Verify nftables Service is Disabled

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Description

nftables is a subsystem of the Linux kernel providing filtering and classification of network packets/datagrams/frames and is the successor to iptables. The nftables service can be disabled with the following command:

systemctl disable nftables

Rationale

Running both firewalld and nftables may lead to conflict. nftables is actually one of the backends for firewalld management tools.

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 ( [ ! -f /.dockerenv ] && [ ! -f /run/.containerenv ] && dpkg-query --show --showformat='${db:Status-Status}\n' 'firewalld' 2>/dev/null | grep -q installed && dpkg-query --show --showformat='${db:Status-Status}\n' 'nftables' 2>/dev/null | grep -q installed ); then

SYSTEMCTL_EXEC='/usr/bin/systemctl'
"$SYSTEMCTL_EXEC" stop 'nftables.service'
"$SYSTEMCTL_EXEC" disable 'nftables.service'
"$SYSTEMCTL_EXEC" mask 'nftables.service'
# Disable socket activation if we have a unit file for it
if "$SYSTEMCTL_EXEC" -q list-unit-files nftables.socket; then
    "$SYSTEMCTL_EXEC" stop 'nftables.socket'
    "$SYSTEMCTL_EXEC" mask 'nftables.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 'nftables.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:
  - PCI-DSSv4-1.2.1
  - disable_strategy
  - low_complexity
  - low_disruption
  - medium_severity
  - no_reboot_needed
  - service_nftables_disabled

- name: Verify nftables Service is Disabled - 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
  when: ( ansible_virtualization_type not in ["docker", "lxc", "openvz", "podman",
    "container"] and "firewalld" in ansible_facts.packages and "nftables" in ansible_facts.packages
    )
  tags:
  - PCI-DSSv4-1.2.1
  - disable_strategy
  - low_complexity
  - low_disruption
  - medium_severity
  - no_reboot_needed
  - service_nftables_disabled

- name: Verify nftables Service is Disabled - Ensure nftables.service is Masked
  ansible.builtin.systemd:
    name: nftables.service
    state: stopped
    enabled: false
    masked: true
  when:
  - ( ansible_virtualization_type not in ["docker", "lxc", "openvz", "podman", "container"]
    and "firewalld" in ansible_facts.packages and "nftables" in ansible_facts.packages
    )
  - service_exists.stdout_lines is search("nftables.service", multiline=True)
  tags:
  - PCI-DSSv4-1.2.1
  - disable_strategy
  - low_complexity
  - low_disruption
  - medium_severity
  - no_reboot_needed
  - service_nftables_disabled

- name: Unit Socket Exists - nftables.socket
  ansible.builtin.command: systemctl -q list-unit-files nftables.socket
  register: socket_file_exists
  changed_when: false
  failed_when: socket_file_exists.rc not in [0, 1]
  check_mode: false
  when: ( ansible_virtualization_type not in ["docker", "lxc", "openvz", "podman",
    "container"] and "firewalld" in ansible_facts.packages and "nftables" in ansible_facts.packages
    )
  tags:
  - PCI-DSSv4-1.2.1
  - disable_strategy
  - low_complexity
  - low_disruption
  - medium_severity
  - no_reboot_needed
  - service_nftables_disabled

- name: Verify nftables Service is Disabled - Disable Socket nftables
  ansible.builtin.systemd:
    name: nftables.socket
    enabled: false
    state: stopped
    masked: true
  when:
  - ( ansible_virtualization_type not in ["docker", "lxc", "openvz", "podman", "container"]
    and "firewalld" in ansible_facts.packages and "nftables" in ansible_facts.packages
    )
  - socket_file_exists.stdout_lines is search("nftables.socket", multiline=True)
  tags:
  - PCI-DSSv4-1.2.1
  - disable_strategy
  - low_complexity
  - low_disruption
  - medium_severity
  - no_reboot_needed
  - service_nftables_disabled