Verify /boot/grub/grub.cfg Permissions

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Description

File permissions for /boot/grub/grub.cfg should be set to 600. To properly set the permissions of /boot/grub/grub.cfg, run the command:

$ sudo chmod 600 /boot/grub/grub.cfg

Rationale

Proper permissions ensure that only the root user can modify important boot parameters.

Remediation

Shell script

The following script can be run on the host to remediate the issue.

#!/bin/bash

# Remediation is applicable only in certain platforms
if [ ! -d /sys/firmware/efi ] && dpkg-query --show --showformat='${db:Status-Status}\n' 'grub2-common' 2>/dev/null | grep -q installed && { [ ! -f /.dockerenv ] && [ ! -f /run/.containerenv ]; }; then

chmod u-xs,g-xwrs,o-xwrt /boot/grub/grub.cfg

else
    >&2 echo 'Remediation is not applicable, nothing was done'
fi

Ansible playbook

The following playbook can be run with Ansible to remediate the issue.

- name: Gather the package facts
  package_facts:
    manager: auto
  tags:
  - NIST-800-171-3.4.5
  - NIST-800-53-AC-6(1)
  - NIST-800-53-CM-6(a)
  - PCI-DSSv4-2.2
  - PCI-DSSv4-2.2.6
  - configure_strategy
  - file_permissions_grub2_cfg
  - low_complexity
  - low_disruption
  - medium_severity
  - no_reboot_needed

- name: Test for existence /boot/grub/grub.cfg
  stat:
    path: /boot/grub/grub.cfg
  register: file_exists
  when:
  - '"/boot/efi" not in ansible_mounts | map(attribute="mount") | list'
  - '"grub2-common" in ansible_facts.packages'
  - ansible_virtualization_type not in ["docker", "lxc", "openvz", "podman", "container"]
  tags:
  - NIST-800-171-3.4.5
  - NIST-800-53-AC-6(1)
  - NIST-800-53-CM-6(a)
  - PCI-DSSv4-2.2
  - PCI-DSSv4-2.2.6
  - configure_strategy
  - file_permissions_grub2_cfg
  - low_complexity
  - low_disruption
  - medium_severity
  - no_reboot_needed

- name: Ensure permission u-xs,g-xwrs,o-xwrt on /boot/grub/grub.cfg
  file:
    path: /boot/grub/grub.cfg
    mode: u-xs,g-xwrs,o-xwrt
  when:
  - '"/boot/efi" not in ansible_mounts | map(attribute="mount") | list'
  - '"grub2-common" in ansible_facts.packages'
  - ansible_virtualization_type not in ["docker", "lxc", "openvz", "podman", "container"]
  - file_exists.stat is defined and file_exists.stat.exists
  tags:
  - NIST-800-171-3.4.5
  - NIST-800-53-AC-6(1)
  - NIST-800-53-CM-6(a)
  - PCI-DSSv4-2.2
  - PCI-DSSv4-2.2.6
  - configure_strategy
  - file_permissions_grub2_cfg
  - low_complexity
  - low_disruption
  - medium_severity
  - no_reboot_needed