Enable SSH Server firewalld Firewall Exception

An XCCDF Rule

Description

If the SSH server is in use, inbound connections to SSH's port should be allowed to permit remote access through SSH. In more restrictive firewalld settings, the SSH port should be added to the proper firewalld zone in order to allow SSH remote access.

To configure firewalld to allow ssh access, run the following command(s):

firewall-cmd --permanent --add-service=ssh

Then run the following command to load the newly created rule(s):

firewall-cmd --reload

warning alert: Warning

The remediation for this rule uses firewall-cmd and nmcli tools. Therefore, it will only be executed if firewalld and NetworkManager services are running. Otherwise, the remediation will be aborted and a informative message will be shown in the remediation report. These respective services will not be started in order to preserve any intentional change in network components related to firewall and network interfaces.

warning alert: Warning

This rule also checks if the SSH port was modified by the administrator in the firewalld services definitions and is reflecting the expected port number. Although this is checked, fixing the custom ssh.xml file placed by the administrator at /etc/firewalld/services it is not in the scope of the remediation since there is no reliable way to manually change the respective file. If the default SSH port is modified, it is on the administrator responsibility to ensure the firewalld customizations in the service port level are properly configured.

Rationale

If inbound SSH connections are expected, adding the SSH port to the proper firewalld zone will allow remote access through the SSH port.

ID: xccdf_org.ssgproject.content_rule_firewalld_sshd_port_enabled
Severity: Medium
References: 3.1.12

1416

AC-17(a) CM-6(b) CM-7(a) CM-7(b)

SRG-OS-000096-GPOS-00050
Updated: 8 months ago

# Remediation is applicable only in certain platforms
if [ ! -f /.dockerenv ] && [ ! -f /run/.containerenv ]; then

if ! rpm -q --quiet "firewalld" ; then
    yum install -y "firewalld"
fiif ! rpm -q --quiet "NetworkManager" ; then
    yum install -y "NetworkManager"
fi
firewalld_sshd_zone='<xccdf-1.2:sub xmlns:xccdf-1.2="http://checklists.nist.gov/xccdf/1.2" idref="xccdf_org.ssgproject.content_value_firewalld_sshd_zone" use="legacy"/>'


if systemctl is-active NetworkManager && systemctl is-active firewalld; then
    # First make sure the SSH service is enabled in run-time for the proper zone.
    # This is to avoid connection issues when new interfaces are addeded to this zone.
    firewall-cmd --zone="$firewalld_sshd_zone" --add-service=ssh

    # This will collect all NetworkManager connections names
    readarray -t nm_connections < <(nmcli -f UUID,TYPE con | grep ethernet | awk '{ print $1 }')
    # If the connection is not yet assigned to a firewalld zone, assign it to the proper zone.
    # This will not change connections which are already assigned to any firewalld zone.
    for connection in "${nm_connections[@]}"; do
        current_zone=$(nmcli -f connection.zone connection show "$connection" | awk '{ print $2}')
        if [ $current_zone = "--" ]; then
            nmcli connection modify "$connection" connection.zone $firewalld_sshd_zone
        fi
    done
    systemctl restart NetworkManager

    # Active zones are zones with at least one interface assigned to it.
    # It is possible that traffic is comming by any active interface and consequently any
    # active zone. So, this make sure all active zones are permanently allowing SSH service.
    readarray -t firewalld_active_zones < <(firewall-cmd --get-active-zones | grep -v interfaces)
    for zone in "${firewalld_active_zones[@]}"; do
        firewall-cmd --permanent --zone="$zone" --add-service=ssh
    done
    firewall-cmd --reload
else
    echo "
    firewalld and NetworkManager services are not active. Remediation aborted!
    This remediation could not be applied because it depends on firewalld and NetworkManager services running.
    The service is not started by this remediation in order to prevent connection issues."
fi

else
    >&2 echo 'Remediation is not applicable, nothing was done'
fi

- name: XCCDF Value firewalld_sshd_zone # promote to variable
  set_fact:
    firewalld_sshd_zone: !!str <xccdf-1.2:sub xmlns:xccdf-1.2="http://checklists.nist.gov/xccdf/1.2" idref="xccdf_org.ssgproject.content_value_firewalld_sshd_zone" use="legacy"/>
  tags:
    - always
- name: Enable SSH Server firewalld Firewall Exception - Ensure firewalld and NetworkManager
    packages are installed
  ansible.builtin.package:
    name: '{{ item }}'
    state: present
  with_items:
  - firewalld
  - NetworkManager
  when: ansible_virtualization_type not in ["docker", "lxc", "openvz", "podman", "container"]
  tags:
  - NIST-800-171-3.1.12
  - NIST-800-53-AC-17(a)
  - NIST-800-53-CM-6(b)
  - NIST-800-53-CM-7(a)
  - NIST-800-53-CM-7(b)
  - configure_strategy
  - firewalld_sshd_port_enabled
  - low_complexity
  - low_disruption
  - medium_severity
  - no_reboot_needed

- name: Enable SSH Server firewalld Firewall Exception - Collect facts about system
    services
  ansible.builtin.service_facts: null
  register: result_services_states
  when: ansible_virtualization_type not in ["docker", "lxc", "openvz", "podman", "container"]
  tags:
  - NIST-800-171-3.1.12
  - NIST-800-53-AC-17(a)
  - NIST-800-53-CM-6(b)
  - NIST-800-53-CM-7(a)
  - NIST-800-53-CM-7(b)
  - configure_strategy
  - firewalld_sshd_port_enabled
  - low_complexity
  - low_disruption
  - medium_severity
  - no_reboot_needed

- name: Enable SSH Server firewalld Firewall Exception - Remediation is applicable
    if firewalld and NetworkManager services are running
  block:

  - name: Enable SSH Server firewalld Firewall Exception - Collect NetworkManager
      connections names
    ansible.builtin.shell:
      cmd: nmcli -f UUID,TYPE con | grep ethernet | awk '{ print $1 }'
    register: result_nmcli_cmd_connections_names
    changed_when: false

  - name: Enable SSH Server firewalld Firewall Exception - Collect NetworkManager
      connections zones
    ansible.builtin.shell:
      cmd: nmcli -f connection.zone connection show {{ item | trim }} | awk '{ print
        $2}'
    register: result_nmcli_cmd_connections_zones
    changed_when: false
    with_items:
    - '{{ result_nmcli_cmd_connections_names.stdout_lines }}'

  - name: Enable SSH Server firewalld Firewall Exception - Ensure NetworkManager connections
      are assigned to a firewalld zone
    ansible.builtin.command:
      cmd: nmcli connection modify {{ item.0 }} connection.zone {{ firewalld_sshd_zone
        }}
    register: result_nmcli_cmd_connections_assignment
    with_together:
    - '{{ result_nmcli_cmd_connections_names.stdout_lines }}'
    - '{{ result_nmcli_cmd_connections_zones.results }}'
    when:
    - item.1.stdout == '--'

  - name: Enable SSH Server firewalld Firewall Exception - Ensure NetworkManager connections
      changes are applied
    ansible.builtin.service:
      name: NetworkManager
      state: restarted
    when:
    - result_nmcli_cmd_connections_assignment is changed

  - name: Enable SSH Server firewalld Firewall Exception - Collect firewalld active
      zones
    ansible.builtin.shell:
      cmd: firewall-cmd --get-active-zones | grep -v interfaces
    register: result_firewall_cmd_zones_names
    changed_when: false

  - name: Enable SSH Server firewalld Firewall Exception - Ensure firewalld zones
      allow SSH
    ansible.builtin.command:
      cmd: firewall-cmd --permanent --zone={{ item }} --add-service=ssh
    register: result_nmcli_cmd_connections_assignment
    changed_when:
    - '''ALREADY_ENABLED'' not in result_nmcli_cmd_connections_assignment.stderr'
    with_items:
    - '{{ result_firewall_cmd_zones_names.stdout_lines }}'

  - name: Enable SSH Server firewalld Firewall Exception - Ensure firewalld changes
      are applied
    ansible.builtin.service:
      name: firewalld
      state: reloaded
    when:
    - result_nmcli_cmd_connections_assignment is changed
  when:
  - ansible_virtualization_type not in ["docker", "lxc", "openvz", "podman", "container"]
  - ansible_facts.services['firewalld.service'].state == 'running'
  - ansible_facts.services['NetworkManager.service'].state == 'running'
  tags:
  - NIST-800-171-3.1.12
  - NIST-800-53-AC-17(a)
  - NIST-800-53-CM-6(b)
  - NIST-800-53-CM-7(a)
  - NIST-800-53-CM-7(b)
  - configure_strategy
  - firewalld_sshd_port_enabled
  - low_complexity
  - low_disruption
  - medium_severity
  - no_reboot_needed

- name: Enable SSH Server firewalld Firewall Exception - Informative message based
    on services states
  ansible.builtin.assert:
    that:
    - ansible_facts.services['firewalld.service'].state == 'running'
    - ansible_facts.services['NetworkManager.service'].state == 'running'
    fail_msg:
    - firewalld and NetworkManager services are not active. Remediation aborted!
    - This remediation could not be applied because it depends on firewalld and NetworkManager
      services running.
    - The service is not started by this remediation in order to prevent connection
      issues.
    success_msg:
    - Enable SSH Server firewalld Firewall Exception remediation successfully executed
  when: ansible_virtualization_type not in ["docker", "lxc", "openvz", "podman", "container"]
  tags:
  - NIST-800-171-3.1.12
  - NIST-800-53-AC-17(a)
  - NIST-800-53-CM-6(b)
  - NIST-800-53-CM-7(a)
  - NIST-800-53-CM-7(b)
  - configure_strategy
  - firewalld_sshd_port_enabled
  - low_complexity
  - low_disruption
  - medium_severity
  - no_reboot_needed

Enable SSH Server firewalld Firewall Exception

Description

Rationale

Remediation - Shell Script

Remediation - Ansible