Disable dnsmasq Service

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Description

The dnsmasq service can be disabled with the following command:

$ sudo systemctl mask --now dnsmasq.service

Rationale

Unless a system is specifically designated to act as a DNS caching, DNS forwarding and/or DHCP server, it is recommended that the package be removed to reduce the potential attack surface.

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='${db:Status-Status}' 'linux-base' 2>/dev/null | grep -q '^installed$'; then

SYSTEMCTL_EXEC='/usr/bin/systemctl'
if [[ $("$SYSTEMCTL_EXEC" is-system-running) != "offline" ]]; then
  "$SYSTEMCTL_EXEC" stop 'dnsmasq.service'
fi
"$SYSTEMCTL_EXEC" disable 'dnsmasq.service'
"$SYSTEMCTL_EXEC" mask 'dnsmasq.service'
# Disable socket activation if we have a unit file for it
if "$SYSTEMCTL_EXEC" -q list-unit-files dnsmasq.socket; then
    if [[ $("$SYSTEMCTL_EXEC" is-system-running) != "offline" ]]; then
      "$SYSTEMCTL_EXEC" stop 'dnsmasq.socket'
    fi
    "$SYSTEMCTL_EXEC" mask 'dnsmasq.socket'
fi
# The service may not be running because it has been started and failed,
# so let's reset the state so OVAL checks pass.
# Service should be 'inactive', not 'failed' after reboot though.
"$SYSTEMCTL_EXEC" reset-failed 'dnsmasq.service' || true

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:
  - disable_strategy
  - low_complexity
  - low_disruption
  - medium_severity
  - no_reboot_needed
  - service_dnsmasq_disabled

- name: Disable dnsmasq Service - Disable service dnsmasq
  block:

  - name: Disable dnsmasq Service - Collect systemd Services Present in the System
    ansible.builtin.command: systemctl -q list-unit-files --type service
    register: service_exists
    changed_when: false
    failed_when: service_exists.rc not in [0, 1]
    check_mode: false

  - name: Disable dnsmasq Service - Ensure dnsmasq.service is Masked
    ansible.builtin.systemd:
      name: dnsmasq.service
      state: stopped
      enabled: false
      masked: true
    when: service_exists.stdout_lines is search("dnsmasq.service", multiline=True)

  - name: Unit Socket Exists - dnsmasq.socket
    ansible.builtin.command: systemctl -q list-unit-files dnsmasq.socket
    register: socket_file_exists
    changed_when: false
    failed_when: socket_file_exists.rc not in [0, 1]
    check_mode: false

  - name: Disable dnsmasq Service - Disable Socket dnsmasq
    ansible.builtin.systemd:
      name: dnsmasq.socket
      enabled: false
      state: stopped
      masked: true
    when: socket_file_exists.stdout_lines is search("dnsmasq.socket", multiline=True)
  tags:
  - disable_strategy
  - low_complexity
  - low_disruption
  - medium_severity
  - no_reboot_needed
  - service_dnsmasq_disabled
  - special_service_block
  when: '"linux-base" in ansible_facts.packages'