*${CONFIRM_SPAWN_REGEX}.*\"" /etc/default/grub
  then
    # Remove all three possible occurrences of CONFIRM_SPAWN_REGEX:
    # At the start
    sed -i "s/\"${CONFIRM_SPAWN_REGEX} /\"/" /etc/default/grub
    # At the end
    sed -i "s/ ${CONFIRM_SPAWN_REGEX}\"$/\"/" /etc/default/grub
    # In the middle
    sed -i "s/ ${CONFIRM_SPAWN_REGEX}//" /etc/default/grub
  fi
done
# Remove 'systemd.confirm_spawn' kernel argument also from runtime settings
/sbin/grubby --update-kernel=ALL --remove-args="systemd.confirm_spawn"

Warning Banners for System Accesses   [ref]group

Each system should expose as little information about itself as possible.

System banners, which are typically displayed just before a login prompt, give out information about the service or the host's operating system. This might include the distribution name and the system kernel version, and the particular version of a network service. This information can assist intruders in gaining access to the system as it can reveal whether the system is running vulnerable software. Most network services can be configured to limit what information is displayed.

Many organizations implement security policies that require a system banner provide notice of the system's ownership, provide warning to unauthorized users, and remind authorized users of their consent to monitoring.

contains 3 rules
contains 2 rules

Enable GNOME3 Login Warning Banner   [ref]rule

In the default graphical environment, displaying a login warning banner in the GNOME Display Manager's login screen can be enabled on the login screen by setting banner-message-enable to true.

To enable, add or edit banner-message-enable to /etc/dconf/db/gdm.d/00-security-settings. For example:

[org/gnome/login-screen]
banner-message-enable=true
Once the setting has been added, add a lock to /etc/dconf/db/gdm.d/locks/00-security-settings-lock to prevent user modification. For example:
/org/gnome/login-screen/banner-message-enable
After the settings have been set, run dconf update. The banner text must also be set.

Rationale:

Display of a standardized and approved use notification before granting access to the operating system ensures privacy and security notification verbiage used is consistent with applicable federal laws, Executive Orders, directives, policies, regulations, standards, and guidance.

For U.S. Government systems, system use notifications are required only for access via login interfaces with human users and are not required when such human interfaces do not exist.

Modify the System Login Banner   [ref]rule

To configure the system login banner edit /etc/issue. Replace the default text with a message compliant with the local site policy or a legal disclaimer. The DoD required text is either:

You are accessing a U.S. Government (USG) Information System (IS) that is provided for USG-authorized use only. By using this IS (which includes any device attached to this IS), you consent to the following conditions:
-The USG routinely intercepts and monitors communications on this IS for purposes including, but not limited to, penetration testing, COMSEC monitoring, network operations and defense, personnel misconduct (PM), law enforcement (LE), and counterintelligence (CI) investigations.
-At any time, the USG may inspect and seize data stored on this IS.
-Communications using, or data stored on, this IS are not private, are subject to routine monitoring, interception, and search, and may be disclosed or used for any USG-authorized purpose.
-This IS includes security measures (e.g., authentication and access controls) to protect USG interests -- not for your personal benefit or privacy.
-Notwithstanding the above, using this IS does not constitute consent to PM, LE or CI investigative searching or monitoring of the content of privileged communications, or work product, related to personal representation or services by attorneys, psychotherapists, or clergy, and their assistants. Such communications and work product are private and confidential. See User Agreement for details.


OR:

I've read & consent to terms in IS user agreem't.

Rationale:

Display of a standardized and approved use notification before granting access to the operating system ensures privacy and security notification verbiage used is consistent with applicable federal laws, Executive Orders, directives, policies, regulations, standards, and guidance.

System use notifications are required only for access via login interfaces with human users and are not required when such human interfaces do not exist.

Remediation Shell script:   (show)

Complexity:low
Disruption:low
Strategy:disable

login_banner_text="You[\s\n]+are[\s\n]+accessing[\s\n]+a[\s\n]+U.S.[\s\n]+Government[\s\n]+\(USG\)[\s\n]+Information[\s\n]+System[\s\n]+\(IS\)[\s\n]+that[\s\n]+is[\s\n]+provided[\s\n]+for[\s\n]+USG-authorized[\s\n]+use[\s\n]+only.[\s\n]*By[\s\n]+using[\s\n]+this[\s\n]+IS[\s\n]+\(which[\s\n]+includes[\s\n]+any[\s\n]+device[\s\n]+attached[\s\n]+to[\s\n]+this[\s\n]+IS\),[\s\n]+you[\s\n]+consent[\s\n]+to[\s\n]+the[\s\n]+following[\s\n]+conditions\:[\s\n]*-[\s\n]*The[\s\n]+USG[\s\n]+routinely[\s\n]+intercepts[\s\n]+and[\s\n]+monitors[\s\n]+communications[\s\n]+on[\s\n]+this[\s\n]+IS[\s\n]+for[\s\n]+purposes[\s\n]+including,[\s\n]+but[\s\n]+not[\s\n]+limited[\s\n]+to,[\s\n]+penetration[\s\n]+testing,[\s\n]+COMSEC[\s\n]+monitoring,[\s\n]+network[\s\n]+operations[\s\n]+and[\s\n]+defense,[\s\n]+personnel[\s\n]+misconduct[\s\n]+\(PM\),[\s\n]+law[\s\n]+enforcement[\s\n]+\(LE\),[\s\n]+and[\s\n]+counterintelligence[\s\n]+\(CI\)[\s\n]+investigations.[\s\n]*-[\s\n]*At[\s\n]+any[\s\n]+time,[\s\n]+the[\s\n]+USG[\s\n]+may[\s\n]+inspect[\s\n]+and[\s\n]+seize[\s\n]+data[\s\n]+stored[\s\n]+on[\s\n]+this[\s\n]+IS.[\s\n]*-[\s\n]*Communications[\s\n]+using,[\s\n]+or[\s\n]+data[\s\n]+stored[\s\n]+on,[\s\n]+this[\s\n]+IS[\s\n]+are[\s\n]+not[\s\n]+private,[\s\n]+are[\s\n]+subject[\s\n]+to[\s\n]+routine[\s\n]+monitoring,[\s\n]+interception,[\s\n]+and[\s\n]+search,[\s\n]+and[\s\n]+may[\s\n]+be[\s\n]+disclosed[\s\n]+or[\s\n]+used[\s\n]+for[\s\n]+any[\s\n]+USG-authorized[\s\n]+purpose.[\s\n]*-[\s\n]*This[\s\n]+IS[\s\n]+includes[\s\n]+security[\s\n]+measures[\s\n]+\(e.g.,[\s\n]+authentication[\s\n]+and[\s\n]+access[\s\n]+controls\)[\s\n]+to[\s\n]+protect[\s\n]+USG[\s\n]+interests[\s\n]+--[\s\n]+not[\s\n]+for[\s\n]+your[\s\n]+personal[\s\n]+benefit[\s\n]+or[\s\n]+privacy.[\s\n]*-[\s\n]*Notwithstanding[\s\n]+the[\s\n]+above,[\s\n]+using[\s\n]+this[\s\n]+IS[\s\n]+does[\s\n]+not[\s\n]+constitute[\s\n]+consent[\s\n]+to[\s\n]+PM,[\s\n]+LE[\s\n]+or[\s\n]+CI[\s\n]+investigative[\s\n]+searching[\s\n]+or[\s\n]+monitoring[\s\n]+of[\s\n]+the[\s\n]+content[\s\n]+of[\s\n]+privileged[\s\n]+communications,[\s\n]+or[\s\n]+work[\s\n]+product,[\s\n]+related[\s\n]+to[\s\n]+personal[\s\n]+representation[\s\n]+or[\s\n]+services[\s\n]+by[\s\n]+attorneys,[\s\n]+psychotherapists,[\s\n]+or[\s\n]+clergy,[\s\n]+and[\s\n]+their[\s\n]+assistants.[\s\n]+Such[\s\n]+communications[\s\n]+and[\s\n]+work[\s\n]+product[\s\n]+are[\s\n]+private[\s\n]+and[\s\n]+confidential.[\s\n]+See[\s\n]+User[\s\n]+Agreement[\s\n]+for[\s\n]+details."

# There was a regular-expression matching various banners, needs to be expanded
expanded=$(echo "$login_banner_text" | sed 's/\[\\s\\n\][+*]/ /g;s/\\//g;s/[^-]- /\n\n-/g')
formatted=$(echo "$expanded" | fold -sw 80)

cat <<EOF >/etc/issue
$formatted
EOF

printf "\n" >> /etc/issue

Network Configuration and Firewalls   [ref]group

Most systems must be connected to a network of some sort, and this brings with it the substantial risk of network attack. This section discusses the security impact of decisions about networking which must be made when configuring a system.

This section also discusses firewalls, network access controls, and other network security frameworks, which allow system-level rules to be written that can limit an attackers' ability to connect to your system. These rules can specify that network traffic should be allowed or denied from certain IP addresses, hosts, and networks. The rules can also specify which of the system's network services are available to particular hosts or networks.

contains 20 rules

Kernel Parameters Which Affect Networking   [ref]group

The sysctl utility is used to set parameters which affect the operation of the Linux kernel. Kernel parameters which affect networking and have security implications are described here.

contains 9 rules

Network Parameters for Hosts Only   [ref]group

If the system is not going to be used as a router, then setting certain kernel parameters ensure that the host will not perform routing of network traffic.

contains 3 rules

Disable Kernel Parameter for Sending ICMP Redirects by Default   [ref]rule

To set the runtime status of the net.ipv4.conf.default.send_redirects kernel parameter, run the following command:

$ sudo sysctl -w net.ipv4.conf.default.send_redirects=0
If this is not the system's default value, add the following line to /etc/sysctl.conf:
net.ipv4.conf.default.send_redirects = 0

Rationale:

ICMP redirect messages are used by routers to inform hosts that a more direct route exists for a particular destination. These messages contain information from the system's route table possibly revealing portions of the network topology.
The ability to send ICMP redirects is only appropriate for systems acting as routers.

identifiers:  CCE-80156-3

references:  AC-4, CM-7, SC-5, SC-7, 366, 4.1.2, SRG-OS-000480-GPOS-00227, RHEL-07-040650, 5.10.1.1, 3.1.20

Remediation Shell script:   (show)

Complexity:low
Disruption:medium
Reboot:true
Strategy:disable


#
# Set runtime for net.ipv4.conf.default.send_redirects
#
/sbin/sysctl -q -n -w net.ipv4.conf.default.send_redirects=0

#
# If net.ipv4.conf.default.send_redirects present in /etc/sysctl.conf, change value to "0"
#	else, add "net.ipv4.conf.default.send_redirects = 0" to /etc/sysctl.conf
#

function replace_or_append {
  local config_file=$1
  local key=$2
  local value=$3
  local cce=$4
  local format=$5

  # Check sanity of the input
  if [ $# -lt "3" ]
  then
        echo "Usage: replace_or_append 'config_file_location' 'key_to_search' 'new_value'"
        echo
        echo "If symlinks need to be taken into account, add yes/no to the last argument"
        echo "to allow to 'follow_symlinks'."
        echo "Aborting."
        exit 1
  fi

  # Test if the config_file is a symbolic link. If so, use --follow-symlinks with sed.
  # Otherwise, regular sed command will do.
  if test -L $config_file; then
    sed_command="sed -i --follow-symlinks"
  else
    sed_command="sed -i"
  fi

  # Test that the cce arg is not empty or does not equal $CCENUM.
  # If $CCENUM exists, it means that there is no CCE assigned.
  if ! [ "x$cce" = x ] && [ "$cce" != '$CCENUM' ]; then
    cce="CCE-${cce}"
  else
    cce="CCE"
  fi

  # Strip any search characters in the key arg so that the key can be replaced without
  # adding any search characters to the config file.
  stripped_key=$(sed "s/[\^=\$,;+]*//g" <<< $key)

  # If there is no print format specified in the last arg, use the default format.
  if ! [ "x$format" = x ] ; then
    printf -v formatted_output "$format" $stripped_key $value
  else
    formatted_output="$stripped_key = $value"
  fi

  # If the key exists, change it. Otherwise, add it to the config_file.
  if `grep -qi $key $config_file` ; then
    $sed_command "s/$key.*/$formatted_output/g" $config_file
  else
    # \n is precaution for case where file ends without trailing newline
    echo -e "\n# Per $cce: Set $formatted_output in $config_file" >> $config_file
    echo -e "$formatted_output" >> $config_file
  fi

}

replace_or_append '/etc/sysctl.conf' '^net.ipv4.conf.default.send_redirects' '0' 'CCE-80156-3'

Disable Kernel Parameter for Sending ICMP Redirects for All Interfaces   [ref]rule

To set the runtime status of the net.ipv4.conf.all.send_redirects kernel parameter, run the following command:

$ sudo sysctl -w net.ipv4.conf.all.send_redirects=0
If this is not the system's default value, add the following line to /etc/sysctl.conf:
net.ipv4.conf.all.send_redirects = 0

Rationale:

ICMP redirect messages are used by routers to inform hosts that a more direct route exists for a particular destination. These messages contain information from the system's route table possibly revealing portions of the network topology.
The ability to send ICMP redirects is only appropriate for systems acting as routers.

identifiers:  CCE-80156-3

references:  AC-4, CM-7, SC-5(1), 366, 4.1.2, SRG-OS-000480-GPOS-00227, RHEL-07-040660, 5.10.1.1, 3.1.20

Remediation Shell script:   (show)

Complexity:low
Disruption:medium
Reboot:true
Strategy:disable


#
# Set runtime for net.ipv4.conf.all.send_redirects
#
/sbin/sysctl -q -n -w net.ipv4.conf.all.send_redirects=0

#
# If net.ipv4.conf.all.send_redirects present in /etc/sysctl.conf, change value to "0"
#	else, add "net.ipv4.conf.all.send_redirects = 0" to /etc/sysctl.conf
#

function replace_or_append {
  local config_file=$1
  local key=$2
  local value=$3
  local cce=$4
  local format=$5

  # Check sanity of the input
  if [ $# -lt "3" ]
  then
        echo "Usage: replace_or_append 'config_file_location' 'key_to_search' 'new_value'"
        echo
        echo "If symlinks need to be taken into account, add yes/no to the last argument"
        echo "to allow to 'follow_symlinks'."
        echo "Aborting."
        exit 1
  fi

  # Test if the config_file is a symbolic link. If so, use --follow-symlinks with sed.
  # Otherwise, regular sed command will do.
  if test -L $config_file; then
    sed_command="sed -i --follow-symlinks"
  else
    sed_command="sed -i"
  fi

  # Test that the cce arg is not empty or does not equal $CCENUM.
  # If $CCENUM exists, it means that there is no CCE assigned.
  if ! [ "x$cce" = x ] && [ "$cce" != '$CCENUM' ]; then
    cce="CCE-${cce}"
  else
    cce="CCE"
  fi

  # Strip any search characters in the key arg so that the key can be replaced without
  # adding any search characters to the config file.
  stripped_key=$(sed "s/[\^=\$,;+]*//g" <<< $key)

  # If there is no print format specified in the last arg, use the default format.
  if ! [ "x$format" = x ] ; then
    printf -v formatted_output "$format" $stripped_key $value
  else
    formatted_output="$stripped_key = $value"
  fi

  # If the key exists, change it. Otherwise, add it to the config_file.
  if `grep -qi $key $config_file` ; then
    $sed_command "s/$key.*/$formatted_output/g" $config_file
  else
    # \n is precaution for case where file ends without trailing newline
    echo -e "\n# Per $cce: Set $formatted_output in $config_file" >> $config_file
    echo -e "$formatted_output" >> $config_file
  fi

}

replace_or_append '/etc/sysctl.conf' '^net.ipv4.conf.all.send_redirects' '0' 'CCE-80156-3'

Disable Kernel Parameter for IP Forwarding   [ref]rule

To set the runtime status of the net.ipv4.ip_forward kernel parameter, run the following command:

$ sudo sysctl -w net.ipv4.ip_forward=0
If this is not the system's default value, add the following line to /etc/sysctl.conf:
net.ipv4.ip_forward = 0

Rationale:

Routing protocol daemons are typically used on routers to exchange network topology information with other routers. If this capability is used when not required, system network information may be unnecessarily transmitted across the network.

identifiers:  CCE-80157-1

references:  CM-7, SC-5, SC-32, 366, 4.1.1, SRG-OS-000480-GPOS-00227, RHEL-07-040740, 3.1.20

Remediation Shell script:   (show)

Complexity:low
Disruption:medium
Reboot:true
Strategy:disable


#
# Set runtime for net.ipv4.ip_forward
#
/sbin/sysctl -q -n -w net.ipv4.ip_forward=0

#
# If net.ipv4.ip_forward present in /etc/sysctl.conf, change value to "0"
#	else, add "net.ipv4.ip_forward = 0" to /etc/sysctl.conf
#

function replace_or_append {
  local config_file=$1
  local key=$2
  local value=$3
  local cce=$4
  local format=$5

  # Check sanity of the input
  if [ $# -lt "3" ]
  then
        echo "Usage: replace_or_append 'config_file_location' 'key_to_search' 'new_value'"
        echo
        echo "If symlinks need to be taken into account, add yes/no to the last argument"
        echo "to allow to 'follow_symlinks'."
        echo "Aborting."
        exit 1
  fi

  # Test if the config_file is a symbolic link. If so, use --follow-symlinks with sed.
  # Otherwise, regular sed command will do.
  if test -L $config_file; then
    sed_command="sed -i --follow-symlinks"
  else
    sed_command="sed -i"
  fi

  # Test that the cce arg is not empty or does not equal $CCENUM.
  # If $CCENUM exists, it means that there is no CCE assigned.
  if ! [ "x$cce" = x ] && [ "$cce" != '$CCENUM' ]; then
    cce="CCE-${cce}"
  else
    cce="CCE"
  fi

  # Strip any search characters in the key arg so that the key can be replaced without
  # adding any search characters to the config file.
  stripped_key=$(sed "s/[\^=\$,;+]*//g" <<< $key)

  # If there is no print format specified in the last arg, use the default format.
  if ! [ "x$format" = x ] ; then
    printf -v formatted_output "$format" $stripped_key $value
  else
    formatted_output="$stripped_key = $value"
  fi

  # If the key exists, change it. Otherwise, add it to the config_file.
  if `grep -qi $key $config_file` ; then
    $sed_command "s/$key.*/$formatted_output/g" $config_file
  else
    # \n is precaution for case where file ends without trailing newline
    echo -e "\n# Per $cce: Set $formatted_output in $config_file" >> $config_file
    echo -e "$formatted_output" >> $config_file
  fi

}

replace_or_append '/etc/sysctl.conf' '^net.ipv4.ip_forward' '0' 'CCE-80157-1'

Network Related Kernel Runtime Parameters for Hosts and Routers   [ref]group

Certain kernel parameters should be set for systems which are acting as either hosts or routers to improve the system's ability defend against certain types of IPv4 protocol attacks.

contains 6 rules

Configure Kernel Parameter for Accepting Source-Routed Packets for All Interfaces   [ref]rule

To set the runtime status of the net.ipv4.conf.all.accept_source_route kernel parameter, run the following command:

$ sudo sysctl -w net.ipv4.conf.all.accept_source_route=0
If this is not the system's default value, add the following line to /etc/sysctl.conf:
net.ipv4.conf.all.accept_source_route = 0

Rationale:

Source-routed packets allow the source of the packet to suggest routers forward the packet along a different path than configured on the router, which can be used to bypass network security measures. This requirement applies only to the forwarding of source-routerd traffic, such as when IPv4 forwarding is enabled and the system is functioning as a router.

Accepting source-routed packets in the IPv4 protocol has few legitimate uses. It should be disabled unless it is absolutely required.

identifiers:  CCE-27434-0

references:  AC-4, CM-7, SC-5, 366, SRG-OS-000480-GPOS-00227, RHEL-07-040610, 4.2.1, 3.1.20

Remediation Shell script:   (show)

Complexity:low
Disruption:medium
Reboot:true
Strategy:disable

sysctl_net_ipv4_conf_all_accept_source_route_value="0"

#
# Set runtime for net.ipv4.conf.all.accept_source_route
#
/sbin/sysctl -q -n -w net.ipv4.conf.all.accept_source_route=$sysctl_net_ipv4_conf_all_accept_source_route_value

#
# If net.ipv4.conf.all.accept_source_route present in /etc/sysctl.conf, change value to appropriate value
#	else, add "net.ipv4.conf.all.accept_source_route = value" to /etc/sysctl.conf
#

function replace_or_append {
  local config_file=$1
  local key=$2
  local value=$3
  local cce=$4
  local format=$5

  # Check sanity of the input
  if [ $# -lt "3" ]
  then
        echo "Usage: replace_or_append 'config_file_location' 'key_to_search' 'new_value'"
        echo
        echo "If symlinks need to be taken into account, add yes/no to the last argument"
        echo "to allow to 'follow_symlinks'."
        echo "Aborting."
        exit 1
  fi

  # Test if the config_file is a symbolic link. If so, use --follow-symlinks with sed.
  # Otherwise, regular sed command will do.
  if test -L $config_file; then
    sed_command="sed -i --follow-symlinks"
  else
    sed_command="sed -i"
  fi

  # Test that the cce arg is not empty or does not equal $CCENUM.
  # If $CCENUM exists, it means that there is no CCE assigned.
  if ! [ "x$cce" = x ] && [ "$cce" != '$CCENUM' ]; then
    cce="CCE-${cce}"
  else
    cce="CCE"
  fi

  # Strip any search characters in the key arg so that the key can be replaced without
  # adding any search characters to the config file.
  stripped_key=$(sed "s/[\^=\$,;+]*//g" <<< $key)

  # If there is no print format specified in the last arg, use the default format.
  if ! [ "x$format" = x ] ; then
    printf -v formatted_output "$format" $stripped_key $value
  else
    formatted_output="$stripped_key = $value"
  fi

  # If the key exists, change it. Otherwise, add it to the config_file.
  if `grep -qi $key $config_file` ; then
    $sed_command "s/$key.*/$formatted_output/g" $config_file
  else
    # \n is precaution for case where file ends without trailing newline
    echo -e "\n# Per $cce: Set $formatted_output in $config_file" >> $config_file
    echo -e "$formatted_output" >> $config_file
  fi

}

replace_or_append '/etc/systcl.conf' '^net.ipv4.conf.all.accept_source_route' '$sysctl_net_ipv4_conf_all_accept_source_route_value' 'CCE-27434-0'

Configure Kernel Parameter for Accepting ICMP Redirects for All Interfaces   [ref]rule

To set the runtime status of the net.ipv4.conf.all.accept_redirects kernel parameter, run the following command:

$ sudo sysctl -w net.ipv4.conf.all.accept_redirects=0
If this is not the system's default value, add the following line to /etc/sysctl.conf:
net.ipv4.conf.all.accept_redirects = 0

Rationale:

ICMP redirect messages are used by routers to inform hosts that a more direct route exists for a particular destination. These messages modify the host's route table and are unauthenticated. An illicit ICMP redirect message could result in a man-in-the-middle attack.
This feature of the IPv4 protocol has few legitimate uses. It should be disabled unless absolutely required.

identifiers:  CCE-80158-9

references:  CM-6(d), CM-7, SC-5, 366, 1503, 1551, 4.2.2, SRG-OS-000480-GPOS-00227, RHEL-07-040641, 5.10.1.1, 3.1.20

Remediation Shell script:   (show)

Complexity:low
Disruption:medium
Reboot:true
Strategy:disable

sysctl_net_ipv4_conf_all_accept_redirects_value="0"

#
# Set runtime for net.ipv4.conf.all.accept_redirects
#
/sbin/sysctl -q -n -w net.ipv4.conf.all.accept_redirects=$sysctl_net_ipv4_conf_all_accept_redirects_value

#
# If net.ipv4.conf.all.accept_redirects present in /etc/sysctl.conf, change value to appropriate value
#	else, add "net.ipv4.conf.all.accept_redirects = value" to /etc/sysctl.conf
#

function replace_or_append {
  local config_file=$1
  local key=$2
  local value=$3
  local cce=$4
  local format=$5

  # Check sanity of the input
  if [ $# -lt "3" ]
  then
        echo "Usage: replace_or_append 'config_file_location' 'key_to_search' 'new_value'"
        echo
        echo "If symlinks need to be taken into account, add yes/no to the last argument"
        echo "to allow to 'follow_symlinks'."
        echo "Aborting."
        exit 1
  fi

  # Test if the config_file is a symbolic link. If so, use --follow-symlinks with sed.
  # Otherwise, regular sed command will do.
  if test -L $config_file; then
    sed_command="sed -i --follow-symlinks"
  else
    sed_command="sed -i"
  fi

  # Test that the cce arg is not empty or does not equal $CCENUM.
  # If $CCENUM exists, it means that there is no CCE assigned.
  if ! [ "x$cce" = x ] && [ "$cce" != '$CCENUM' ]; then
    cce="CCE-${cce}"
  else
    cce="CCE"
  fi

  # Strip any search characters in the key arg so that the key can be replaced without
  # adding any search characters to the config file.
  stripped_key=$(sed "s/[\^=\$,;+]*//g" <<< $key)

  # If there is no print format specified in the last arg, use the default format.
  if ! [ "x$format" = x ] ; then
    printf -v formatted_output "$format" $stripped_key $value
  else
    formatted_output="$stripped_key = $value"
  fi

  # If the key exists, change it. Otherwise, add it to the config_file.
  if `grep -qi $key $config_file` ; then
    $sed_command "s/$key.*/$formatted_output/g" $config_file
  else
    # \n is precaution for case where file ends without trailing newline
    echo -e "\n# Per $cce: Set $formatted_output in $config_file" >> $config_file
    echo -e "$formatted_output" >> $config_file
  fi

}

replace_or_append '/etc/systcl.conf' '^net.ipv4.conf.all.accept_redirects' '$sysctl_net_ipv4_conf_all_accept_redirects_value' 'CCE-80158-9'

Configure Kernel Parameter for Accepting Source-Routed Packets By Default   [ref]rule

To set the runtime status of the net.ipv4.conf.default.accept_source_route kernel parameter, run the following command:

$ sudo sysctl -w net.ipv4.conf.default.accept_source_route=0
If this is not the system's default value, add the following line to /etc/sysctl.conf:
net.ipv4.conf.default.accept_source_route = 0

Rationale:

Source-routed packets allow the source of the packet to suggest routers forward the packet along a different path than configured on the router, which can be used to bypass network security measures.
Accepting source-routed packets in the IPv4 protocol has few legitimate uses. It should be disabled unless it is absolutely required, such as when IPv4 forwarding is enabled and the system is legitimately functioning as a router.

identifiers:  CCE-80162-1

references:  AC-4, CM-7, SC-5, SC-7, 366, 1551, SRG-OS-000480-GPOS-00227, RHEL-07-040620, 4.2.1, 5.10.1.1, 3.1.20

Remediation Shell script:   (show)

Complexity:low
Disruption:medium
Reboot:true
Strategy:disable

sysctl_net_ipv4_conf_default_accept_source_route_value="0"

#
# Set runtime for net.ipv4.conf.default.accept_source_route
#
/sbin/sysctl -q -n -w net.ipv4.conf.default.accept_source_route=$sysctl_net_ipv4_conf_default_accept_source_route_value

#
# If net.ipv4.conf.default.accept_source_route present in /etc/sysctl.conf, change value to appropriate value
#	else, add "net.ipv4.conf.default.accept_source_route = value" to /etc/sysctl.conf
#

function replace_or_append {
  local config_file=$1
  local key=$2
  local value=$3
  local cce=$4
  local format=$5

  # Check sanity of the input
  if [ $# -lt "3" ]
  then
        echo "Usage: replace_or_append 'config_file_location' 'key_to_search' 'new_value'"
        echo
        echo "If symlinks need to be taken into account, add yes/no to the last argument"
        echo "to allow to 'follow_symlinks'."
        echo "Aborting."
        exit 1
  fi

  # Test if the config_file is a symbolic link. If so, use --follow-symlinks with sed.
  # Otherwise, regular sed command will do.
  if test -L $config_file; then
    sed_command="sed -i --follow-symlinks"
  else
    sed_command="sed -i"
  fi

  # Test that the cce arg is not empty or does not equal $CCENUM.
  # If $CCENUM exists, it means that there is no CCE assigned.
  if ! [ "x$cce" = x ] && [ "$cce" != '$CCENUM' ]; then
    cce="CCE-${cce}"
  else
    cce="CCE"
  fi

  # Strip any search characters in the key arg so that the key can be replaced without
  # adding any search characters to the config file.
  stripped_key=$(sed "s/[\^=\$,;+]*//g" <<< $key)

  # If there is no print format specified in the last arg, use the default format.
  if ! [ "x$format" = x ] ; then
    printf -v formatted_output "$format" $stripped_key $value
  else
    formatted_output="$stripped_key = $value"
  fi

  # If the key exists, change it. Otherwise, add it to the config_file.
  if `grep -qi $key $config_file` ; then
    $sed_command "s/$key.*/$formatted_output/g" $config_file
  else
    # \n is precaution for case where file ends without trailing newline
    echo -e "\n# Per $cce: Set $formatted_output in $config_file" >> $config_file
    echo -e "$formatted_output" >> $config_file
  fi

}

replace_or_append '/etc/systcl.conf' '^net.ipv4.conf.default.accept_source_route' '$sysctl_net_ipv4_conf_default_accept_source_route_value' 'CCE-80162-1'

Configure Kernel Parameter for Accepting ICMP Redirects By Default   [ref]rule

To set the runtime status of the net.ipv4.conf.default.accept_redirects kernel parameter, run the following command:

$ sudo sysctl -w net.ipv4.conf.default.accept_redirects=0
If this is not the system's default value, add the following line to /etc/sysctl.conf:
net.ipv4.conf.default.accept_redirects = 0

Rationale:

ICMP redirect messages are used by routers to inform hosts that a more direct route exists for a particular destination. These messages modify the host's route table and are unauthenticated. An illicit ICMP redirect message could result in a man-in-the-middle attack.
This feature of the IPv4 protocol has few legitimate uses. It should be disabled unless absolutely required.

identifiers:  CCE-80163-9

references:  AC-4, CM-7, SC-5, SC-7, 1551, 4.2.2, SRG-OS-000480-GPOS-00227, RHEL-07-040640, 5.10.1.1, 3.1.20

Remediation Shell script:   (show)

Complexity:low
Disruption:medium
Reboot:true
Strategy:disable

sysctl_net_ipv4_conf_default_accept_redirects_value="0"

#
# Set runtime for net.ipv4.conf.default.accept_redirects
#
/sbin/sysctl -q -n -w net.ipv4.conf.default.accept_redirects=$sysctl_net_ipv4_conf_default_accept_redirects_value

#
# If net.ipv4.conf.default.accept_redirects present in /etc/sysctl.conf, change value to appropriate value
#	else, add "net.ipv4.conf.default.accept_redirects = value" to /etc/sysctl.conf
#

function replace_or_append {
  local config_file=$1
  local key=$2
  local value=$3
  local cce=$4
  local format=$5

  # Check sanity of the input
  if [ $# -lt "3" ]
  then
        echo "Usage: replace_or_append 'config_file_location' 'key_to_search' 'new_value'"
        echo
        echo "If symlinks need to be taken into account, add yes/no to the last argument"
        echo "to allow to 'follow_symlinks'."
        echo "Aborting."
        exit 1
  fi

  # Test if the config_file is a symbolic link. If so, use --follow-symlinks with sed.
  # Otherwise, regular sed command will do.
  if test -L $config_file; then
    sed_command="sed -i --follow-symlinks"
  else
    sed_command="sed -i"
  fi

  # Test that the cce arg is not empty or does not equal $CCENUM.
  # If $CCENUM exists, it means that there is no CCE assigned.
  if ! [ "x$cce" = x ] && [ "$cce" != '$CCENUM' ]; then
    cce="CCE-${cce}"
  else
    cce="CCE"
  fi

  # Strip any search characters in the key arg so that the key can be replaced without
  # adding any search characters to the config file.
  stripped_key=$(sed "s/[\^=\$,;+]*//g" <<< $key)

  # If there is no print format specified in the last arg, use the default format.
  if ! [ "x$format" = x ] ; then
    printf -v formatted_output "$format" $stripped_key $value
  else
    formatted_output="$stripped_key = $value"
  fi

  # If the key exists, change it. Otherwise, add it to the config_file.
  if `grep -qi $key $config_file` ; then
    $sed_command "s/$key.*/$formatted_output/g" $config_file
  else
    # \n is precaution for case where file ends without trailing newline
    echo -e "\n# Per $cce: Set $formatted_output in $config_file" >> $config_file
    echo -e "$formatted_output" >> $config_file
  fi

}

replace_or_append '/etc/systcl.conf' '^net.ipv4.conf.default.accept_redirects' '$sysctl_net_ipv4_conf_default_accept_redirects_value' 'CCE-80163-9'

Configure Kernel Parameter to Ignore ICMP Broadcast Echo Requests   [ref]rule

To set the runtime status of the net.ipv4.icmp_echo_ignore_broadcasts kernel parameter, run the following command:

$ sudo sysctl -w net.ipv4.icmp_echo_ignore_broadcasts=1
If this is not the system's default value, add the following line to /etc/sysctl.conf:
net.ipv4.icmp_echo_ignore_broadcasts = 1

Rationale:

Responding to broadcast (ICMP) echoes facilitates network mapping and provides a vector for amplification attacks.
Ignoring ICMP echo requests (pings) sent to broadcast or multicast addresses makes the system slightly more difficult to enumerate on the network.

identifiers:  CCE-80165-4

references:  AC-4, CM-7, SC-5, 366, SRG-OS-000480-GPOS-00227, RHEL-07-040630, 4.2.5, 5.10.1.1, 3.1.20

Remediation Shell script:   (show)

Complexity:low
Disruption:medium
Reboot:true
Strategy:disable

sysctl_net_ipv4_icmp_echo_ignore_broadcasts_value="1"

#
# Set runtime for net.ipv4.icmp_echo_ignore_broadcasts
#
/sbin/sysctl -q -n -w net.ipv4.icmp_echo_ignore_broadcasts=$sysctl_net_ipv4_icmp_echo_ignore_broadcasts_value

#
# If net.ipv4.icmp_echo_ignore_broadcasts present in /etc/sysctl.conf, change value to appropriate value
#	else, add "net.ipv4.icmp_echo_ignore_broadcasts = value" to /etc/sysctl.conf
#

function replace_or_append {
  local config_file=$1
  local key=$2
  local value=$3
  local cce=$4
  local format=$5

  # Check sanity of the input
  if [ $# -lt "3" ]
  then
        echo "Usage: replace_or_append 'config_file_location' 'key_to_search' 'new_value'"
        echo
        echo "If symlinks need to be taken into account, add yes/no to the last argument"
        echo "to allow to 'follow_symlinks'."
        echo "Aborting."
        exit 1
  fi

  # Test if the config_file is a symbolic link. If so, use --follow-symlinks with sed.
  # Otherwise, regular sed command will do.
  if test -L $config_file; then
    sed_command="sed -i --follow-symlinks"
  else
    sed_command="sed -i"
  fi

  # Test that the cce arg is not empty or does not equal $CCENUM.
  # If $CCENUM exists, it means that there is no CCE assigned.
  if ! [ "x$cce" = x ] && [ "$cce" != '$CCENUM' ]; then
    cce="CCE-${cce}"
  else
    cce="CCE"
  fi

  # Strip any search characters in the key arg so that the key can be replaced without
  # adding any search characters to the config file.
  stripped_key=$(sed "s/[\^=\$,;+]*//g" <<< $key)

  # If there is no print format specified in the last arg, use the default format.
  if ! [ "x$format" = x ] ; then
    printf -v formatted_output "$format" $stripped_key $value
  else
    formatted_output="$stripped_key = $value"
  fi

  # If the key exists, change it. Otherwise, add it to the config_file.
  if `grep -qi $key $config_file` ; then
    $sed_command "s/$key.*/$formatted_output/g" $config_file
  else
    # \n is precaution for case where file ends without trailing newline
    echo -e "\n# Per $cce: Set $formatted_output in $config_file" >> $config_file
    echo -e "$formatted_output" >> $config_file
  fi

}

replace_or_append '/etc/systcl.conf' '^net.ipv4.icmp_echo_ignore_broadcasts' '$sysctl_net_ipv4_icmp_echo_ignore_broadcasts_value' 'CCE-80165-4'

Configure Kernel Parameter to Use TCP Syncookies   [ref]rule

To set the runtime status of the net.ipv4.tcp_syncookies kernel parameter, run the following command:

$ sudo sysctl -w net.ipv4.tcp_syncookies=1
If this is not the system's default value, add the following line to /etc/sysctl.conf:
net.ipv4.tcp_syncookies = 1

Rationale:

A TCP SYN flood attack can cause a denial of service by filling a system's TCP connection table with connections in the SYN_RCVD state. Syncookies can be used to track a connection when a subsequent ACK is received, verifying the initiator is attempting a valid connection and is not a flood source. This feature is activated when a flood condition is detected, and enables the system to continue servicing valid connection requests.

identifiers:  CCE-27495-1

references:  AC-4, SC-5(1)(2), SC-5(2), SC-5(3), 366, SRG-OS-000480-GPOS-00227, 4.2.8, 5.10.1.1, 3.1.20

Remediation Shell script:   (show)

Complexity:low
Disruption:medium
Reboot:true
Strategy:disable

sysctl_net_ipv4_tcp_syncookies_value="1"

#
# Set runtime for net.ipv4.tcp_syncookies
#
/sbin/sysctl -q -n -w net.ipv4.tcp_syncookies=$sysctl_net_ipv4_tcp_syncookies_value

#
# If net.ipv4.tcp_syncookies present in /etc/sysctl.conf, change value to appropriate value
#	else, add "net.ipv4.tcp_syncookies = value" to /etc/sysctl.conf
#

function replace_or_append {
  local config_file=$1
  local key=$2
  local value=$3
  local cce=$4
  local format=$5

  # Check sanity of the input
  if [ $# -lt "3" ]
  then
        echo "Usage: replace_or_append 'config_file_location' 'key_to_search' 'new_value'"
        echo
        echo "If symlinks need to be taken into account, add yes/no to the last argument"
        echo "to allow to 'follow_symlinks'."
        echo "Aborting."
        exit 1
  fi

  # Test if the config_file is a symbolic link. If so, use --follow-symlinks with sed.
  # Otherwise, regular sed command will do.
  if test -L $config_file; then
    sed_command="sed -i --follow-symlinks"
  else
    sed_command="sed -i"
  fi

  # Test that the cce arg is not empty or does not equal $CCENUM.
  # If $CCENUM exists, it means that there is no CCE assigned.
  if ! [ "x$cce" = x ] && [ "$cce" != '$CCENUM' ]; then
    cce="CCE-${cce}"
  else
    cce="CCE"
  fi

  # Strip any search characters in the key arg so that the key can be replaced without
  # adding any search characters to the config file.
  stripped_key=$(sed "s/[\^=\$,;+]*//g" <<< $key)

  # If there is no print format specified in the last arg, use the default format.
  if ! [ "x$format" = x ] ; then
    printf -v formatted_output "$format" $stripped_key $value
  else
    formatted_output="$stripped_key = $value"
  fi

  # If the key exists, change it. Otherwise, add it to the config_file.
  if `grep -qi $key $config_file` ; then
    $sed_command "s/$key.*/$formatted_output/g" $config_file
  else
    # \n is precaution for case where file ends without trailing newline
    echo -e "\n# Per $cce: Set $formatted_output in $config_file" >> $config_file
    echo -e "$formatted_output" >> $config_file
  fi

}

replace_or_append '/etc/systcl.conf' '^net.ipv4.tcp_syncookies' '$sysctl_net_ipv4_tcp_syncookies_value' 'CCE-27495-1'

Wireless Networking   [ref]group

Wireless networking, such as 802.11 (WiFi) and Bluetooth, can present a security risk to sensitive or classified systems and networks. Wireless networking hardware is much more likely to be included in laptop or portable systems than in desktops or servers.

Removal of hardware provides the greatest assurance that the wireless capability remains disabled. Acquisition policies often include provisions to prevent the purchase of equipment that will be used in sensitive spaces and includes wireless capabilities. If it is impractical to remove the wireless hardware, and policy permits the device to enter sensitive spaces as long as wireless is disabled, efforts should instead focus on disabling wireless capability via software.

contains 4 rules

Disable Wireless Through Software Configuration   [ref]group

If it is impossible to remove the wireless hardware from the device in question, disable as much of it as possible through software. The following methods can disable software support for wireless networking, but note that these methods do not prevent malicious software or careless users from re-activating the devices.

contains 4 rules

Disable WiFi or Bluetooth in BIOS   [ref]rule

Some machines that include built-in wireless support offer the ability to disable the device through the BIOS. This is hardware-specific; consult your hardware manual or explore the BIOS setup during boot.

Rationale:

Disabling wireless support in the BIOS prevents easy activation of the wireless interface, generally requiring administrators to reboot the system first.

identifiers:  CCE-27397-9

references:  AC-17(8), AC-18(a), AC-18(d), AC-18(3), CM-7, 85

Deactivate Wireless Network Interfaces   [ref]rule

Deactivating wireless network interfaces should prevent normal usage of the wireless capability.

First, identify the interfaces available with the command:

$ ifconfig -a
Additionally, the following command may be used to determine whether wireless support is included for a particular interface, though this may not always be a clear indicator:
$ iwconfig
After identifying any wireless interfaces (which may have names like wlan0, ath0, wifi0, em1 or eth0), deactivate the interface with the command:
$ sudo ifdown interface
These changes will only last until the next reboot. To disable the interface for future boots, remove the appropriate interface file from /etc/sysconfig/network-scripts:
$ sudo rm /etc/sysconfig/network-scripts/ifcfg-interface

Rationale:

Wireless networking allows attackers within physical proximity to launch network-based attacks against systems, including those against local LAN protocols which were not designed with security in mind.

identifiers:  CCE-27358-1

references:  AC-17(8), AC-18(a), AC-18(d), AC-18(3), CM-7, 85, 4.3.1, 3.1.16

Disable Bluetooth Service   [ref]rule

The bluetooth service can be disabled with the following command:

$ sudo systemctl disable bluetooth.service
$ sudo service bluetooth stop

Rationale:

Disabling the bluetooth service prevents the system from attempting connections to Bluetooth devices, which entails some security risk. Nevertheless, variation in this risk decision may be expected due to the utility of Bluetooth connectivity and its limited range.

identifiers:  CCE-27328-4

references:  AC-17(8), AC-18(a), AC-18(d), AC-18(3), CM-7, 85, 1551, 3.1.16

Remediation Shell script:   (show)

Complexity:low
Disruption:low
Strategy:disable
grep -qi disable /etc/xinetd.d/bluetooth && \
	sed -i 's/disable.*/disable	= yes/gI' /etc/xinetd.d/bluetooth
#
# Disable bluetooth.service for all systemd targets
#
systemctl disable bluetooth.service

#
# Stop bluetooth.service if currently running
#
systemctl stop bluetooth.service

Disable Bluetooth Kernel Modules   [ref]rule

The kernel's module loading system can be configured to prevent loading of the Bluetooth module. Add the following to the appropriate /etc/modprobe.d configuration file to prevent the loading of the Bluetooth module:

install bluetooth /bin/true

Rationale:

If Bluetooth functionality must be disabled, preventing the kernel from loading the kernel module provides an additional safeguard against its activation.

identifiers:  CCE-27327-6

references:  AC-17(8), AC-18(a), AC-18(d), AC-18(3), CM-7, 85, 1551, 5.13.1.3, 3.1.16

Remediation Shell script:   (show)

Complexity:low
Disruption:medium
Reboot:true
Strategy:disable
if grep --silent "^install bluetooth" /etc/modprobe.d/bluetooth.conf ; then
        sed -i 's/^install bluetooth.*/install bluetooth /bin/true/g' /etc/modprobe.d/bluetooth.conf
else
        echo -e "\n# Disable per security requirements" >> /etc/modprobe.d/bluetooth.conf
        echo "install bluetooth /bin/true" >> /etc/modprobe.d/bluetooth.conf
fi
Remediation Ansible snippet:   (show)

Complexity:low
Disruption:medium
Reboot:true
Strategy:disable
- name: Ensure kernel module 'bluetooth' is disabled
  lineinfile:
    create=yes
    dest="/etc/modprobe.d/{{item}}.conf"
    regexp="{{item}}"
    line="install {{item}} /bin/true"
  with_items:
    - bluetooth

IPv6   [ref]group

The system includes support for Internet Protocol version 6. A major and often-mentioned improvement over IPv4 is its enormous increase in the number of available addresses. Another important feature is its support for automatic configuration of many network settings.

contains 1 rule

Configure IPv6 Settings if Necessary   [ref]group

A major feature of IPv6 is the extent to which systems implementing it can automatically configure their networking devices using information from the network. From a security perspective, manually configuring important configuration information is preferable to accepting it from the network in an unauthenticated fashion.

contains 1 rule

Disable Automatic Configuration   [ref]group

Disable the system's acceptance of router advertisements and redirects by adding or correcting the following line in /etc/sysconfig/network (note that this does not disable sending router solicitations):

IPV6_AUTOCONF=no

contains 1 rule

Configure Kernel Parameter for Accepting Source-Routed Packets for All Interfaces   [ref]rule

To set the runtime status of the net.ipv6.conf.all.accept_source_route kernel parameter, run the following command:

$ sudo sysctl -w net.ipv6.conf.all.accept_source_route=0
If this is not the system's default value, add the following line to /etc/sysctl.conf:
net.ipv6.conf.all.accept_source_route = 0

Rationale:

Source-routed packets allow the source of the packet to suggest routers forward the packet along a different path than configured on the router, which can be used to bypass network security measures. This requirement applies only to the forwarding of source-routerd traffic, such as when IPv6 forwarding is enabled and the system is functioning as a router.

Accepting source-routed packets in the IPv6 protocol has few legitimate uses. It should be disabled unless it is absolutely required.

identifiers:  CCE-80179-5

references:  AC-4, 366, SRG-OS-000480-GPOS-00227, RHEL-07-040830, 3.1.20

Remediation Shell script:   (show)

Complexity:low
Disruption:medium
Reboot:true
Strategy:disable

sysctl_net_ipv6_conf_all_accept_source_route_value="0"

#
# Set runtime for net.ipv6.conf.all.accept_source_route
#
/sbin/sysctl -q -n -w net.ipv6.conf.all.accept_source_route=$sysctl_net_ipv6_conf_all_accept_source_route_value

#
# If net.ipv6.conf.all.accept_source_route present in /etc/sysctl.conf, change value to appropriate value
#	else, add "net.ipv6.conf.all.accept_source_route = value" to /etc/sysctl.conf
#

function replace_or_append {
  local config_file=$1
  local key=$2
  local value=$3
  local cce=$4
  local format=$5

  # Check sanity of the input
  if [ $# -lt "3" ]
  then
        echo "Usage: replace_or_append 'config_file_location' 'key_to_search' 'new_value'"
        echo
        echo "If symlinks need to be taken into account, add yes/no to the last argument"
        echo "to allow to 'follow_symlinks'."
        echo "Aborting."
        exit 1
  fi

  # Test if the config_file is a symbolic link. If so, use --follow-symlinks with sed.
  # Otherwise, regular sed command will do.
  if test -L $config_file; then
    sed_command="sed -i --follow-symlinks"
  else
    sed_command="sed -i"
  fi

  # Test that the cce arg is not empty or does not equal $CCENUM.
  # If $CCENUM exists, it means that there is no CCE assigned.
  if ! [ "x$cce" = x ] && [ "$cce" != '$CCENUM' ]; then
    cce="CCE-${cce}"
  else
    cce="CCE"
  fi

  # Strip any search characters in the key arg so that the key can be replaced without
  # adding any search characters to the config file.
  stripped_key=$(sed "s/[\^=\$,;+]*//g" <<< $key)

  # If there is no print format specified in the last arg, use the default format.
  if ! [ "x$format" = x ] ; then
    printf -v formatted_output "$format" $stripped_key $value
  else
    formatted_output="$stripped_key = $value"
  fi

  # If the key exists, change it. Otherwise, add it to the config_file.
  if `grep -qi $key $config_file` ; then
    $sed_command "s/$key.*/$formatted_output/g" $config_file
  else
    # \n is precaution for case where file ends without trailing newline
    echo -e "\n# Per $cce: Set $formatted_output in $config_file" >> $config_file
    echo -e "$formatted_output" >> $config_file
  fi

}

replace_or_append '/etc/systcl.conf' '^net.ipv6.conf.all.accept_source_route' '$sysctl_net_ipv6_conf_all_accept_source_route_value' 'CCE-80179-5'

firewalld   [ref]group

The dynamic firewall daemon firewalld provides a dynamically managed firewall with support for network “zones” to assign a level of trust to a network and its associated connections and interfaces. It has support for IPv4 and IPv6 firewall settings. It supports Ethernet bridges and has a separation of runtime and permanent configuration options. It also has an interface for services or applications to add firewall rules directly.
A graphical configuration tool, firewall-config, is used to configure firewalld, which in turn uses iptables tool to communicate with Netfilter in the kernel which implements packet filtering.
The firewall service provided by firewalld is dynamic rather than static because changes to the configuration can be made at anytime and are immediately implemented. There is no need to save or apply the changes. No unintended disruption of existing network connections occurs as no part of the firewall has to be reloaded.

contains 2 rules

Inspect and Activate Default firewalld Rules   [ref]group

Firewalls can be used to separate networks into different zones based on the level of trust the user has decided to place on the devices and traffic within that network. NetworkManager informs firewalld to which zone an interface belongs. An interface's assigned zone can be changed by NetworkManager or via the firewall-config tool.
The zone settings in /etc/firewalld/ are a range of preset settings which can be quickly applied to a network interface. These are the zones provided by firewalld sorted according to the default trust level of the zones from untrusted to trusted:

  • drop

    Any incoming network packets are dropped, there is no reply. Only outgoing network connections are possible.

  • block

    Any incoming network connections are rejected with an icmp-host-prohibited message for IPv4 and icmp6-adm-prohibited for IPv6. Only network connections initiated from within the system are possible.

  • public

    For use in public areas. You do not trust the other computers on the network to not harm your computer. Only selected incoming connections are accepted.

  • external

    For use on external networks with masquerading enabled especially for routers. You do not trust the other computers on the network to not harm your computer. Only selected incoming connections are accepted.

  • dmz

    For computers in your demilitarized zone that are publicly-accessible with limited access to your internal network. Only selected incoming connections are accepted.

  • work

    For use in work areas. You mostly trust the other computers on networks to not harm your computer. Only selected incoming connections are accepted.

  • home

    For use in home areas. You mostly trust the other computers on networks to not harm your computer. Only selected incoming connections are accepted.

  • internal

    For use on internal networks. You mostly trust the other computers on the networks to not harm your computer. Only selected incoming connections are accepted.

  • trusted

    All network connections are accepted.


It is possible to designate one of these zones to be the default zone. When interface connections are added to NetworkManager, they are assigned to the default zone. On installation, the default zone in firewalld is set to be the public zone.
To find out all the settings of a zone, for example the public zone, enter the following command as root:
# firewall-cmd --zone=public --list-all
Example output of this command might look like the following:
# firewall-cmd --zone=public --list-all
public
  interfaces:
  services: mdns dhcpv6-client ssh
  ports:
  forward-ports:
  icmp-blocks: source-quench
To view the network zones currently active, enter the following command as root:
# firewall-cmd --get-service
The following listing displays the result of this command on common Red Hat Enterprise Linux 7 Server system:
# firewall-cmd --get-service
amanda-client bacula bacula-client dhcp dhcpv6 dhcpv6-client dns ftp
high-availability http https imaps ipp ipp-client ipsec kerberos kpasswd
ldap ldaps libvirt libvirt-tls mdns mountd ms-wbt mysql nfs ntp openvpn
pmcd pmproxy pmwebapi pmwebapis pop3s postgresql proxy-dhcp radius rpc-bind
samba samba-client smtp ssh telnet tftp tftp-client transmission-client
vnc-server wbem-https
Finally to view the network zones that will be active after the next firewalld service reload, enter the following command as root:
# firewall-cmd --get-service --permanent

contains 1 rule

Verify firewalld Enabled   [ref]rule

The firewalld service can be enabled with the following command:

$ sudo systemctl enable firewalld.service

Rationale:

Access control methods provide the ability to enhance system security posture by restricting services and known good IP addresses and address ranges. This prevents connections from unknown hosts and protocols.

identifiers:  CCE-27361-5

references:  CM-6(b), 366, 4.7, SRG-OS-000480-GPOS-00227, RHEL-07-040520, 3.1.3, 3.4.7

Remediation Shell script:   (show)

Complexity:low
Disruption:low
Strategy:enable

function service_command {

# Load function arguments into local variables
local service_state=$1
local service=$2
local xinetd=$(echo $3 | cut -d'=' -f2)

# Check sanity of the input
if [ $# -lt "2" ]
then
  echo "Usage: service_command 'enable/disable' 'service_name.service'"
  echo
  echo "To enable or disable xinetd services add \'xinetd=service_name\'"
  echo "as the last argument"
  echo "Aborting."
  exit 1
fi

# If systemctl is installed, use systemctl command; otherwise, use the service/chkconfig commands
if [ -f "/usr/bin/systemctl" ] ; then
  service_util="/usr/bin/systemctl"
else
  service_util="/sbin/service"
  chkconfig_util="/sbin/chkconfig"
fi

# If disable is not specified in arg1, set variables to enable services.
# Otherwise, variables are to be set to disable services.
if [ "$service_state" != 'disable' ] ; then
  service_state="enable"
  service_operation="start"
  chkconfig_state="on"
else
  service_state="disable"
  service_operation="stop"
  chkconfig_state="off"
fi

# If chkconfig_util is not empty, use chkconfig/service commands.
if ! [ "x$chkconfig_util" = x ] ; then
  $service_util $service $service_operation
  $chkconfig_util --level 0123456 $service $chkconfig_state
else
  $service_util $service_operation $service
  $service_util $service_state $service
fi

# Test if local variable xinetd is empty using non-bashism.
# If empty, then xinetd is not being used.
if ! [ "x$xinetd" = x ] ; then
  grep -qi disable /etc/xinetd.d/$xinetd && \

  if ! [ "$service_operation" != 'disable' ] ; then
    sed -i "s/disable.*/disable         = no/gI" /etc/xinetd.d/$xinetd
  else
    sed -i "s/disable.*/disable         = yes/gI" /etc/xinetd.d/$xinetd
  fi
fi

}

service_command enable firewalld
Remediation Ansible snippet:   (show)

Complexity:low
Disruption:low
Strategy:enable
- name: Enable service firewalld
  service:
    name="{{item}}"
    enabled="yes"
    state="started"
  with_items:
    - firewalld

Strengthen the Default Ruleset   [ref]group

The default rules can be strengthened. The system scripts that activate the firewall rules expect them to be defined in configuration files under the /etc/firewalld/services and /etc/firewalld/zones directories.

The following recommendations describe how to strengthen the default ruleset configuration file. An alternative to editing this configuration file is to create a shell script that makes calls to the firewall-cmd program to load in rules under the /etc/firewalld/services and /etc/firewalld/zones directories.

Instructions apply to both unless otherwise noted. Language and address conventions for regular firewalld rules are used throughout this section.

warning  The program firewall-config allows additional services to penetrate the default firewall rules and automatically adjusts the firewalld ruleset(s).
contains 1 rule

Set Default firewalld Zone for Incoming Packets   [ref]rule

To set the default zone to drop for the built-in default zone which processes incoming IPv4 and IPv6 packets, modify the following line in /etc/firewalld/firewalld.conf to be:

DefaultZone=drop

Rationale:

In firewalld the default zone is applied only after all the applicable rules in the table are examined for a match. Setting the default zone to drop implements proper design for a firewall, i.e. any packets which are not explicitly permitted should not be accepted.

identifiers:  CCE-27349-0

references:  CM-6(b), CM-7, 366, SRG-OS-000480-GPOS-00227, 5.10.1, 3.1.3, 3.4.7, 3.13.6

Remediation Shell script:   (show)

Complexity:low
Disruption:low
Strategy:disable
grep -q ^DefaultZone= /etc/firewalld/firewalld.conf && \
  sed -i "s/DefaultZone=.*/DefaultZone=drop/g" /etc/firewalld/firewalld.conf
if ! [ $? -eq 0 ]; then
    echo "DefaultZone=drop" >> /etc/firewalld/firewalld.conf
fi

IPSec Support   [ref]group

Support for Internet Protocol Security (IPsec) is provided in Red Hat Enterprise Linux 7 with Libreswan.

contains 2 rules

Install libreswan Package   [ref]rule

The Libreswan package provides an implementation of IPsec and IKE, which permits the creation of secure tunnels over untrusted networks. The libreswan package can be installed with the following command:

$ sudo yum install libreswan

Rationale:

Providing the ability for remote users or systems to initiate a secure VPN connection protects information when it is transmitted over a wide area network.

identifiers:  CCE-80170-4

references:  AC-17, MA-4, SC-9, 1130, 1131, Req-4.1

Remediation Shell script:   (show)

Complexity:low
Disruption:low
Strategy:enable

function package_command {

# Load function arguments into local variables
local package_operation=$1
local package=$2

# Check sanity of the input
if [ $# -ne "2" ]
then
  echo "Usage: package_command 'install/uninstall' 'rpm_package_name"
  echo "Aborting."
  exit 1
fi

# If dnf is installed, use dnf; otherwise, use yum
if [ -f "/usr/bin/dnf" ] ; then
  install_util="/usr/bin/dnf"
else
  install_util="/usr/bin/yum"
fi

if [ "$package_operation" != 'remove' ] ; then
  # If the rpm is not installed, install the rpm
  if ! /bin/rpm -q --quiet $package; then
    $install_util -y $package_operation $package
  fi
else
  # If the rpm is installed, uninstall the rpm
  if /bin/rpm -q --quiet $package; then
    $install_util -y $package_operation $package
  fi
fi

}

package_command install libreswan
Remediation Ansible snippet:   (show)

Complexity:low
Disruption:low
Strategy:enable
- name: Ensure libreswan is installed
  package:
    name="{{item}}"
    state=present
  with_items:
    - libreswan
Remediation Puppet snippet:   (show)

Complexity:low
Disruption:low
Strategy:enable
include install_libreswan

class install_libreswan {
  package { 'libreswan':
    ensure => 'installed',
  }
}
Remediation script:   (show)

Complexity:low
Disruption:low
Strategy:enable

package -add=libreswan

Verify Any Configured IPSec Tunnel Connections   [ref]rule

Libreswan provides an implementation of IPsec and IKE, which permits the creation of secure tunnels over untrusted networks. As such, IPsec can be used to circumvent certain network requirements such as filtering. Verify that if any IPsec connection (conn) configured in /etc/ipsec.conf and /etc/ipsec.d exists is an approved organizational connection.

Rationale:

IP tunneling mechanisms can be used to bypass network filtering.

identifiers:  CCE-80171-2

references:  AC-4, 336, SRG-OS-000480-GPOS-00227, RHEL-07-040820

Disable Client Dynamic DNS Updates   [ref]rule

Dynamic DNS allows clients to dynamically update their own DNS records. The updates are transmitted by unencrypted means which can reveal information to a potential malicious user. If the system does not require Dynamic DNS, remove all DHCP_HOSTNAME references from the /etc/sysconfig/network-scripts/ifcfg-interface scripts. If dhclient is used, remove all send host-name hostname references from the /etc/dhclient.conf configuration file and/or any reference from the /etc/dhcp directory.

Rationale:

Dynamic DNS updates transmit unencrypted information about a system including its name and address and should not be used unless needed.

identifiers:  CCE-80357-7

references:  CM-6(b), 366, SRG-OS-000480-GPOS-00227

Ensure System is Not Acting as a Network Sniffer   [ref]rule

The system should not be acting as a network sniffer, which can capture all traffic on the network to which it is connected. Run the following to determine if any interface is running in promiscuous mode:

$ ip link | grep PROMISC

Rationale:

Network interfaces in promiscuous mode allow for the capture of all network traffic visible to the system. If unauthorized individuals can access these applications, it may allow them to collect information such as logon IDs, passwords, and key exchanges between systems.

If the system is being used to perform a network troubleshooting function, the use of these tools must be documented with the Information Systems Security Manager (ISSM) and restricted to only authorized personnel.

Configure Syslog   [ref]group

The syslog service has been the default Unix logging mechanism for many years. It has a number of downsides, including inconsistent log format, lack of authentication for received messages, and lack of authentication, encryption, or reliable transport for messages sent over a network. However, due to its long history, syslog is a de facto standard which is supported by almost all Unix applications.

In Red Hat Enterprise Linux 7, rsyslog has replaced ksyslogd as the syslog daemon of choice, and it includes some additional security features such as reliable, connection-oriented (i.e. TCP) transmission of logs, the option to log to database formats, and the encryption of log data en route to a central logging server. This section discusses how to configure rsyslog for best effect, and how to use tools provided with the system to maintain and monitor logs.

contains 3 rules

Ensure Proper Configuration of Log Files   [ref]group

The file /etc/rsyslog.conf controls where log message are written. These are controlled by lines called rules, which consist of a selector and an action. These rules are often customized depending on the role of the system, the requirements of the environment, and whatever may enable the administrator to most effectively make use of log data. The default rules in Red Hat Enterprise Linux 7 are:

*.info;mail.none;authpriv.none;cron.none                /var/log/messages
authpriv.*                                              /var/log/secure
mail.*                                                  -/var/log/maillog
cron.*                                                  /var/log/cron
*.emerg                                                 *
uucp,news.crit                                          /var/log/spooler
local7.*                                                /var/log/boot.log
See the man page rsyslog.conf(5) for more information. Note that the rsyslog daemon can be configured to use a timestamp format that some log processing programs may not understand. If this occurs, edit the file /etc/rsyslog.conf and add or edit the following line:
$ ActionFileDefaultTemplate RSYSLOG_TraditionalFileFormat

contains 1 rule

Ensure cron Is Logging To Rsyslog   [ref]rule

Cron logging must be implemented to spot intrusions or trace cron job status. If cron is not logging to rsyslog, it can be implemented by adding the following to the RULES section of /etc/rsyslog.conf:

cron.*                                                  /var/log/cron

Rationale:

Cron logging can be used to trace the successful or unsuccessful execution of cron jobs. It can also be used to spot intrusions into the use of the cron facility by unauthorized and malicious users.

identifiers:  CCE-80380-9

references:  AU-2(d), 366, SRG-OS-000480-GPOS-00227, RHEL-07-021100

Rsyslog Logs Sent To Remote Host   [ref]group

If system logs are to be useful in detecting malicious activities, it is necessary to send logs to a remote server. An intruder who has compromised the root account on a system may delete the log entries which indicate that the system was attacked before they are seen by an administrator.

However, it is recommended that logs be stored on the local host in addition to being sent to the loghost, especially if rsyslog has been configured to use the UDP protocol to send messages over a network. UDP does not guarantee reliable delivery, and moderately busy sites will lose log messages occasionally, especially in periods of high traffic which may be the result of an attack. In addition, remote rsyslog messages are not authenticated in any way by default, so it is easy for an attacker to introduce spurious messages to the central log server. Also, some problems cause loss of network connectivity, which will prevent the sending of messages to the central server. For all of these reasons, it is better to store log messages both centrally and on each host, so that they can be correlated if necessary.

contains 1 rule

Ensure Logs Sent To Remote Host   [ref]rule

To configure rsyslog to send logs to a remote log server, open /etc/rsyslog.conf and read and understand the last section of the file, which describes the multiple directives necessary to activate remote logging. Along with these other directives, the system can be configured to forward its logs to a particular log server by adding or correcting one of the following lines, substituting loghost.example.com appropriately. The choice of protocol depends on the environment of the system; although TCP and RELP provide more reliable message delivery, they may not be supported in all environments.
To use UDP for log message delivery:

*.* @loghost.example.com

To use TCP for log message delivery:
*.* @@loghost.example.com

To use RELP for log message delivery:
*.* :omrelp:loghost.example.com

Rationale:

A log server (loghost) receives syslog messages from one or more systems. This data can be used as an additional log source in the event a system is compromised and its local logs are suspect. Forwarding log messages to a remote loghost also provides system administrators with a centralized place to view the status of multiple hosts within the enterprise.

identifiers:  CCE-27343-3

references:  AU-3(2), AU-4(1), AU-9, 366, 1348, 136, 1851, 5.1.5, SRG-OS-000480-GPOS-00227, RHEL-07-031000

Configure rsyslogd to Accept Remote Messages If Acting as a Log Server   [ref]group

By default, rsyslog does not listen over the network for log messages. If needed, modules can be enabled to allow the rsyslog daemon to receive messages from other systems and for the system thus to act as a log server. If the system is not a log server, then lines concerning these modules should remain commented out.

contains 1 rule

Ensure rsyslog Does Not Accept Remote Messages Unless Acting As Log Server   [ref]rule

The rsyslog daemon should not accept remote messages unless the system acts as a log server. To ensure that it is not listening on the network, ensure the following lines are not found in /etc/rsyslog.conf:

$ModLoad imtcp
$InputTCPServerRun port
$ModLoad imudp
$UDPServerRun port
$ModLoad imrelp
$InputRELPServerRun port

Rationale:

Any process which receives messages from the network incurs some risk of receiving malicious messages. This risk can be eliminated for rsyslog by configuring it not to listen on the network.

identifiers:  CCE-80192-8

references:  AU-9(2), AC-4, CM-6(c), 318, 368, 1812, 1813, 1814, SRG-OS-000480-GPOS-00227, RHEL-07-031010

System Accounting with auditd   [ref]group

The audit service provides substantial capabilities for recording system activities. By default, the service audits about SELinux AVC denials and certain types of security-relevant events such as system logins, account modifications, and authentication events performed by programs such as sudo. Under its default configuration, auditd has modest disk space requirements, and should not noticeably impact system performance.

NOTE: The Linux Audit daemon auditd can be configured to use the augenrules program to read audit rules files (*.rules) located in /etc/audit/rules.d location and compile them to create the resulting form of the /etc/audit/audit.rules configuration file during the daemon startup (default configuration). Alternatively, the auditd daemon can use the auditctl utility to read audit rules from the /etc/audit/audit.rules configuration file during daemon startup, and load them into the kernel. The expected behavior is configured via the appropriate ExecStartPost directive setting in the /usr/lib/systemd/system/auditd.service configuration file. To instruct the auditd daemon to use the augenrules program to read audit rules (default configuration), use the following setting:

ExecStartPost=-/sbin/augenrules --load
in the /usr/lib/systemd/system/auditd.service configuration file. In order to instruct the auditd daemon to use the auditctl utility to read audit rules, use the following setting:
ExecStartPost=-/sbin/auditctl -R /etc/audit/audit.rules
in the /usr/lib/systemd/system/auditd.service configuration file. Refer to [Service] section of the /usr/lib/systemd/system/auditd.service configuration file for further details.

Government networks often have substantial auditing requirements and auditd can be configured to meet these requirements. Examining some example audit records demonstrates how the Linux audit system satisfies common requirements. The following example from Fedora Documentation available at https://access.redhat.com/documentation/en-US/Red_Hat_Enterprise_Linux/7/html/SELinux_Users_and_Administrators_Guide/sect-Security-Enhanced_Linux-Troubleshooting-Fixing_Problems.html#sect-Security-Enhanced_Linux-Fixing_Problems-Raw_Audit_Messages shows the substantial amount of information captured in a two typical "raw" audit messages, followed by a breakdown of the most important fields. In this example the message is SELinux-related and reports an AVC denial (and the associated system call) that occurred when the Apache HTTP Server attempted to access the /var/www/html/file1 file (labeled with the samba_share_t type):
type=AVC msg=audit(1226874073.147:96): avc:  denied  { getattr } for pid=2465 comm="httpd"
path="/var/www/html/file1" dev=dm-0 ino=284133 scontext=unconfined_u:system_r:httpd_t:s0
tcontext=unconfined_u:object_r:samba_share_t:s0 tclass=file

type=SYSCALL msg=audit(1226874073.147:96): arch=40000003 syscall=196 success=no exit=-13
a0=b98df198 a1=bfec85dc a2=54dff4 a3=2008171 items=0 ppid=2463 pid=2465 auid=502 uid=48
gid=48 euid=48 suid=48 fsuid=48 egid=48 sgid=48 fsgid=48 tty=(none) ses=6 comm="httpd"
exe="/usr/sbin/httpd" subj=unconfined_u:system_r:httpd_t:s0 key=(null)
  • msg=audit(1226874073.147:96)
    • The number in parentheses is the unformatted time stamp (Epoch time) for the event, which can be converted to standard time by using the date command.
  • { getattr }
    • The item in braces indicates the permission that was denied. getattr indicates the source process was trying to read the target file's status information. This occurs before reading files. This action is denied due to the file being accessed having the wrong label. Commonly seen permissions include getattr, read, and write.
  • comm="httpd"
    • The executable that launched the process. The full path of the executable is found in the exe= section of the system call (SYSCALL) message, which in this case, is exe="/usr/sbin/httpd".
  • path="/var/www/html/file1"
    • The path to the object (target) the process attempted to access.
  • scontext="unconfined_u:system_r:httpd_t:s0"
    • The SELinux context of the process that attempted the denied action. In this case, it is the SELinux context of the Apache HTTP Server, which is running in the httpd_t domain.
  • tcontext="unconfined_u:object_r:samba_share_t:s0"
    • The SELinux context of the object (target) the process attempted to access. In this case, it is the SELinux context of file1. Note: the samba_share_t type is not accessible to processes running in the httpd_t domain.
  • From the system call (SYSCALL) message, two items are of interest:
    • success=no: indicates whether the denial (AVC) was enforced or not. success=no indicates the system call was not successful (SELinux denied access). success=yes indicates the system call was successful - this can be seen for permissive domains or unconfined domains, such as initrc_t and kernel_t.
    • exe="/usr/sbin/httpd": the full path to the executable that launched the process, which in this case, is exe="/usr/sbin/httpd".

contains 82 rules

Configure auditd Data Retention   [ref]group

The audit system writes data to /var/log/audit/audit.log. By default, auditd rotates 5 logs by size (6MB), retaining a maximum of 30MB of data in total, and refuses to write entries when the disk is too full. This minimizes the risk of audit data filling its partition and impacting other services. This also minimizes the risk of the audit daemon temporarily disabling the system if it cannot write audit log (which it can be configured to do). For a busy system or a system which is thoroughly auditing system activity, the default settings for data retention may be insufficient. The log file size needed will depend heavily on what types of events are being audited. First configure auditing to log all the events of interest. Then monitor the log size manually for awhile to determine what file size will allow you to keep the required data for the correct time period.

Using a dedicated partition for /var/log/audit prevents the auditd logs from disrupting system functionality if they fill, and, more importantly, prevents other activity in /var from filling the partition and stopping the audit trail. (The audit logs are size-limited and therefore unlikely to grow without bound unless configured to do so.) Some machines may have requirements that no actions occur which cannot be audited. If this is the case, then auditd can be configured to halt the machine if it runs out of space. Note: Since older logs are rotated, configuring auditd this way does not prevent older logs from being rotated away before they can be viewed. If your system is configured to halt when logging cannot be performed, make sure this can never happen under normal circumstances! Ensure that /var/log/audit is on its own partition, and that this partition is larger than the maximum amount of data auditd will retain normally.

references:  AU-11, 138

contains 8 rules

Configure auditd Number of Logs Retained   [ref]rule

Determine how many log files auditd should retain when it rotates logs. Edit the file /etc/audit/auditd.conf. Add or modify the following line, substituting NUMLOGS with the correct value of 5:

num_logs = NUMLOGS
Set the value to 5 for general-purpose systems. Note that values less than 2 result in no log rotation.

Rationale:

The total storage for audit log files must be large enough to retain log information over the period required. This is a function of the maximum log file size and the number of logs retained.

identifiers:  CCE-27348-2

references:  AU-1(b), AU-11, IR-5, Req-10.7, 5.4.1.1, 3.3.1

Remediation Shell script:   (show)

Complexity:low
Disruption:low
Strategy:disable

var_auditd_num_logs="5"

AUDITCONFIG=/etc/audit/auditd.conf

grep -q ^num_logs $AUDITCONFIG && \
  sed -i 's/^num_logs.*/num_logs = '"$var_auditd_num_logs"'/g' $AUDITCONFIG
if ! [ $? -eq 0 ]; then
  echo "num_logs = $var_auditd_num_logs" >> $AUDITCONFIG
fi

Configure auditd Max Log File Size   [ref]rule

Determine the amount of audit data (in megabytes) which should be retained in each log file. Edit the file /etc/audit/auditd.conf. Add or modify the following line, substituting the correct value of 6 for STOREMB:

max_log_file = STOREMB
Set the value to 6 (MB) or higher for general-purpose systems. Larger values, of course, support retention of even more audit data.

Rationale:

The total storage for audit log files must be large enough to retain log information over the period required. This is a function of the maximum log file size and the number of logs retained.

identifiers:  CCE-27319-3

references:  AU-1(b), AU-11, IR-5, Req-10.7, 5.2.1.1, 5.4.1.1

Remediation Shell script:   (show)

Complexity:low
Disruption:low
Strategy:disable

var_auditd_max_log_file="6"

AUDITCONFIG=/etc/audit/auditd.conf

grep -q ^max_log_file $AUDITCONFIG && \
  sed -i 's/^max_log_file.*/max_log_file = '"$var_auditd_max_log_file"'/g' $AUDITCONFIG
if ! [ $? -eq 0 ]; then
  echo "max_log_file = $var_auditd_max_log_file" >> $AUDITCONFIG
fi

Configure auditd max_log_file_action Upon Reaching Maximum Log Size   [ref]rule

The default action to take when the logs reach their maximum size is to rotate the log files, discarding the oldest one. To configure the action taken by auditd, add or correct the line in /etc/audit/auditd.conf:

max_log_file_action = ACTION
Possible values for ACTION are described in the auditd.conf man page. These include:
  • ignore
  • syslog
  • suspend
  • rotate
  • keep_logs
Set the ACTION to rotate to ensure log rotation occurs. This is the default. The setting is case-insensitive.

Rationale:

Automatically rotating logs (by setting this to rotate) minimizes the chances of the system unexpectedly running out of disk space by being overwhelmed with log data. However, for systems that must never discard log data, or which use external processes to transfer it and reclaim space, keep_logs can be employed.

identifiers:  CCE-27231-0

references:  AU-1(b), AU-4, AU-11, IR-5, Req-10.7, 5.2.1.3, 5.4.1.1

Remediation Shell script:   (show)

Complexity:low
Disruption:low
Strategy:disable

var_auditd_max_log_file_action="rotate"

AUDITCONFIG=/etc/audit/auditd.conf

grep -q ^max_log_file_action $AUDITCONFIG && \
  sed -i 's/^max_log_file_action.*/max_log_file_action = '"$var_auditd_max_log_file_action"'/g' $AUDITCONFIG
if ! [ $? -eq 0 ]; then
  echo "max_log_file_action = $var_auditd_max_log_file_action" >> $AUDITCONFIG
fi

Configure auditd space_left Action on Low Disk Space   [ref]rule

The auditd service can be configured to take an action when disk space starts to run low. Edit the file /etc/audit/auditd.conf. Modify the following line, substituting ACTION appropriately:

space_left_action = ACTION
Possible values for ACTION are described in the auditd.conf man page. These include:
  • ignore
  • syslog
  • email
  • exec
  • suspend
  • single
  • halt
Set this to email (instead of the default, which is suspend) as it is more likely to get prompt attention. Acceptable values also include suspend, single, and halt.

Rationale:

Notifying administrators of an impending disk space problem may allow them to take corrective action prior to any disruption.

identifiers:  CCE-27375-5

references:  AU-1(b), AU-4, AU-5(1), AU-5(b), IR-5, 1855, Req-10.7, 5.2.1.2, SRG-OS-000343-GPOS-00134, 030340, 5.4.1.1, 3.3.1

Remediation Shell script:   (show)

Complexity:low
Disruption:low
Strategy:disable

var_auditd_space_left_action="email"

grep -q ^space_left_action /etc/audit/auditd.conf && \
  sed -i "s/space_left_action.*/space_left_action = $var_auditd_space_left_action/g" /etc/audit/auditd.conf
if ! [ $? -eq 0 ]; then
    echo "space_left_action = $var_auditd_space_left_action" >> /etc/audit/auditd.conf
fi

Configure auditd admin_space_left Action on Low Disk Space   [ref]rule

The auditd service can be configured to take an action when disk space is running low but prior to running out of space completely. Edit the file /etc/audit/auditd.conf. Add or modify the following line, substituting ACTION appropriately:

admin_space_left_action = ACTION
Set this value to single to cause the system to switch to single user mode for corrective action. Acceptable values also include suspend and halt. For certain systems, the need for availability outweighs the need to log all actions, and a different setting should be determined. Details regarding all possible values for ACTION are described in the auditd.conf man page.

Rationale:

Administrators should be made aware of an inability to record audit records. If a separate partition or logical volume of adequate size is used, running low on space for audit records should never occur.

identifiers:  CCE-27370-6

references:  AU-1(b), AU-4, AU-5(b), IR-5, 140, 1343, Req-10.7, 5.2.1.2, 5.4.1.1, 3.3.1

Remediation Shell script:   (show)

Complexity:low
Disruption:low
Strategy:disable

var_auditd_admin_space_left_action="single"

grep -q ^admin_space_left_action /etc/audit/auditd.conf && \
  sed -i "s/admin_space_left_action.*/admin_space_left_action = $var_auditd_admin_space_left_action/g" /etc/audit/auditd.conf
if ! [ $? -eq 0 ]; then
    echo "admin_space_left_action = $var_auditd_admin_space_left_action" >> /etc/audit/auditd.conf
fi

Configure auditd mail_acct Action on Low Disk Space   [ref]rule

The auditd service can be configured to send email to a designated account in certain situations. Add or correct the following line in /etc/audit/auditd.conf to ensure that administrators are notified via email for those situations:

action_mail_acct = root

Rationale:

Email sent to the root account is typically aliased to the administrators of the system, who can take appropriate action.

Remediation Shell script:   (show)

Complexity:low
Disruption:low
Strategy:disable

var_auditd_action_mail_acct="root"

AUDITCONFIG=/etc/audit/auditd.conf

grep -q ^action_mail_acct $AUDITCONFIG && \
  sed -i 's/^action_mail_acct.*/action_mail_acct = '"$var_auditd_action_mail_acct"'/g' $AUDITCONFIG
if ! [ $? -eq 0 ]; then
  echo "action_mail_acct = $var_auditd_action_mail_acct" >> $AUDITCONFIG
fi

Configure auditd flush priority   [ref]rule

The auditd service can be configured to synchronously write audit event data to disk. Add or correct the following line in /etc/audit/auditd.conf to ensure that audit event data is fully synchronized with the log files on the disk:

flush = data

Rationale:

Audit data should be synchronously written to disk to ensure log integrity. These parameters assure that all audit event data is fully synchronized with the log files on the disk.

identifiers:  CCE-27331-8

references:  AU-9, AU-12(1), 1576, 3.3.1

Remediation Shell script:   (show)

Complexity:high
Disruption:medium
Strategy:restrict

var_auditd_flush="data"

AUDITCONFIG=/etc/audit/auditd.conf

# if flush is present, flush param edited to var_auditd_flush
# else flush param is defined by var_auditd_flush
#
# the freq param is only used value 'incremental' and will be
# commented out if flush != incremental
#
# if flush == incremental && freq param is not defined, it 
# will be defined as the package-default value of 20

grep -q ^flush $AUDITCONFIG && \
  sed -i 's/^flush.*/flush = '"$var_auditd_flush"'/g' $AUDITCONFIG
if ! [ $? -eq 0 ]; then
  echo "flush = $var_auditd_flush" >> $AUDITCONFIG
fi

if ! [ "$var_auditd_flush" == "incremental" ]; then
  sed -i 's/^freq/##freq/g' $AUDITCONFIG
elif [ "$var_auditd_flush" == "incremental" ]; then
  grep -q freq $AUDITCONFIG && \
    sed -i 's/^#\+freq/freq/g' $AUDITCONFIG
  if ! [ $? -eq 0 ]; then
    echo "freq = 20" >> $AUDITCONFIG
  fi
fi

Configure auditd to use audispd's syslog plugin   [ref]rule

To configure the auditd service to use the syslog plug-in of the audispd audit event multiplexor, set the active line in /etc/audisp/plugins.d/syslog.conf to yes. Restart the auditd service:

$ sudo service auditd restart

Rationale:

The auditd service does not include the ability to send audit records to a centralized server for management directly. It does, however, include a plug-in for audit event multiplexor (audispd) to pass audit records to the local syslog server

identifiers:  CCE-27341-7

references:  AU-1(b), AU-3(2), IR-5, 136, Req-10.5.3, 5.4.1.1, 3.3.1

Remediation Shell script:   (show)

Complexity:low
Disruption:low
Strategy:disable

grep -q ^active /etc/audisp/plugins.d/syslog.conf && \
  sed -i "s/active.*/active = yes/g" /etc/audisp/plugins.d/syslog.conf
if ! [ $? -eq 0 ]; then
    echo "active = yes" >> /etc/audisp/plugins.d/syslog.conf
fi

Configure auditd Rules for Comprehensive Auditing   [ref]group

The auditd program can perform comprehensive monitoring of system activity. This section describes recommended configuration settings for comprehensive auditing, but a full description of the auditing system's capabilities is beyond the scope of this guide. The mailing list linux-audit@redhat.com exists to facilitate community discussion of the auditing system.

The audit subsystem supports extensive collection of events, including:

  • Tracing of arbitrary system calls (identified by name or number) on entry or exit.
  • Filtering by PID, UID, call success, system call argument (with some limitations), etc.
  • Monitoring of specific files for modifications to the file's contents or metadata.

Auditing rules at startup are controlled by the file /etc/audit/audit.rules. Add rules to it to meet the auditing requirements for your organization. Each line in /etc/audit/audit.rules represents a series of arguments that can be passed to auditctl and can be individually tested during runtime. See documentation in /usr/share/doc/audit-VERSION and in the related man pages for more details.

If copying any example audit rulesets from /usr/share/doc/audit-VERSION, be sure to comment out the lines containing arch= which are not appropriate for your system's architecture. Then review and understand the following rules, ensuring rules are activated as needed for the appropriate architecture.

After reviewing all the rules, reading the following sections, and editing as needed, the new rules can be activated as follows:
$ sudo service auditd restart

contains 72 rules

Records Events that Modify Date and Time Information   [ref]group

Arbitrary changes to the system time can be used to obfuscate nefarious activities in log files, as well as to confuse network services that are highly dependent upon an accurate system time. All changes to the system time should be audited.

contains 5 rules

Record attempts to alter time through adjtimex   [ref]rule

If the auditd daemon is configured to use the augenrules program to read audit rules during daemon startup (the default), add the following line to a file with suffix .rules in the directory /etc/audit/rules.d:

-a always,exit -F arch=b32 -S adjtimex -F key=audit_time_rules
If the system is 64 bit then also add the following line:
-a always,exit -F arch=b64 -S adjtimex -F key=audit_time_rules
If the auditd daemon is configured to use the auditctl utility to read audit rules during daemon startup, add the following line to /etc/audit/audit.rules file:
-a always,exit -F arch=b32 -S adjtimex -F key=audit_time_rules
If the system is 64 bit then also add the following line:
-a always,exit -F arch=b64 -S adjtimex -F key=audit_time_rules
The -k option allows for the specification of a key in string form that can be used for better reporting capability through ausearch and aureport. Multiple system calls can be defined on the same line to save space if desired, but is not required. See an example of multiple combined syscalls:
-a always,exit -F arch=b64 -S adjtimex,settimeofday -F key=audit_time_rules

Rationale:

Arbitrary changes to the system time can be used to obfuscate nefarious activities in log files, as well as to confuse network services that are highly dependent upon an accurate system time (such as sshd). All changes to the system time should be audited.

identifiers:  CCE-27290-6

references:  AC-17(7), AU-1(b), AU-2(a), AU-2(c), AU-2(d), AU-12(a), AU-12(c), IR-5, 5.2.4, Req-10.4.2.b, 1487, 169, 5.4.1.1, 3.1.7

Remediation Shell script:   (show)

Complexity:low
Disruption:low
Strategy:disable

function fix_audit_syscall_rule {

# Load function arguments into local variables
local tool="$1"
local pattern="$2"
local group="$3"
local arch="$4"
local full_rule="$5"

# Check sanity of the input
if [ $# -ne "5" ]
then
        echo "Usage: fix_audit_syscall_rule 'tool' 'pattern' 'group' 'arch' 'full rule'"
        echo "Aborting."
        exit 1
fi

# Create a list of audit *.rules files that should be inspected for presence and correctness
# of a particular audit rule. The scheme is as follows:
# 
# -----------------------------------------------------------------------------------------
#  Tool used to load audit rules | Rule already defined  |  Audit rules file to inspect    |
# -----------------------------------------------------------------------------------------
#        auditctl                |     Doesn't matter    |  /etc/audit/audit.rules         |
# -----------------------------------------------------------------------------------------
#        augenrules              |          Yes          |  /etc/audit/rules.d/*.rules     |
#        augenrules              |          No           |  /etc/audit/rules.d/$key.rules  |
# -----------------------------------------------------------------------------------------
#
declare -a files_to_inspect

# First check sanity of the specified audit tool
if [ "$tool" != 'auditctl' ] && [ "$tool" != 'augenrules' ]
then
        echo "Unknown audit rules loading tool: $1. Aborting."
        echo "Use either 'auditctl' or 'augenrules'!"
        exit 1
# If audit tool is 'auditctl', then add '/etc/audit/audit.rules'
# file to the list of files to be inspected
elif [ "$tool" == 'auditctl' ]
then
        files_to_inspect=("${files_to_inspect[@]}" '/etc/audit/audit.rules' )
# If audit tool is 'augenrules', then check if the audit rule is defined
# If rule is defined, add '/etc/audit/rules.d/*.rules' to the list for inspection
# If rule isn't defined yet, add '/etc/audit/rules.d/$key.rules' to the list for inspection
elif [ "$tool" == 'augenrules' ]
then
        # Extract audit $key from audit rule so we can use it later
        key=$(expr "$full_rule" : '.*-k[[:space:]]\([^[:space:]]\+\)')
        # Check if particular audit rule is already defined
        IFS=$'\n' matches=($(sed -s -n -e "/${pattern}/!d" -e "/${arch}/!d" -e "/${group}/!d;F" /etc/audit/rules.d/*.rules))
        # Reset IFS back to default
        unset $IFS
        for match in "${matches[@]}"
        do
                files_to_inspect=("${files_to_inspect[@]}" "${match}")
        done
        # Case when particular rule isn't defined in /etc/audit/rules.d/*.rules yet
        if [ ${#files_to_inspect[@]} -eq "0" ]
        then
                files_to_inspect="/etc/audit/rules.d/$key.rules"
                if [ ! -e "$files_to_inspect" ]
                then
                        touch "$files_to_inspect"
                        chmod 0640 "$files_to_inspect"
                fi
        fi
fi

#
# Indicator that we want to append $full_rule into $audit_file by default
local append_expected_rule=0

for audit_file in "${files_to_inspect[@]}"
do

        # Filter existing $audit_file rules' definitions to select those that:
        # * follow the rule pattern, and
        # * meet the hardware architecture requirement, and
        # * are current syscall group specific
        IFS=$'\n' existing_rules=($(sed -e "/${pattern}/!d" -e "/${arch}/!d" -e "/${group}/!d"  "$audit_file"))
        # Reset IFS back to default
        unset $IFS

        # Process rules found case-by-case
        for rule in "${existing_rules[@]}"
        do
                # Found rule is for same arch & key, but differs (e.g. in count of -S arguments)
                if [ "${rule}" != "${full_rule}" ]
                then
                        # If so, isolate just '(-S \w)+' substring of that rule
                        rule_syscalls=$(echo $rule | grep -o -P '(-S \w+ )+')
                        # Check if list of '-S syscall' arguments of that rule is subset
                        # of '-S syscall' list of expected $full_rule
                        if grep -q -- "$rule_syscalls" <<< "$full_rule"
                        then
                                # Rule is covered (i.e. the list of -S syscalls for this rule is
                                # subset of -S syscalls of $full_rule => existing rule can be deleted
                                # Thus delete the rule from audit.rules & our array
                                sed -i -e "/$rule/d" "$audit_file"
                                existing_rules=("${existing_rules[@]//$rule/}")
                        else
                                # Rule isn't covered by $full_rule - it besides -S syscall arguments
                                # for this group contains also -S syscall arguments for other syscall
                                # group. Example: '-S lchown -S fchmod -S fchownat' => group='chown'
                                # since 'lchown' & 'fchownat' share 'chown' substring
                                # Therefore:
                                # * 1) delete the original rule from audit.rules
                                # (original '-S lchown -S fchmod -S fchownat' rule would be deleted)
                                # * 2) delete the -S syscall arguments for this syscall group, but
                                # keep those not belonging to this syscall group
                                # (original '-S lchown -S fchmod -S fchownat' would become '-S fchmod'
                                # * 3) append the modified (filtered) rule again into audit.rules
                                # if the same rule not already present
                                #
                                # 1) Delete the original rule
                                sed -i -e "/$rule/d" "$audit_file"
                                # 2) Delete syscalls for this group, but keep those from other groups
                                # Convert current rule syscall's string into array splitting by '-S' delimiter
                                IFS=$'-S' read -a rule_syscalls_as_array <<< "$rule_syscalls"
                                # Reset IFS back to default
                                unset $IFS
                                # Declare new empty string to hold '-S syscall' arguments from other groups
                                new_syscalls_for_rule=''
                                # Walk through existing '-S syscall' arguments
                                for syscall_arg in "${rule_syscalls_as_array[@]}"
                                do
                                        # Skip empty $syscall_arg values
                                        if [ "$syscall_arg" == '' ]
                                        then
                                                continue
                                        fi
                                        # If the '-S syscall' doesn't belong to current group add it to the new list
                                        # (together with adding '-S' delimiter back for each of such item found)
                                        if grep -q -v -- "$group" <<< "$syscall_arg"
                                        then
                                                new_syscalls_for_rule="$new_syscalls_for_rule -S $syscall_arg"
                                        fi
                                done
                                # Replace original '-S syscall' list with the new one for this rule
                                updated_rule=${rule//$rule_syscalls/$new_syscalls_for_rule}
                                # Squeeze repeated whitespace characters in rule definition (if any) into one
                                updated_rule=$(echo "$updated_rule" | tr -s '[:space:]')
                                # 3) Append the modified / filtered rule again into audit.rules
                                #    (but only in case it's not present yet to prevent duplicate definitions)
                                if ! grep -q -- "$updated_rule" "$audit_file"
                                then
                                        echo "$updated_rule" >> "$audit_file"
                                fi
                        fi
                else
                        # $audit_file already contains the expected rule form for this
                        # architecture & key => don't insert it second time
                        append_expected_rule=1
                fi
        done

        # We deleted all rules that were subset of the expected one for this arch & key.
        # Also isolated rules containing system calls not from this system calls group.
        # Now append the expected rule if it's not present in $audit_file yet
        if [[ ${append_expected_rule} -eq "0" ]]
        then
                echo "$full_rule" >> "$audit_file"
        fi
done

}

function rhel7_fedora_perform_audit_adjtimex_settimeofday_stime_remediation {

# Perform the remediation for the 'adjtimex', 'settimeofday', and 'stime' audit
# system calls on Red Hat Enterprise Linux 7 or Fedora OSes
#
# Retrieve hardware architecture of the underlying system
[ $(getconf LONG_BIT) = "32" ] && RULE_ARCHS=("b32") || RULE_ARCHS=("b32" "b64")

for ARCH in "${RULE_ARCHS[@]}"
do

        PATTERN="-a always,exit -F arch=${ARCH} -S .* -k *"
        # Create expected audit group and audit rule form for particular system call & architecture
        if [ ${ARCH} = "b32" ]
        then
                # stime system call is known at 32-bit arch (see e.g "$ ausyscall i386 stime" 's output)
                # so append it to the list of time group system calls to be audited
                GROUP="\(adjtimex\|settimeofday\|stime\)"
                FULL_RULE="-a always,exit -F arch=${ARCH} -S adjtimex -S settimeofday -S stime -k audit_time_rules"
        elif [ ${ARCH} = "b64" ]
        then
                # stime system call isn't known at 64-bit arch (see "$ ausyscall x86_64 stime" 's output)
                # therefore don't add it to the list of time group system calls to be audited
                GROUP="\(adjtimex\|settimeofday\)"
                FULL_RULE="-a always,exit -F arch=${ARCH} -S adjtimex -S settimeofday -k audit_time_rules"
        fi
        # Perform the remediation for both possible tools: 'auditctl' and 'augenrules'
        fix_audit_syscall_rule "auditctl" "$PATTERN" "$GROUP" "$ARCH" "$FULL_RULE"
        fix_audit_syscall_rule "augenrules" "$PATTERN" "$GROUP" "$ARCH" "$FULL_RULE"
done

}

rhel7_fedora_perform_audit_adjtimex_settimeofday_stime_remediation

Record attempts to alter time through settimeofday   [ref]rule

If the auditd daemon is configured to use the augenrules program to read audit rules during daemon startup (the default), add the following line to a file with suffix .rules in the directory /etc/audit/rules.d:

-a always,exit -F arch=b32 -S settimeofday -F key=audit_time_rules
If the system is 64 bit then also add the following line:
-a always,exit -F arch=b64 -S settimeofday -F key=audit_time_rules
If the auditd daemon is configured to use the auditctl utility to read audit rules during daemon startup, add the following line to /etc/audit/audit.rules file:
-a always,exit -F arch=b32 -S settimeofday -F key=audit_time_rules
If the system is 64 bit then also add the following line:
-a always,exit -F arch=b64 -S settimeofday -F key=audit_time_rules
The -k option allows for the specification of a key in string form that can be used for better reporting capability through ausearch and aureport. Multiple system calls can be defined on the same line to save space if desired, but is not required. See an example of multiple combined syscalls:
-a always,exit -F arch=b64 -S adjtimex,settimeofday -F key=audit_time_rules

Rationale:

Arbitrary changes to the system time can be used to obfuscate nefarious activities in log files, as well as to confuse network services that are highly dependent upon an accurate system time (such as sshd). All changes to the system time should be audited.

identifiers:  CCE-27216-1

references:  AC-17(7), AU-1(b), AU-2(a), AU-2(c), AU-2(d), AU-12(a), AU-12(c), IR-5, 5.2.4, Req-10.4.2.b, 1487, 169, 5.4.1.1, 3.1.7

Remediation Shell script:   (show)

Complexity:low
Disruption:low
Strategy:disable

function fix_audit_syscall_rule {

# Load function arguments into local variables
local tool="$1"
local pattern="$2"
local group="$3"
local arch="$4"
local full_rule="$5"

# Check sanity of the input
if [ $# -ne "5" ]
then
        echo "Usage: fix_audit_syscall_rule 'tool' 'pattern' 'group' 'arch' 'full rule'"
        echo "Aborting."
        exit 1
fi

# Create a list of audit *.rules files that should be inspected for presence and correctness
# of a particular audit rule. The scheme is as follows:
# 
# -----------------------------------------------------------------------------------------
#  Tool used to load audit rules | Rule already defined  |  Audit rules file to inspect    |
# -----------------------------------------------------------------------------------------
#        auditctl                |     Doesn't matter    |  /etc/audit/audit.rules         |
# -----------------------------------------------------------------------------------------
#        augenrules              |          Yes          |  /etc/audit/rules.d/*.rules     |
#        augenrules              |          No           |  /etc/audit/rules.d/$key.rules  |
# -----------------------------------------------------------------------------------------
#
declare -a files_to_inspect

# First check sanity of the specified audit tool
if [ "$tool" != 'auditctl' ] && [ "$tool" != 'augenrules' ]
then
        echo "Unknown audit rules loading tool: $1. Aborting."
        echo "Use either 'auditctl' or 'augenrules'!"
        exit 1
# If audit tool is 'auditctl', then add '/etc/audit/audit.rules'
# file to the list of files to be inspected
elif [ "$tool" == 'auditctl' ]
then
        files_to_inspect=("${files_to_inspect[@]}" '/etc/audit/audit.rules' )
# If audit tool is 'augenrules', then check if the audit rule is defined
# If rule is defined, add '/etc/audit/rules.d/*.rules' to the list for inspection
# If rule isn't defined yet, add '/etc/audit/rules.d/$key.rules' to the list for inspection
elif [ "$tool" == 'augenrules' ]
then
        # Extract audit $key from audit rule so we can use it later
        key=$(expr "$full_rule" : '.*-k[[:space:]]\([^[:space:]]\+\)')
        # Check if particular audit rule is already defined
        IFS=$'\n' matches=($(sed -s -n -e "/${pattern}/!d" -e "/${arch}/!d" -e "/${group}/!d;F" /etc/audit/rules.d/*.rules))
        # Reset IFS back to default
        unset $IFS
        for match in "${matches[@]}"
        do
                files_to_inspect=("${files_to_inspect[@]}" "${match}")
        done
        # Case when particular rule isn't defined in /etc/audit/rules.d/*.rules yet
        if [ ${#files_to_inspect[@]} -eq "0" ]
        then
                files_to_inspect="/etc/audit/rules.d/$key.rules"
                if [ ! -e "$files_to_inspect" ]
                then
                        touch "$files_to_inspect"
                        chmod 0640 "$files_to_inspect"
                fi
        fi
fi

#
# Indicator that we want to append $full_rule into $audit_file by default
local append_expected_rule=0

for audit_file in "${files_to_inspect[@]}"
do

        # Filter existing $audit_file rules' definitions to select those that:
        # * follow the rule pattern, and
        # * meet the hardware architecture requirement, and
        # * are current syscall group specific
        IFS=$'\n' existing_rules=($(sed -e "/${pattern}/!d" -e "/${arch}/!d" -e "/${group}/!d"  "$audit_file"))
        # Reset IFS back to default
        unset $IFS

        # Process rules found case-by-case
        for rule in "${existing_rules[@]}"
        do
                # Found rule is for same arch & key, but differs (e.g. in count of -S arguments)
                if [ "${rule}" != "${full_rule}" ]
                then
                        # If so, isolate just '(-S \w)+' substring of that rule
                        rule_syscalls=$(echo $rule | grep -o -P '(-S \w+ )+')
                        # Check if list of '-S syscall' arguments of that rule is subset
                        # of '-S syscall' list of expected $full_rule
                        if grep -q -- "$rule_syscalls" <<< "$full_rule"
                        then
                                # Rule is covered (i.e. the list of -S syscalls for this rule is
                                # subset of -S syscalls of $full_rule => existing rule can be deleted
                                # Thus delete the rule from audit.rules & our array
                                sed -i -e "/$rule/d" "$audit_file"
                                existing_rules=("${existing_rules[@]//$rule/}")
                        else
                                # Rule isn't covered by $full_rule - it besides -S syscall arguments
                                # for this group contains also -S syscall arguments for other syscall
                                # group. Example: '-S lchown -S fchmod -S fchownat' => group='chown'
                                # since 'lchown' & 'fchownat' share 'chown' substring
                                # Therefore:
                                # * 1) delete the original rule from audit.rules
                                # (original '-S lchown -S fchmod -S fchownat' rule would be deleted)
                                # * 2) delete the -S syscall arguments for this syscall group, but
                                # keep those not belonging to this syscall group
                                # (original '-S lchown -S fchmod -S fchownat' would become '-S fchmod'
                                # * 3) append the modified (filtered) rule again into audit.rules
                                # if the same rule not already present
                                #
                                # 1) Delete the original rule
                                sed -i -e "/$rule/d" "$audit_file"
                                # 2) Delete syscalls for this group, but keep those from other groups
                                # Convert current rule syscall's string into array splitting by '-S' delimiter
                                IFS=$'-S' read -a rule_syscalls_as_array <<< "$rule_syscalls"
                                # Reset IFS back to default
                                unset $IFS
                                # Declare new empty string to hold '-S syscall' arguments from other groups
                                new_syscalls_for_rule=''
                                # Walk through existing '-S syscall' arguments
                                for syscall_arg in "${rule_syscalls_as_array[@]}"
                                do
                                        # Skip empty $syscall_arg values
                                        if [ "$syscall_arg" == '' ]
                                        then
                                                continue
                                        fi
                                        # If the '-S syscall' doesn't belong to current group add it to the new list
                                        # (together with adding '-S' delimiter back for each of such item found)
                                        if grep -q -v -- "$group" <<< "$syscall_arg"
                                        then
                                                new_syscalls_for_rule="$new_syscalls_for_rule -S $syscall_arg"
                                        fi
                                done
                                # Replace original '-S syscall' list with the new one for this rule
                                updated_rule=${rule//$rule_syscalls/$new_syscalls_for_rule}
                                # Squeeze repeated whitespace characters in rule definition (if any) into one
                                updated_rule=$(echo "$updated_rule" | tr -s '[:space:]')
                                # 3) Append the modified / filtered rule again into audit.rules
                                #    (but only in case it's not present yet to prevent duplicate definitions)
                                if ! grep -q -- "$updated_rule" "$audit_file"
                                then
                                        echo "$updated_rule" >> "$audit_file"
                                fi
                        fi
                else
                        # $audit_file already contains the expected rule form for this
                        # architecture & key => don't insert it second time
                        append_expected_rule=1
                fi
        done

        # We deleted all rules that were subset of the expected one for this arch & key.
        # Also isolated rules containing system calls not from this system calls group.
        # Now append the expected rule if it's not present in $audit_file yet
        if [[ ${append_expected_rule} -eq "0" ]]
        then
                echo "$full_rule" >> "$audit_file"
        fi
done

}

function rhel7_fedora_perform_audit_adjtimex_settimeofday_stime_remediation {

# Perform the remediation for the 'adjtimex', 'settimeofday', and 'stime' audit
# system calls on Red Hat Enterprise Linux 7 or Fedora OSes
#
# Retrieve hardware architecture of the underlying system
[ $(getconf LONG_BIT) = "32" ] && RULE_ARCHS=("b32") || RULE_ARCHS=("b32" "b64")

for ARCH in "${RULE_ARCHS[@]}"
do

        PATTERN="-a always,exit -F arch=${ARCH} -S .* -k *"
        # Create expected audit group and audit rule form for particular system call & architecture
        if [ ${ARCH} = "b32" ]
        then
                # stime system call is known at 32-bit arch (see e.g "$ ausyscall i386 stime" 's output)
                # so append it to the list of time group system calls to be audited
                GROUP="\(adjtimex\|settimeofday\|stime\)"
                FULL_RULE="-a always,exit -F arch=${ARCH} -S adjtimex -S settimeofday -S stime -k audit_time_rules"
        elif [ ${ARCH} = "b64" ]
        then
                # stime system call isn't known at 64-bit arch (see "$ ausyscall x86_64 stime" 's output)
                # therefore don't add it to the list of time group system calls to be audited
                GROUP="\(adjtimex\|settimeofday\)"
                FULL_RULE="-a always,exit -F arch=${ARCH} -S adjtimex -S settimeofday -k audit_time_rules"
        fi
        # Perform the remediation for both possible tools: 'auditctl' and 'augenrules'
        fix_audit_syscall_rule "auditctl" "$PATTERN" "$GROUP" "$ARCH" "$FULL_RULE"
        fix_audit_syscall_rule "augenrules" "$PATTERN" "$GROUP" "$ARCH" "$FULL_RULE"
done

}

rhel7_fedora_perform_audit_adjtimex_settimeofday_stime_remediation

Record Attempts to Alter Time Through stime   [ref]rule

If the auditd daemon is configured to use the augenrules program to read audit rules during daemon startup (the default), add the following line to a file with suffix .rules in the directory /etc/audit/rules.d for both 32 bit and 64 bit systems:

-a always,exit -F arch=b32 -S stime -F key=audit_time_rules
Since the 64 bit version of the "stime" system call is not defined in the audit lookup table, the corresponding "-F arch=b64" form of this rule is not expected to be defined on 64 bit systems (the aforementioned "-F arch=b32" stime rule form itself is sufficient for both 32 bit and 64 bit systems). If the auditd daemon is configured to use the auditctl utility to read audit rules during daemon startup, add the following line to /etc/audit/audit.rules file for both 32 bit and 64 bit systems:
-a always,exit -F arch=b32 -S stime -F key=audit_time_rules
Since the 64 bit version of the "stime" system call is not defined in the audit lookup table, the corresponding "-F arch=b64" form of this rule is not expected to be defined on 64 bit systems (the aforementioned "-F arch=b32" stime rule form itself is sufficient for both 32 bit and 64 bit systems). The -k option allows for the specification of a key in string form that can be used for better reporting capability through ausearch and aureport. Multiple system calls can be defined on the same line to save space if desired, but is not required. See an example of multiple combined system calls:
-a always,exit -F arch=b64 -S adjtimex,settimeofday -F key=audit_time_rules

Rationale:

Arbitrary changes to the system time can be used to obfuscate nefarious activities in log files, as well as to confuse network services that are highly dependent upon an accurate system time (such as sshd). All changes to the system time should be audited.

identifiers:  CCE-27299-7

references:  AC-17(7), AU-1(b), AU-2(a), AU-2(c), AU-2(d), AU-12(a), AU-12(c), IR-5, Req-10.4.2.b, 1487, 169, 5.4.1.1, 3.1.7

Remediation Shell script:   (show)

Complexity:low
Disruption:low
Strategy:disable

function fix_audit_syscall_rule {

# Load function arguments into local variables
local tool="$1"
local pattern="$2"
local group="$3"
local arch="$4"
local full_rule="$5"

# Check sanity of the input
if [ $# -ne "5" ]
then
        echo "Usage: fix_audit_syscall_rule 'tool' 'pattern' 'group' 'arch' 'full rule'"
        echo "Aborting."
        exit 1
fi

# Create a list of audit *.rules files that should be inspected for presence and correctness
# of a particular audit rule. The scheme is as follows:
# 
# -----------------------------------------------------------------------------------------
#  Tool used to load audit rules | Rule already defined  |  Audit rules file to inspect    |
# -----------------------------------------------------------------------------------------
#        auditctl                |     Doesn't matter    |  /etc/audit/audit.rules         |
# -----------------------------------------------------------------------------------------
#        augenrules              |          Yes          |  /etc/audit/rules.d/*.rules     |
#        augenrules              |          No           |  /etc/audit/rules.d/$key.rules  |
# -----------------------------------------------------------------------------------------
#
declare -a files_to_inspect

# First check sanity of the specified audit tool
if [ "$tool" != 'auditctl' ] && [ "$tool" != 'augenrules' ]
then
        echo "Unknown audit rules loading tool: $1. Aborting."
        echo "Use either 'auditctl' or 'augenrules'!"
        exit 1
# If audit tool is 'auditctl', then add '/etc/audit/audit.rules'
# file to the list of files to be inspected
elif [ "$tool" == 'auditctl' ]
then
        files_to_inspect=("${files_to_inspect[@]}" '/etc/audit/audit.rules' )
# If audit tool is 'augenrules', then check if the audit rule is defined
# If rule is defined, add '/etc/audit/rules.d/*.rules' to the list for inspection
# If rule isn't defined yet, add '/etc/audit/rules.d/$key.rules' to the list for inspection
elif [ "$tool" == 'augenrules' ]
then
        # Extract audit $key from audit rule so we can use it later
        key=$(expr "$full_rule" : '.*-k[[:space:]]\([^[:space:]]\+\)')
        # Check if particular audit rule is already defined
        IFS=$'\n' matches=($(sed -s -n -e "/${pattern}/!d" -e "/${arch}/!d" -e "/${group}/!d;F" /etc/audit/rules.d/*.rules))
        # Reset IFS back to default
        unset $IFS
        for match in "${matches[@]}"
        do
                files_to_inspect=("${files_to_inspect[@]}" "${match}")
        done
        # Case when particular rule isn't defined in /etc/audit/rules.d/*.rules yet
        if [ ${#files_to_inspect[@]} -eq "0" ]
        then
                files_to_inspect="/etc/audit/rules.d/$key.rules"
                if [ ! -e "$files_to_inspect" ]
                then
                        touch "$files_to_inspect"
                        chmod 0640 "$files_to_inspect"
                fi
        fi
fi

#
# Indicator that we want to append $full_rule into $audit_file by default
local append_expected_rule=0

for audit_file in "${files_to_inspect[@]}"
do

        # Filter existing $audit_file rules' definitions to select those that:
        # * follow the rule pattern, and
        # * meet the hardware architecture requirement, and
        # * are current syscall group specific
        IFS=$'\n' existing_rules=($(sed -e "/${pattern}/!d" -e "/${arch}/!d" -e "/${group}/!d"  "$audit_file"))
        # Reset IFS back to default
        unset $IFS

        # Process rules found case-by-case
        for rule in "${existing_rules[@]}"
        do
                # Found rule is for same arch & key, but differs (e.g. in count of -S arguments)
                if [ "${rule}" != "${full_rule}" ]
                then
                        # If so, isolate just '(-S \w)+' substring of that rule
                        rule_syscalls=$(echo $rule | grep -o -P '(-S \w+ )+')
                        # Check if list of '-S syscall' arguments of that rule is subset
                        # of '-S syscall' list of expected $full_rule
                        if grep -q -- "$rule_syscalls" <<< "$full_rule"
                        then
                                # Rule is covered (i.e. the list of -S syscalls for this rule is
                                # subset of -S syscalls of $full_rule => existing rule can be deleted
                                # Thus delete the rule from audit.rules & our array
                                sed -i -e "/$rule/d" "$audit_file"
                                existing_rules=("${existing_rules[@]//$rule/}")
                        else
                                # Rule isn't covered by $full_rule - it besides -S syscall arguments
                                # for this group contains also -S syscall arguments for other syscall
                                # group. Example: '-S lchown -S fchmod -S fchownat' => group='chown'
                                # since 'lchown' & 'fchownat' share 'chown' substring
                                # Therefore:
                                # * 1) delete the original rule from audit.rules
                                # (original '-S lchown -S fchmod -S fchownat' rule would be deleted)
                                # * 2) delete the -S syscall arguments for this syscall group, but
                                # keep those not belonging to this syscall group
                                # (original '-S lchown -S fchmod -S fchownat' would become '-S fchmod'
                                # * 3) append the modified (filtered) rule again into audit.rules
                                # if the same rule not already present
                                #
                                # 1) Delete the original rule
                                sed -i -e "/$rule/d" "$audit_file"
                                # 2) Delete syscalls for this group, but keep those from other groups
                                # Convert current rule syscall's string into array splitting by '-S' delimiter
                                IFS=$'-S' read -a rule_syscalls_as_array <<< "$rule_syscalls"
                                # Reset IFS back to default
                                unset $IFS
                                # Declare new empty string to hold '-S syscall' arguments from other groups
                                new_syscalls_for_rule=''
                                # Walk through existing '-S syscall' arguments
                                for syscall_arg in "${rule_syscalls_as_array[@]}"
                                do
                                        # Skip empty $syscall_arg values
                                        if [ "$syscall_arg" == '' ]
                                        then
                                                continue
                                        fi
                                        # If the '-S syscall' doesn't belong to current group add it to the new list
                                        # (together with adding '-S' delimiter back for each of such item found)
                                        if grep -q -v -- "$group" <<< "$syscall_arg"
                                        then
                                                new_syscalls_for_rule="$new_syscalls_for_rule -S $syscall_arg"
                                        fi
                                done
                                # Replace original '-S syscall' list with the new one for this rule
                                updated_rule=${rule//$rule_syscalls/$new_syscalls_for_rule}
                                # Squeeze repeated whitespace characters in rule definition (if any) into one
                                updated_rule=$(echo "$updated_rule" | tr -s '[:space:]')
                                # 3) Append the modified / filtered rule again into audit.rules
                                #    (but only in case it's not present yet to prevent duplicate definitions)
                                if ! grep -q -- "$updated_rule" "$audit_file"
                                then
                                        echo "$updated_rule" >> "$audit_file"
                                fi
                        fi
                else
                        # $audit_file already contains the expected rule form for this
                        # architecture & key => don't insert it second time
                        append_expected_rule=1
                fi
        done

        # We deleted all rules that were subset of the expected one for this arch & key.
        # Also isolated rules containing system calls not from this system calls group.
        # Now append the expected rule if it's not present in $audit_file yet
        if [[ ${append_expected_rule} -eq "0" ]]
        then
                echo "$full_rule" >> "$audit_file"
        fi
done

}

function rhel7_fedora_perform_audit_adjtimex_settimeofday_stime_remediation {

# Perform the remediation for the 'adjtimex', 'settimeofday', and 'stime' audit
# system calls on Red Hat Enterprise Linux 7 or Fedora OSes
#
# Retrieve hardware architecture of the underlying system
[ $(getconf LONG_BIT) = "32" ] && RULE_ARCHS=("b32") || RULE_ARCHS=("b32" "b64")

for ARCH in "${RULE_ARCHS[@]}"
do

        PATTERN="-a always,exit -F arch=${ARCH} -S .* -k *"
        # Create expected audit group and audit rule form for particular system call & architecture
        if [ ${ARCH} = "b32" ]
        then
                # stime system call is known at 32-bit arch (see e.g "$ ausyscall i386 stime" 's output)
                # so append it to the list of time group system calls to be audited
                GROUP="\(adjtimex\|settimeofday\|stime\)"
                FULL_RULE="-a always,exit -F arch=${ARCH} -S adjtimex -S settimeofday -S stime -k audit_time_rules"
        elif [ ${ARCH} = "b64" ]
        then
                # stime system call isn't known at 64-bit arch (see "$ ausyscall x86_64 stime" 's output)
                # therefore don't add it to the list of time group system calls to be audited
                GROUP="\(adjtimex\|settimeofday\)"
                FULL_RULE="-a always,exit -F arch=${ARCH} -S adjtimex -S settimeofday -k audit_time_rules"
        fi
        # Perform the remediation for both possible tools: 'auditctl' and 'augenrules'
        fix_audit_syscall_rule "auditctl" "$PATTERN" "$GROUP" "$ARCH" "$FULL_RULE"
        fix_audit_syscall_rule "augenrules" "$PATTERN" "$GROUP" "$ARCH" "$FULL_RULE"
done

}

rhel7_fedora_perform_audit_adjtimex_settimeofday_stime_remediation

Record Attempts to Alter Time Through clock_settime   [ref]rule

If the auditd daemon is configured to use the augenrules program to read audit rules during daemon startup (the default), add the following line to a file with suffix .rules in the directory /etc/audit/rules.d:

-a always,exit -F arch=b32 -S clock_settime -F a0=0x0 -F key=time-change
If the system is 64 bit then also add the following line:
-a always,exit -F arch=b64 -S clock_settime -F a0=0x0 -F key=time-change
If the auditd daemon is configured to use the auditctl utility to read audit rules during daemon startup, add the following line to /etc/audit/audit.rules file:
-a always,exit -F arch=b32 -S clock_settime -F a0=0x0 -F key=time-change
If the system is 64 bit then also add the following line:
-a always,exit -F arch=b64 -S clock_settime -F a0=0x0 -F key=time-change
The -k option allows for the specification of a key in string form that can be used for better reporting capability through ausearch and aureport. Multiple system calls can be defined on the same line to save space if desired, but is not required. See an example of multiple combined syscalls:
-a always,exit -F arch=b64 -S adjtimex,settimeofday -F key=audit_time_rules

Rationale:

Arbitrary changes to the system time can be used to obfuscate nefarious activities in log files, as well as to confuse network services that are highly dependent upon an accurate system time (such as sshd). All changes to the system time should be audited.

identifiers:  CCE-27219-5

references:  AC-17(7), AU-1(b), AU-2(a), AU-2(c), AU-2(d), AU-12(a), AU-12(c), IR-5, 5.2.4, Req-10.4.2.b, 1487, 169, 5.4.1.1, 3.1.7

Remediation Shell script:   (show)

Complexity:low
Disruption:low
Strategy:disable


# First perform the remediation of the syscall rule
# Retrieve hardware architecture of the underlying system
[ "$(getconf LONG_BIT)" = "32" ] && RULE_ARCHS=("b32") || RULE_ARCHS=("b32" "b64")

for ARCH in "${RULE_ARCHS[@]}"
do
	PATTERN="-a always,exit -F arch=$ARCH -S clock_settime -F a0=.* \(-F key=\|-k \).*"
	GROUP="clock_settime"
	FULL_RULE="-a always,exit -F arch=$ARCH -S clock_settime -F a0=0x0 -k time-change"
	# Perform the remediation for both possible tools: 'auditctl' and 'augenrules'

function fix_audit_syscall_rule {

# Load function arguments into local variables
local tool="$1"
local pattern="$2"
local group="$3"
local arch="$4"
local full_rule="$5"

# Check sanity of the input
if [ $# -ne "5" ]
then
        echo "Usage: fix_audit_syscall_rule 'tool' 'pattern' 'group' 'arch' 'full rule'"
        echo "Aborting."
        exit 1
fi

# Create a list of audit *.rules files that should be inspected for presence and correctness
# of a particular audit rule. The scheme is as follows:
#
# -----------------------------------------------------------------------------------------
#  Tool used to load audit rules | Rule already defined  |  Audit rules file to inspect    |
# -----------------------------------------------------------------------------------------
#        auditctl                |     Doesn't matter    |  /etc/audit/audit.rules         |
# -----------------------------------------------------------------------------------------
#        augenrules              |          Yes          |  /etc/audit/rules.d/*.rules     |
#        augenrules              |          No           |  /etc/audit/rules.d/$key.rules  |
# -----------------------------------------------------------------------------------------
#
declare -a files_to_inspect

# First check sanity of the specified audit tool
if [ "$tool" != 'auditctl' ] && [ "$tool" != 'augenrules' ]
then
        echo "Unknown audit rules loading tool: $1. Aborting."
        echo "Use either 'auditctl' or 'augenrules'!"
        exit 1
# If audit tool is 'auditctl', then add '/etc/audit/audit.rules'
# file to the list of files to be inspected
elif [ "$tool" == 'auditctl' ]
then
        files_to_inspect=("${files_to_inspect[@]}" '/etc/audit/audit.rules' )
# If audit tool is 'augenrules', then check if the audit rule is defined
# If rule is defined, add '/etc/audit/rules.d/*.rules' to the list for inspection
# If rule isn't defined yet, add '/etc/audit/rules.d/$key.rules' to the list for inspection
elif [ "$tool" == 'augenrules' ]
then
        # Extract audit $key from audit rule so we can use it later
        key=$(expr "$full_rule" : '.*-k[[:space:]]\([^[:space:]]\+\)')
        # Check if particular audit rule is already defined
        IFS=$'\n' matches=($(sed -s -n -e "/${pattern}/!d" -e "/${arch}/!d" -e "/${group}/!d;F" /etc/audit/rules.d/*.rules))
        # Reset IFS back to default
        unset $IFS
        for match in "${matches[@]}"
        do
                files_to_inspect=("${files_to_inspect[@]}" "${match}")
        done
        # Case when particular rule isn't defined in /etc/audit/rules.d/*.rules yet
        if [ ${#files_to_inspect[@]} -eq "0" ]
        then
                files_to_inspect="/etc/audit/rules.d/$key.rules"
                if [ ! -e "$files_to_inspect" ]
                then
                        touch "$files_to_inspect"
                        chmod 0640 "$files_to_inspect"
                fi
        fi
fi

#
# Indicator that we want to append $full_rule into $audit_file by default
local append_expected_rule=0

for audit_file in "${files_to_inspect[@]}"
do

        # Filter existing $audit_file rules' definitions to select those that:
        # * follow the rule pattern, and
        # * meet the hardware architecture requirement, and
        # * are current syscall group specific
        IFS=$'\n' existing_rules=($(sed -e "/${pattern}/!d" -e "/${arch}/!d" -e "/${group}/!d"  "$audit_file"))
        # Reset IFS back to default
        unset $IFS

        # Process rules found case-by-case
        for rule in "${existing_rules[@]}"
        do
                # Found rule is for same arch & key, but differs (e.g. in count of -S arguments)
                if [ "${rule}" != "${full_rule}" ]
                then
                        # If so, isolate just '(-S \w)+' substring of that rule
                        rule_syscalls=$(echo $rule | grep -o -P '(-S \w+ )+')
                        # Check if list of '-S syscall' arguments of that rule is subset
                        # of '-S syscall' list of expected $full_rule
                        if grep -q -- "$rule_syscalls" <<< "$full_rule"
                        then
                                # Rule is covered (i.e. the list of -S syscalls for this rule is
                                # subset of -S syscalls of $full_rule => existing rule can be deleted
                                # Thus delete the rule from audit.rules & our array
                                sed -i -e "/$rule/d" "$audit_file"
                                existing_rules=("${existing_rules[@]//$rule/}")
                        else
                                # Rule isn't covered by $full_rule - it besides -S syscall arguments
                                # for this group contains also -S syscall arguments for other syscall
                                # group. Example: '-S lchown -S fchmod -S fchownat' => group='chown'
                                # since 'lchown' & 'fchownat' share 'chown' substring
                                # Therefore:
                                # * 1) delete the original rule from audit.rules
                                # (original '-S lchown -S fchmod -S fchownat' rule would be deleted)
                                # * 2) delete the -S syscall arguments for this syscall group, but
                                # keep those not belonging to this syscall group
                                # (original '-S lchown -S fchmod -S fchownat' would become '-S fchmod'
                                # * 3) append the modified (filtered) rule again into audit.rules
                                # if the same rule not already present
                                #
                                # 1) Delete the original rule
                                sed -i -e "/$rule/d" "$audit_file"
                                # 2) Delete syscalls for this group, but keep those from other groups
                                # Convert current rule syscall's string into array splitting by '-S' delimiter
                                IFS=$'-S' read -a rule_syscalls_as_array <<< "$rule_syscalls"
                                # Reset IFS back to default
                                unset $IFS
                                # Declare new empty string to hold '-S syscall' arguments from other groups
                                new_syscalls_for_rule=''
                                # Walk through existing '-S syscall' arguments
                                for syscall_arg in "${rule_syscalls_as_array[@]}"
                                do
                                        # Skip empty $syscall_arg values
                                        if [ "$syscall_arg" == '' ]
                                        then
                                                continue
                                        fi
                                        # If the '-S syscall' doesn't belong to current group add it to the new list
                                        # (together with adding '-S' delimiter back for each of such item found)
                                        if grep -q -v -- "$group" <<< "$syscall_arg"
                                        then
                                                new_syscalls_for_rule="$new_syscalls_for_rule -S $syscall_arg"
                                        fi
                                done
                                # Replace original '-S syscall' list with the new one for this rule
                                updated_rule=${rule//$rule_syscalls/$new_syscalls_for_rule}
                                # Squeeze repeated whitespace characters in rule definition (if any) into one
                                updated_rule=$(echo "$updated_rule" | tr -s '[:space:]')
                                # 3) Append the modified / filtered rule again into audit.rules
                                #    (but only in case it's not present yet to prevent duplicate definitions)
                                if ! grep -q -- "$updated_rule" "$audit_file"
                                then
                                        echo "$updated_rule" >> "$audit_file"
                                fi
                        fi
                else
                        # $audit_file already contains the expected rule form for this
                        # architecture & key => don't insert it second time
                        append_expected_rule=1
                fi
        done

        # We deleted all rules that were subset of the expected one for this arch & key.
        # Also isolated rules containing system calls not from this system calls group.
        # Now append the expected rule if it's not present in $audit_file yet
        if [[ ${append_expected_rule} -eq "0" ]]
        then
                echo "$full_rule" >> "$audit_file"
        fi
done

}

	fix_audit_syscall_rule "auditctl" "$PATTERN" "$GROUP" "$ARCH" "$FULL_RULE"
	fix_audit_syscall_rule "augenrules" "$PATTERN" "$GROUP" "$ARCH" "$FULL_RULE"
done

Record Attempts to Alter the localtime File   [ref]rule

If the auditd daemon is configured to use the augenrules program to read audit rules during daemon startup (the default), add the following line to a file with suffix .rules in the directory /etc/audit/rules.d:

-w /etc/localtime -p wa -k audit_time_rules
If the auditd daemon is configured to use the auditctl utility to read audit rules during daemon startup, add the following line to /etc/audit/audit.rules file:
-w /etc/localtime -p wa -k audit_time_rules
The -k option allows for the specification of a key in string form that can be used for better reporting capability through ausearch and aureport and should always be used.

Rationale:

Arbitrary changes to the system time can be used to obfuscate nefarious activities in log files, as well as to confuse network services that are highly dependent upon an accurate system time (such as sshd). All changes to the system time should be audited.

identifiers:  CCE-27310-2

references:  AC-17(7), AU-1(b), AU-2(a), AU-2(c), AU-2(d), AU-12(a), AU-12(b), IR-5, 5.2.4, Req-10.4.2.b, 1487, 169, 5.4.1.1, 3.1.7

Remediation Shell script:   (show)

Complexity:low
Disruption:low
Strategy:disable


# Perform the remediation for both possible tools: 'auditctl' and 'augenrules'

function fix_audit_watch_rule {

# Load function arguments into local variables
local tool="$1"
local path="$2"
local required_access_bits="$3"
local key="$4"

# Check sanity of the input
if [ $# -ne "4" ]
then
        echo "Usage: fix_audit_watch_rule 'tool' 'path' 'bits' 'key'"
        echo "Aborting."
        exit 1
fi

# Create a list of audit *.rules files that should be inspected for presence and correctness
# of a particular audit rule. The scheme is as follows:
#
# -----------------------------------------------------------------------------------------
# Tool used to load audit rules | Rule already defined  |  Audit rules file to inspect    |
# -----------------------------------------------------------------------------------------
#       auditctl                |     Doesn't matter    |  /etc/audit/audit.rules         |
# -----------------------------------------------------------------------------------------
#       augenrules              |          Yes          |  /etc/audit/rules.d/*.rules     |
#       augenrules              |          No           |  /etc/audit/rules.d/$key.rules  |
# -----------------------------------------------------------------------------------------
declare -a files_to_inspect

# Check sanity of the specified audit tool
if [ "$tool" != 'auditctl' ] && [ "$tool" != 'augenrules' ]
then
        echo "Unknown audit rules loading tool: $1. Aborting."
        echo "Use either 'auditctl' or 'augenrules'!"
        exit 1
# If the audit tool is 'auditctl', then add '/etc/audit/audit.rules'
# into the list of files to be inspected
elif [ "$tool" == 'auditctl' ]
then
        files_to_inspect=("${files_to_inspect[@]}" '/etc/audit/audit.rules')
# If the audit is 'augenrules', then check if rule is already defined
# If rule is defined, add '/etc/audit/rules.d/*.rules' to list of files for inspection.
# If rule isn't defined, add '/etc/audit/rules.d/$key.rules' to list of files for inspection.
elif [ "$tool" == 'augenrules' ]
then
        # Case when particular audit rule is already defined in some of /etc/audit/rules.d/*.rules file
        # Get pair -- filepath : matching_row into @matches array
        IFS=$'\n' matches=($(grep -P "[\s]*-w[\s]+$path" /etc/audit/rules.d/*.rules))
        # Reset IFS back to default
        unset $IFS
        # For each of the matched entries
        for match in "${matches[@]}"
        do
                # Extract filepath from the match
                rulesd_audit_file=$(echo $match | cut -f1 -d ':')
                # Append that path into list of files for inspection
                files_to_inspect=("${files_to_inspect[@]}" "$rulesd_audit_file")
        done
        # Case when particular audit rule isn't defined yet
        if [ ${#files_to_inspect[@]} -eq "0" ]
        then
                # Append '/etc/audit/rules.d/$key.rules' into list of files for inspection
                files_to_inspect="/etc/audit/rules.d/$key.rules"
                # If the $key.rules file doesn't exist yet, create it with correct permissions
                if [ ! -e "$files_to_inspect" ]
                then
                        touch "$files_to_inspect"
                        chmod 0640 "$files_to_inspect"
                fi
        fi
fi

# Finally perform the inspection and possible subsequent audit rule
# correction for each of the files previously identified for inspection
for audit_rules_file in "${files_to_inspect[@]}"
do

        # Check if audit watch file system object rule for given path already present
        if grep -q -P -- "[\s]*-w[\s]+$path" "$audit_rules_file"
        then
                # Rule is found => verify yet if existing rule definition contains
                # all of the required access type bits

                # Escape slashes in path for use in sed pattern below
                local esc_path=${path//$'/'/$'\/'}
                # Define BRE whitespace class shortcut
                local sp="[[:space:]]"
                # Extract current permission access types (e.g. -p [r|w|x|a] values) from audit rule
                current_access_bits=$(sed -ne "s/$sp*-w$sp\+$esc_path$sp\+-p$sp\+\([rxwa]\{1,4\}\).*/\1/p" "$audit_rules_file")
                # Split required access bits string into characters array
                # (to check bit's presence for one bit at a time)
                for access_bit in $(echo "$required_access_bits" | grep -o .)
                do
                        # For each from the required access bits (e.g. 'w', 'a') check
                        # if they are already present in current access bits for rule.
                        # If not, append that bit at the end
                        if ! grep -q "$access_bit" <<< "$current_access_bits"
                        then
                                # Concatenate the existing mask with the missing bit
                                current_access_bits="$current_access_bits$access_bit"
                        fi
                done
                # Propagate the updated rule's access bits (original + the required
                # ones) back into the /etc/audit/audit.rules file for that rule
                sed -i "s/\($sp*-w$sp\+$esc_path$sp\+-p$sp\+\)\([rxwa]\{1,4\}\)\(.*\)/\1$current_access_bits\3/" "$audit_rules_file"
        else
                # Rule isn't present yet. Append it at the end of $audit_rules_file file
                # with proper key

                echo "-w $path -p $required_access_bits -k $key" >> "$audit_rules_file"
        fi
done
}

fix_audit_watch_rule "auditctl" "/etc/localtime" "wa" "audit_time_rules"
fix_audit_watch_rule "augenrules" "/etc/localtime" "wa" "audit_time_rules"

Record Events that Modify the System's Discretionary Access Controls   [ref]group

At a minimum, the audit system should collect file permission changes for all users and root. Note that the "-F arch=b32" lines should be present even on a 64 bit system. These commands identify system calls for auditing. Even if the system is 64 bit it can still execute 32 bit system calls. Additionally, these rules can be configured in a number of ways while still achieving the desired effect. An example of this is that the "-S" calls could be split up and placed on separate lines, however, this is less efficient. Add the following to /etc/audit/audit.rules:

-a always,exit -F arch=b32 -S chmod,fchmod,fchmodat -F auid>=1000 -F auid!=4294967295 -F key=perm_mod
    -a always,exit -F arch=b32 -S chown,fchown,fchownat,lchown -F auid>=1000 -F auid!=4294967295 -F key=perm_mod
    -a always,exit -F arch=b32 -S setxattr,lsetxattr,fsetxattr,removexattr,lremovexattr,fremovexattr -F auid>=1000 -F auid!=4294967295 -F key=perm_mod
If your system is 64 bit then these lines should be duplicated and the arch=b32 replaced with arch=b64 as follows:
-a always,exit -F arch=b64 -S chmod,fchmod,fchmodat -F auid>=1000 -F auid!=4294967295 -F key=perm_mod
    -a always,exit -F arch=b64 -S chown,fchown,fchownat,lchown -F auid>=1000 -F auid!=4294967295 -F key=perm_mod
    -a always,exit -F arch=b64 -S setxattr,lsetxattr,fsetxattr,removexattr,lremovexattr,fremovexattr -F auid>=1000 -F auid!=4294967295 -F key=perm_mod

contains 13 rules

Record Events that Modify the System's Discretionary Access Controls - chmod   [ref]rule

At a minimum, the audit system should collect file permission changes for all users and root. If the auditd daemon is configured to use the augenrules program to read audit rules during daemon startup (the default), add the following line to a file with suffix .rules in the directory /etc/audit/rules.d:

-a always,exit -F arch=b32 -S chmod -F auid>=1000 -F auid!=4294967295 -F key=perm_mod
If the system is 64 bit then also add the following line:
-a always,exit -F arch=b64 -S chmod -F auid>=1000 -F auid!=4294967295 -F key=perm_mod
If the auditd daemon is configured to use the auditctl utility to read audit rules during daemon startup, add the following line to /etc/audit/audit.rules file:
-a always,exit -F arch=b32 -S chmod -F auid>=1000 -F auid!=4294967295 -F key=perm_mod
If the system is 64 bit then also add the following line:
-a always,exit -F arch=b64 -S chmod -F auid>=1000 -F auid!=4294967295 -F key=perm_mod

warning  Note that these rules can be configured in a number of ways while still achieving the desired effect. Here the system calls have been placed independent of other system calls. Grouping these system calls with others as identifying earlier in this guide is more efficient.
Rationale:

The changing of file permissions could indicate that a user is attempting to gain access to information that would otherwise be disallowed. Auditing DAC modifications can facilitate the identification of patterns of abuse among both authorized and unauthorized users.

Remediation Shell script:   (show)

Complexity:low
Disruption:low
Strategy:disable


# Perform the remediation for the syscall rule
# Retrieve hardware architecture of the underlying system
[ $(getconf LONG_BIT) = "32" ] && RULE_ARCHS=("b32") || RULE_ARCHS=("b32" "b64")

for ARCH in "${RULE_ARCHS[@]}"
do
	PATTERN="-a always,exit -F arch=$ARCH -S .* -F auid>=1000 -F auid!=4294967295 -k *"
	GROUP="chmod"
	FULL_RULE="-a always,exit -F arch=$ARCH -S chmod -S fchmod -S fchmodat -F auid>=1000 -F auid!=4294967295 -k perm_mod"
	# Perform the remediation for both possible tools: 'auditctl' and 'augenrules'

function fix_audit_syscall_rule {

# Load function arguments into local variables
local tool="$1"
local pattern="$2"
local group="$3"
local arch="$4"
local full_rule="$5"

# Check sanity of the input
if [ $# -ne "5" ]
then
        echo "Usage: fix_audit_syscall_rule 'tool' 'pattern' 'group' 'arch' 'full rule'"
        echo "Aborting."
        exit 1
fi

# Create a list of audit *.rules files that should be inspected for presence and correctness
# of a particular audit rule. The scheme is as follows:
#
# -----------------------------------------------------------------------------------------
#  Tool used to load audit rules | Rule already defined  |  Audit rules file to inspect    |
# -----------------------------------------------------------------------------------------
#        auditctl                |     Doesn't matter    |  /etc/audit/audit.rules         |
# -----------------------------------------------------------------------------------------
#        augenrules              |          Yes          |  /etc/audit/rules.d/*.rules     |
#        augenrules              |          No           |  /etc/audit/rules.d/$key.rules  |
# -----------------------------------------------------------------------------------------
#
declare -a files_to_inspect

# First check sanity of the specified audit tool
if [ "$tool" != 'auditctl' ] && [ "$tool" != 'augenrules' ]
then
        echo "Unknown audit rules loading tool: $1. Aborting."
        echo "Use either 'auditctl' or 'augenrules'!"
        exit 1
# If audit tool is 'auditctl', then add '/etc/audit/audit.rules'
# file to the list of files to be inspected
elif [ "$tool" == 'auditctl' ]
then
        files_to_inspect=("${files_to_inspect[@]}" '/etc/audit/audit.rules' )
# If audit tool is 'augenrules', then check if the audit rule is defined
# If rule is defined, add '/etc/audit/rules.d/*.rules' to the list for inspection
# If rule isn't defined yet, add '/etc/audit/rules.d/$key.rules' to the list for inspection
elif [ "$tool" == 'augenrules' ]
then
        # Extract audit $key from audit rule so we can use it later
        key=$(expr "$full_rule" : '.*-k[[:space:]]\([^[:space:]]\+\)')
        # Check if particular audit rule is already defined
        IFS=$'\n' matches=($(sed -s -n -e "/${pattern}/!d" -e "/${arch}/!d" -e "/${group}/!d;F" /etc/audit/rules.d/*.rules))
        # Reset IFS back to default
        unset $IFS
        for match in "${matches[@]}"
        do
                files_to_inspect=("${files_to_inspect[@]}" "${match}")
        done
        # Case when particular rule isn't defined in /etc/audit/rules.d/*.rules yet
        if [ ${#files_to_inspect[@]} -eq "0" ]
        then
                files_to_inspect="/etc/audit/rules.d/$key.rules"
                if [ ! -e "$files_to_inspect" ]
                then
                        touch "$files_to_inspect"
                        chmod 0640 "$files_to_inspect"
                fi
        fi
fi

#
# Indicator that we want to append $full_rule into $audit_file by default
local append_expected_rule=0

for audit_file in "${files_to_inspect[@]}"
do

        # Filter existing $audit_file rules' definitions to select those that:
        # * follow the rule pattern, and
        # * meet the hardware architecture requirement, and
        # * are current syscall group specific
        IFS=$'\n' existing_rules=($(sed -e "/${pattern}/!d" -e "/${arch}/!d" -e "/${group}/!d"  "$audit_file"))
        # Reset IFS back to default
        unset $IFS

        # Process rules found case-by-case
        for rule in "${existing_rules[@]}"
        do
                # Found rule is for same arch & key, but differs (e.g. in count of -S arguments)
                if [ "${rule}" != "${full_rule}" ]
                then
                        # If so, isolate just '(-S \w)+' substring of that rule
                        rule_syscalls=$(echo $rule | grep -o -P '(-S \w+ )+')
                        # Check if list of '-S syscall' arguments of that rule is subset
                        # of '-S syscall' list of expected $full_rule
                        if grep -q -- "$rule_syscalls" <<< "$full_rule"
                        then
                                # Rule is covered (i.e. the list of -S syscalls for this rule is
                                # subset of -S syscalls of $full_rule => existing rule can be deleted
                                # Thus delete the rule from audit.rules & our array
                                sed -i -e "/$rule/d" "$audit_file"
                                existing_rules=("${existing_rules[@]//$rule/}")
                        else
                                # Rule isn't covered by $full_rule - it besides -S syscall arguments
                                # for this group contains also -S syscall arguments for other syscall
                                # group. Example: '-S lchown -S fchmod -S fchownat' => group='chown'
                                # since 'lchown' & 'fchownat' share 'chown' substring
                                # Therefore:
                                # * 1) delete the original rule from audit.rules
                                # (original '-S lchown -S fchmod -S fchownat' rule would be deleted)
                                # * 2) delete the -S syscall arguments for this syscall group, but
                                # keep those not belonging to this syscall group
                                # (original '-S lchown -S fchmod -S fchownat' would become '-S fchmod'
                                # * 3) append the modified (filtered) rule again into audit.rules
                                # if the same rule not already present
                                #
                                # 1) Delete the original rule
                                sed -i -e "/$rule/d" "$audit_file"
                                # 2) Delete syscalls for this group, but keep those from other groups
                                # Convert current rule syscall's string into array splitting by '-S' delimiter
                                IFS=$'-S' read -a rule_syscalls_as_array <<< "$rule_syscalls"
                                # Reset IFS back to default
                                unset $IFS
                                # Declare new empty string to hold '-S syscall' arguments from other groups
                                new_syscalls_for_rule=''
                                # Walk through existing '-S syscall' arguments
                                for syscall_arg in "${rule_syscalls_as_array[@]}"
                                do
                                        # Skip empty $syscall_arg values
                                        if [ "$syscall_arg" == '' ]
                                        then
                                                continue
                                        fi
                                        # If the '-S syscall' doesn't belong to current group add it to the new list
                                        # (together with adding '-S' delimiter back for each of such item found)
                                        if grep -q -v -- "$group" <<< "$syscall_arg"
                                        then
                                                new_syscalls_for_rule="$new_syscalls_for_rule -S $syscall_arg"
                                        fi
                                done
                                # Replace original '-S syscall' list with the new one for this rule
                                updated_rule=${rule//$rule_syscalls/$new_syscalls_for_rule}
                                # Squeeze repeated whitespace characters in rule definition (if any) into one
                                updated_rule=$(echo "$updated_rule" | tr -s '[:space:]')
                                # 3) Append the modified / filtered rule again into audit.rules
                                #    (but only in case it's not present yet to prevent duplicate definitions)
                                if ! grep -q -- "$updated_rule" "$audit_file"
                                then
                                        echo "$updated_rule" >> "$audit_file"
                                fi
                        fi
                else
                        # $audit_file already contains the expected rule form for this
                        # architecture & key => don't insert it second time
                        append_expected_rule=1
                fi
        done

        # We deleted all rules that were subset of the expected one for this arch & key.
        # Also isolated rules containing system calls not from this system calls group.
        # Now append the expected rule if it's not present in $audit_file yet
        if [[ ${append_expected_rule} -eq "0" ]]
        then
                echo "$full_rule" >> "$audit_file"
        fi
done

}

	fix_audit_syscall_rule "auditctl" "$PATTERN" "$GROUP" "$ARCH" "$FULL_RULE"
	fix_audit_syscall_rule "augenrules" "$PATTERN" "$GROUP" "$ARCH" "$FULL_RULE"
done

Record Events that Modify the System's Discretionary Access Controls - chown   [ref]rule

At a minimum, the audit system should collect file permission changes for all users and root. If the auditd daemon is configured to use the augenrules program to read audit rules during daemon startup (the default), add the following line to a file with suffix .rules in the directory /etc/audit/rules.d:

-a always,exit -F arch=b32 -S chown -F auid>=1000 -F auid!=4294967295 -F key=perm_mod
If the system is 64 bit then also add the following line:
-a always,exit -F arch=b64 -S chown -F auid>=1000 -F auid!=4294967295 -F key=perm_mod
If the auditd daemon is configured to use the auditctl utility to read audit rules during daemon startup, add the following line to /etc/audit/audit.rules file:
-a always,exit -F arch=b32 -S chown -F auid>=1000 -F auid!=4294967295 -F key=perm_mod
If the system is 64 bit then also add the following line:
-a always,exit -F arch=b64 -S chown -F auid>=1000 -F auid!=4294967295 -F key=perm_mod

warning  Note that these rules can be configured in a number of ways while still achieving the desired effect. Here the system calls have been placed independent of other system calls. Grouping these system calls with others as identifying earlier in this guide is more efficient.
Rationale:

The changing of file permissions could indicate that a user is attempting to gain access to information that would otherwise be disallowed. Auditing DAC modifications can facilitate the identification of patterns of abuse among both authorized and unauthorized users.

Remediation Shell script:   (show)

Complexity:low
Disruption:low
Strategy:disable


# Perform the remediation for the syscall rule
# Retrieve hardware architecture of the underlying system
[ $(getconf LONG_BIT) = "32" ] && RULE_ARCHS=("b32") || RULE_ARCHS=("b32" "b64")

for ARCH in "${RULE_ARCHS[@]}"
do
	PATTERN="-a always,exit -F arch=${ARCH} -S .* -F auid>=1000 -F auid!=4294967295 -k *"
	GROUP="chown"
	FULL_RULE="-a always,exit -F arch=${ARCH} -S chown -S fchown -S fchownat -S lchown -F auid>=1000 -F auid!=4294967295 -k perm_mod"
	# Perform the remediation for both possible tools: 'auditctl' and 'augenrules'

function fix_audit_syscall_rule {

# Load function arguments into local variables
local tool="$1"
local pattern="$2"
local group="$3"
local arch="$4"
local full_rule="$5"

# Check sanity of the input
if [ $# -ne "5" ]
then
        echo "Usage: fix_audit_syscall_rule 'tool' 'pattern' 'group' 'arch' 'full rule'"
        echo "Aborting."
        exit 1
fi

# Create a list of audit *.rules files that should be inspected for presence and correctness
# of a particular audit rule. The scheme is as follows:
#
# -----------------------------------------------------------------------------------------
#  Tool used to load audit rules | Rule already defined  |  Audit rules file to inspect    |
# -----------------------------------------------------------------------------------------
#        auditctl                |     Doesn't matter    |  /etc/audit/audit.rules         |
# -----------------------------------------------------------------------------------------
#        augenrules              |          Yes          |  /etc/audit/rules.d/*.rules     |
#        augenrules              |          No           |  /etc/audit/rules.d/$key.rules  |
# -----------------------------------------------------------------------------------------
#
declare -a files_to_inspect

# First check sanity of the specified audit tool
i