Verify /boot/grub/grub.cfg User Ownership

Description

The file /boot/grub/grub.cfg should be owned by the root user to prevent destruction or modification of the file. To properly set the owner of /boot/grub/grub.cfg, run the command:

$ sudo chown root /boot/grub/grub.cfg

Rationale

Only root should be able to 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 ( dpkg-query --show --showformat='${db:Status-Status}\n' 'grub2-common' 2>/dev/null | grep -q '^installed' && dpkg-query --show --showformat='${db:Status-Status}
' 'linux-base' 2>/dev/null | grep -q ^installed ) && [ ! -d /sys/firmware/efi ] && { ! ( [ -f /.dockerenv ] || [ -f /run/.containerenv ] ); }; then

chown 0 /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:
  - CJIS-5.5.2.2
  - NIST-800-171-3.4.5
  - NIST-800-53-AC-6(1)
  - NIST-800-53-CM-6(a)
  - PCI-DSS-Req-7.1
  - PCI-DSSv4-2.2
  - PCI-DSSv4-2.2.6
  - configure_strategy
  - file_owner_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 and "linux-base" in ansible_facts.packages
    )
  - not ( ansible_virtualization_type in ["docker", "lxc", "openvz", "podman", "container"]
    )
  tags:
  - CJIS-5.5.2.2
  - NIST-800-171-3.4.5
  - NIST-800-53-AC-6(1)
  - NIST-800-53-CM-6(a)
  - PCI-DSS-Req-7.1
  - PCI-DSSv4-2.2
  - PCI-DSSv4-2.2.6
  - configure_strategy
  - file_owner_grub2_cfg
  - low_complexity
  - low_disruption
  - medium_severity
  - no_reboot_needed

- name: Ensure owner 0 on /boot/grub/grub.cfg
  file:
    path: /boot/grub/grub.cfg
    owner: '0'
  when:
  - '"/boot/efi" not in ansible_mounts | map(attribute="mount") | list'
  - ( "grub2-common" in ansible_facts.packages and "linux-base" in ansible_facts.packages
    )
  - not ( ansible_virtualization_type in ["docker", "lxc", "openvz", "podman", "container"]
    )
  - file_exists.stat is defined and file_exists.stat.exists
  tags:
  - CJIS-5.5.2.2
  - NIST-800-171-3.4.5
  - NIST-800-53-AC-6(1)
  - NIST-800-53-CM-6(a)
  - PCI-DSS-Req-7.1
  - PCI-DSSv4-2.2
  - PCI-DSSv4-2.2.6
  - configure_strategy
  - file_owner_grub2_cfg
  - low_complexity
  - low_disruption
  - medium_severity
  - no_reboot_needed