The SSH server service, sshd, is commonly needed.
However, if it can be disabled, do so.
This is unusual, as SSH is a common method for encrypted and authenticated
remote access.
include disable_sshd
class disable_sshd {
service {'sshd':
enable => false,
ensure => 'stopped',
}
}
Remediation - OS Build Blueprint
[customizations.services]
masked = ["sshd"]
Remediation - Ansible
- name: Gather the package facts
package_facts:
manager: auto
tags:
- NIST-800-53-CM-3(6)
- NIST-800-53-IA-2(4)
- disable_strategy
- high_severity
- low_complexity
- low_disruption
- no_reboot_needed
- service_sshd_disabled
- name: Disable SSH Server If Possible - 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: '"kernel" in ansible_facts.packages'
tags:
- NIST-800-53-CM-3(6)
- NIST-800-53-IA-2(4)
- disable_strategy
- high_severity
- low_complexity
- low_disruption
- no_reboot_needed
- service_sshd_disabled
- name: Disable SSH Server If Possible - Ensure sshd.service is Masked
ansible.builtin.systemd:
name: sshd.service
state: stopped
enabled: false
masked: true
when:
- '"kernel" in ansible_facts.packages'
- service_exists.stdout_lines is search("sshd.service", multiline=True)
tags:
- NIST-800-53-CM-3(6)
- NIST-800-53-IA-2(4)
- disable_strategy
- high_severity
- low_complexity
- low_disruption
- no_reboot_needed
- service_sshd_disabled
- name: Unit Socket Exists - sshd.socket
ansible.builtin.command: systemctl -q list-unit-files sshd.socket
register: socket_file_exists
changed_when: false
failed_when: socket_file_exists.rc not in [0, 1]
check_mode: false
when: '"kernel" in ansible_facts.packages'
tags:
- NIST-800-53-CM-3(6)
- NIST-800-53-IA-2(4)
- disable_strategy
- high_severity
- low_complexity
- low_disruption
- no_reboot_needed
- service_sshd_disabled
- name: Disable SSH Server If Possible - Disable Socket sshd
ansible.builtin.systemd:
name: sshd.socket
enabled: false
state: stopped
masked: true
when:
- '"kernel" in ansible_facts.packages'
- socket_file_exists.stdout_lines is search("sshd.socket", multiline=True)
tags:
- NIST-800-53-CM-3(6)
- NIST-800-53-IA-2(4)
- disable_strategy
- high_severity
- low_complexity
- low_disruption
- no_reboot_needed
- service_sshd_disabled
Remediation - Shell Script
# Remediation is applicable only in certain platforms
if rpm --quiet -q kernel; then
SYSTEMCTL_EXEC='/usr/bin/systemctl'
"$SYSTEMCTL_EXEC" stop 'sshd.service'
"$SYSTEMCTL_EXEC" disable 'sshd.service'
"$SYSTEMCTL_EXEC" mask 'sshd.service'
# Disable socket activation if we have a unit file for it
if "$SYSTEMCTL_EXEC" -q list-unit-files sshd.socket; then
"$SYSTEMCTL_EXEC" stop 'sshd.socket'
"$SYSTEMCTL_EXEC" mask 'sshd.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 'sshd.service' || true
else
>&2 echo 'Remediation is not applicable, nothing was done'
fi