Verify Group Who Owns /var/log/lastlog File

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Description

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

$ sudo chgrp utmp /var/log/lastlog

or

$ sudo chgrp root /var/log/lastlog

Rationale

The /var/log/lastlog file contains logs of reports the most recent login of all users 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

if getent group "utmp" >/dev/null 2>&1; then
  newgroup="utmp"
elif getent group "root" >/dev/null 2>&1; then
  newgroup="root"
fi
if [[ -z ${newgroup} ]]; then
  echo "utmp and root is not a defined group on the system"
  exit 1
fi

find -L /var/log/ -maxdepth 1 -type f  ! -group utmp ! -group root -regextype posix-extended -regex '.*lastlog(\.[^\/]+)?' -exec chgrp -L $newgroup {} \;

Ansible playbook

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

- name: Check that the utmp group is defined
  getent:
    database: group
    key: utmp
  ignore_errors: true
  when: file_groupowner_var_log_lastlog_newgroup is undefined
  tags:
  - configure_strategy
  - file_groupowner_var_log_lastlog
  - low_complexity
  - low_disruption
  - medium_severity
  - no_reboot_needed

- name: Set the file_groupowner_var_log_lastlog_newgroup variable if utmp found
  set_fact:
    file_groupowner_var_log_lastlog_newgroup: utmp
  when: ansible_facts.getent_group["utmp"] is defined
  tags:
  - configure_strategy
  - file_groupowner_var_log_lastlog
  - low_complexity
  - low_disruption
  - medium_severity
  - no_reboot_needed

- name: Check that the root group is defined
  getent:
    database: group
    key: root
  ignore_errors: true
  when: file_groupowner_var_log_lastlog_newgroup is undefined
  tags:
  - configure_strategy
  - file_groupowner_var_log_lastlog
  - low_complexity
  - low_disruption
  - medium_severity
  - no_reboot_needed

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

- name: Find /var/log/ file(s) matching .*lastlog(\.[^\/]+)?
  command: find -L /var/log/ -maxdepth 1 -type f  ! -group utmp ! -group root -regextype
    posix-extended -regex ".*lastlog(\.[^\/]+)?"
  register: files_found
  changed_when: false
  failed_when: false
  check_mode: false
  tags:
  - configure_strategy
  - file_groupowner_var_log_lastlog
  - low_complexity
  - low_disruption
  - medium_severity
  - no_reboot_needed

- name: Ensure group owner on /var/log/ file(s) matching .*lastlog(\.[^\/]+)?
  file:
    path: '{{ item }}'
    group: '{{ file_groupowner_var_log_lastlog_newgroup }}'
    state: file
  with_items:
  - '{{ files_found.stdout_lines }}'
  tags:
  - configure_strategy
  - file_groupowner_var_log_lastlog
  - low_complexity
  - low_disruption
  - medium_severity
  - no_reboot_needed