Disable telnet Service

An XCCDF Rule

Description

Make sure that the activation of the telnet service on system boot is disabled. The telnet socket can be disabled with the following command:

$ sudo systemctl mask --now telnet.socket

warning alert: Warning

If the system relies on xinetd to manage telnet sessions, ensure the telnet service is disabled by the following line: disable = yes. Note that the xinetd file for telnet is not created automatically, therefore it might have different names.

Rationale

The telnet protocol uses unencrypted network communication, which means that data from the login session, including passwords and all other information transmitted during the session, can be stolen by eavesdroppers on the network. The telnet protocol is also subject to man-in-the-middle attacks.

ID: xccdf_org.ssgproject.content_rule_service_telnet_disabled
Severity: High
References: 1 11 12 14 15 16 3 5 8 9

APO13.01 BAI10.01 BAI10.02 BAI10.03 BAI10.05 DSS01.04 DSS05.02 DSS05.03 DSS05.04 DSS05.05 DSS05.07 DSS05.10 DSS06.03 DSS06.06 DSS06.10

3.1.13 3.4.7

164.308(a)(4)(i) 164.308(b)(1) 164.308(b)(3) 164.310(b) 164.312(e)(1) 164.312(e)(2)(ii)

4.3.3.2.2 4.3.3.5.1 4.3.3.5.2 4.3.3.5.3 4.3.3.5.4 4.3.3.5.5 4.3.3.5.6 4.3.3.5.7 4.3.3.5.8 4.3.3.6.1 4.3.3.6.2 4.3.3.6.3 4.3.3.6.4 4.3.3.6.5 4.3.3.6.6 4.3.3.6.7 4.3.3.6.8 4.3.3.6.9 4.3.3.7.1 4.3.3.7.2 4.3.3.7.3 4.3.3.7.4 4.3.4.3.2 4.3.4.3.3

SR 1.1 SR 1.10 SR 1.11 SR 1.12 SR 1.13 SR 1.2 SR 1.3 SR 1.4 SR 1.5 SR 1.6 SR 1.7 SR 1.8 SR 1.9 SR 2.1 SR 2.2 SR 2.3 SR 2.4 SR 2.5 SR 2.6 SR 2.7 SR 3.1 SR 3.5 SR 3.8 SR 4.1 SR 4.3 SR 5.1 SR 5.2 SR 5.3 SR 7.1 SR 7.6

A.11.2.6 A.12.1.2 A.12.5.1 A.12.6.2 A.13.1.1 A.13.2.1 A.14.1.3 A.14.2.2 A.14.2.3 A.14.2.4 A.18.1.4 A.6.2.1 A.6.2.2 A.7.1.1 A.9.1.2 A.9.2.1 A.9.2.2 A.9.2.3 A.9.2.4 A.9.2.6 A.9.3.1 A.9.4.2 A.9.4.3

CM-6(a) CM-7(a) CM-7(b) IA-5(1)(c)

PR.AC-1 PR.AC-3 PR.AC-6 PR.AC-7 PR.IP-1 PR.PT-3 PR.PT-4
Updated: about 1 year ago


[customizations.services]
disabled = ["telnet"]

- name: Gather the package facts
  package_facts:
    manager: auto
  tags:
  - NIST-800-171-3.1.13
  - NIST-800-171-3.4.7  - NIST-800-53-CM-6(a)
  - NIST-800-53-CM-7(a)
  - NIST-800-53-CM-7(b)
  - NIST-800-53-IA-5(1)(c)
  - disable_strategy
  - high_severity
  - low_complexity
  - low_disruption
  - no_reboot_needed
  - service_telnet_disabled

- name: Block Disable service telnet
  block:

  - name: Disable service telnet
    block:

    - name: Disable service telnet
      systemd:
        name: telnet.service
        enabled: 'no'
        state: stopped
        masked: 'yes'
    rescue:

    - name: Intentionally ignored previous 'Disable service telnet' failure, service
        was already disabled
      meta: noop
  when: ( ansible_virtualization_type not in ["docker", "lxc", "openvz", "podman",
    "container"] and "telnet-server" in ansible_facts.packages )
  tags:
  - NIST-800-171-3.1.13
  - NIST-800-171-3.4.7
  - NIST-800-53-CM-6(a)
  - NIST-800-53-CM-7(a)
  - NIST-800-53-CM-7(b)
  - NIST-800-53-IA-5(1)(c)
  - disable_strategy
  - high_severity
  - low_complexity
  - low_disruption
  - no_reboot_needed
  - service_telnet_disabled

- name: Unit Socket Exists - telnet.socket
  command: systemctl -q list-unit-files telnet.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 "telnet-server" in ansible_facts.packages )
  tags:
  - NIST-800-171-3.1.13
  - NIST-800-171-3.4.7
  - NIST-800-53-CM-6(a)
  - NIST-800-53-CM-7(a)
  - NIST-800-53-CM-7(b)
  - NIST-800-53-IA-5(1)(c)
  - disable_strategy
  - high_severity
  - low_complexity
  - low_disruption
  - no_reboot_needed
  - service_telnet_disabled

- name: Disable socket telnet
  systemd:
    name: telnet.socket
    enabled: 'no'
    state: stopped
    masked: 'yes'
  when:
  - ( ansible_virtualization_type not in ["docker", "lxc", "openvz", "podman", "container"]
    and "telnet-server" in ansible_facts.packages )
  - socket_file_exists.stdout_lines is search("telnet.socket",multiline=True)
  tags:
  - NIST-800-171-3.1.13
  - NIST-800-171-3.4.7
  - NIST-800-53-CM-6(a)
  - NIST-800-53-CM-7(a)
  - NIST-800-53-CM-7(b)
  - NIST-800-53-IA-5(1)(c)
  - disable_strategy
  - high_severity
  - low_complexity
  - low_disruption
  - no_reboot_needed
  - service_telnet_disabled

# Remediation is applicable only in certain platforms
if ( [ ! -f /.dockerenv ] && [ ! -f /run/.containerenv ] && rpm --quiet -q telnet-server ); then

SYSTEMCTL_EXEC='/usr/bin/systemctl'
"$SYSTEMCTL_EXEC" stop 'telnet.service'
"$SYSTEMCTL_EXEC" disable 'telnet.service'"$SYSTEMCTL_EXEC" mask 'telnet.service'
# Disable socket activation if we have a unit file for it
if "$SYSTEMCTL_EXEC" -q list-unit-files telnet.socket; then
    "$SYSTEMCTL_EXEC" stop 'telnet.socket'
    "$SYSTEMCTL_EXEC" mask 'telnet.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 'telnet.service' || true

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

include disable_telnet

class disable_telnet {
  service {'telnet':
    enable => false,
    ensure => 'stopped',  }
}

Disable telnet Service

Description

Rationale

Remediation - OS Build Blueprint

Remediation - Ansible

Remediation - Shell Script

Remediation - Puppet