Verify Group Who Owns /var/log/messages File

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Description

To properly set the group owner of /var/log/messages, run the command:

$ sudo chgrp adm /var/log/messages

or

$ sudo chgrp root /var/log/messages

Rationale

The /var/log/messages file contains logs of error messages in the system and should only be accessed by authorized personnel.

Remediation

Shell script

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

#!/bin/bash

newgroup=""
if getent group "adm" >/dev/null 2>&1; then
  newgroup="adm"
elif getent group "root" >/dev/null 2>&1; then
  newgroup="root"
fi

if [[ -z "${newgroup}" ]]; then
  >&2 echo "adm and root is not a defined group on the system"
else
if ! stat -c "%g %G" "/var/log/messages" | grep -E -w -q "adm|root"; then
    chgrp --no-dereference "$newgroup" /var/log/messages
fi

fi

Ansible playbook

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

- name: Check that the adm group is defined
  ansible.builtin.getent:
    database: group
    key: adm
  ignore_errors: true
  when: file_groupowner_var_log_messages_newgroup is undefined
  tags:
  - configure_strategy
  - file_groupowner_var_log_messages
  - low_complexity
  - low_disruption
  - medium_severity
  - no_reboot_needed

- name: Set the file_groupowner_var_log_messages_newgroup variable if adm found
  ansible.builtin.set_fact:
    file_groupowner_var_log_messages_newgroup: adm
  when: ansible_facts.getent_group["adm"] is defined
  tags:
  - configure_strategy
  - file_groupowner_var_log_messages
  - low_complexity
  - low_disruption
  - medium_severity
  - no_reboot_needed

- name: Check that the root group is defined
  ansible.builtin.getent:
    database: group
    key: root
  ignore_errors: true
  when: file_groupowner_var_log_messages_newgroup is undefined
  tags:
  - configure_strategy
  - file_groupowner_var_log_messages
  - low_complexity
  - low_disruption
  - medium_severity
  - no_reboot_needed

- name: Set the file_groupowner_var_log_messages_newgroup variable if root found
  ansible.builtin.set_fact:
    file_groupowner_var_log_messages_newgroup: root
  when: ansible_facts.getent_group["root"] is defined
  tags:
  - configure_strategy
  - file_groupowner_var_log_messages
  - low_complexity
  - low_disruption
  - medium_severity
  - no_reboot_needed

- name: Test for existence /var/log/messages
  ansible.builtin.stat:
    path: /var/log/messages
  register: file_exists
  tags:
  - configure_strategy
  - file_groupowner_var_log_messages
  - low_complexity
  - low_disruption
  - medium_severity
  - no_reboot_needed

- name: Ensure group owner on /var/log/messages
  ansible.builtin.file:
    path: /var/log/messages
    follow: false
    group: '{{ file_groupowner_var_log_messages_newgroup }}'
  when: file_exists.stat is defined and file_exists.stat.exists
  tags:
  - configure_strategy
  - file_groupowner_var_log_messages
  - low_complexity
  - low_disruption
  - medium_severity
  - no_reboot_needed