Verify Ownership on SSH Server Private *_key Key Files

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Description

SSH server private keys, files that match the /etc/ssh/*_key glob, must be owned by root user.

Rationale

If an unauthorized user obtains the private SSH host key file, the host could be impersonated.

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 ]; then

find /etc/ssh/ -maxdepth 1 -type f ! -uid 0 -regex '^.*_key$' -exec chown 0 {} \;

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: Find /etc/ssh/ file(s) matching ^.*_key$
  command: find -H /etc/ssh/ -maxdepth 1 -type f ! -uid 0 -regex "^.*_key$"
  register: files_found
  changed_when: false
  failed_when: false
  check_mode: false
  when: ansible_virtualization_type not in ["docker", "lxc", "openvz", "podman", "container"]
  tags:
  - CCE-86117-9
  - configure_strategy
  - file_ownership_sshd_private_key
  - low_complexity
  - low_disruption
  - medium_severity
  - no_reboot_needed

- name: Ensure owner on /etc/ssh/ file(s) matching ^.*_key$
  file:
    path: '{{ item }}'
    owner: '0'
    state: file
  with_items:
  - '{{ files_found.stdout_lines }}'
  when: ansible_virtualization_type not in ["docker", "lxc", "openvz", "podman", "container"]
  tags:
  - CCE-86117-9
  - configure_strategy
  - file_ownership_sshd_private_key
  - low_complexity
  - low_disruption
  - medium_severity
  - no_reboot_needed