Disable network management of chrony daemon

An XCCDF Rule

Description

The cmdport option in /etc/chrony.conf can be set to 0 to stop chrony daemon from listening on the UDP port 323 for management connections made by chronyc.

Rationale

Minimizing the exposure of the server functionality of the chrony daemon diminishes the attack surface.

ID: xccdf_org.ssgproject.content_rule_chronyd_no_chronyc_network
Severity: Low
References: CCI-000381

CM-7(1)

FMT_SMF_EXT.1

SRG-OS-000095-GPOS-00049 SRG-OS-000096-GPOS-00050
Updated: about 1 year ago

- name: Disable network management of chrony daemon
  block:

  - name: Check for duplicate values
    lineinfile:
      path: /etc/chrony.conf      create: true
      regexp: ^\s*cmdport\s+
      state: absent
    check_mode: true
    changed_when: false
    register: dupes

  - name: Deduplicate values from /etc/chrony.conf
    lineinfile:
      path: /etc/chrony.conf
      create: true
      regexp: ^\s*cmdport\s+
      state: absent
    when: dupes.found is defined and dupes.found > 1

  - name: Insert correct line to /etc/chrony.conf
    lineinfile:
      path: /etc/chrony.conf
      create: true
      regexp: ^\s*cmdport\s+
      line: cmdport 0
      state: present
  when: ansible_virtualization_type not in ["docker", "lxc", "openvz", "podman", "container"]
  tags:
  - NIST-800-53-CM-7(1)
  - chronyd_no_chronyc_network
  - low_complexity
  - low_disruption
  - low_severity
  - no_reboot_needed
  - restrict_strategy

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

# Strip any search characters in the key arg so that the key can be replaced without
# adding any search characters to the config file.
stripped_key=$(sed 's/[\^=\$,;+]*//g' <<< "^cmdport")
# shellcheck disable=SC2059
printf -v formatted_output "%s %s" "$stripped_key" "0"

# If the key exists, change it. Otherwise, add it to the config_file.
# We search for the key string followed by a word boundary (matched by \>),
# so if we search for 'setting', 'setting2' won't match.
if LC_ALL=C grep -q -m 1 -i -e "^cmdport\\>" "/etc/chrony.conf"; then
    escaped_formatted_output=$(sed -e 's|/|\\/|g' <<< "$formatted_output")
    LC_ALL=C sed -i --follow-symlinks "s/^cmdport\\>.*/$escaped_formatted_output/gi" "/etc/chrony.conf"
else
    if [[ -s "/etc/chrony.conf" ]] && [[ -n "$(tail -c 1 -- "/etc/chrony.conf" || true)" ]]; then
        LC_ALL=C sed -i --follow-symlinks '$a'\\ "/etc/chrony.conf"
    fi
    printf '%s\n' "$formatted_output" >> "/etc/chrony.conf"
fi

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

Disable network management of chrony daemon

Description

Rationale

Remediation - Ansible

Remediation - Shell Script