Verify Permissions on SSH Server Public *.pub Key Files

Classification:

compliance

Framework:

Control:

Description

To properly set the permissions of /etc/ssh/*.pub, run the command:

$ sudo chmod 0644 /etc/ssh/*.pub

Rationale

If a public host key file is modified by an unauthorized user, the SSH service may be compromised.

Remediation

Shell script

The following script can be run on the host to remediate the issue.

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

find -H /etc/ssh/ -maxdepth 1 -perm /u+xs,g+xws,o+xwt -type f -regex '^.\*\.pub$' -exec chmod u-xs,g-xws,o-xwt {} \;

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)
 command: find -H /etc/ssh/ -maxdepth 1 -perm /u+xs,g+xws,o+xwt -type f -regex "^.\*\.pub$"
 register: files\_found
 changed\_when: false
 failed\_when: false
 check\_mode: false
 when: ansible\_virtualization\_type not in ["docker", "lxc", "openvz", "podman", "container"]
 tags:
 - NIST-800-171-3.1.13
 - NIST-800-171-3.13.10
 - NIST-800-53-AC-17(a)
 - NIST-800-53-AC-6(1)
 - NIST-800-53-CM-6(a)
 - PCI-DSS-Req-2.2.4
 - PCI-DSSv4-2.2.6
 - configure\_strategy
 - file\_permissions\_sshd\_pub\_key
 - low\_complexity
 - low\_disruption
 - medium\_severity
 - no\_reboot\_needed

- name: Set permissions for /etc/ssh/ file(s)
 file:
 path: '{{ item }}'
 mode: u-xs,g-xws,o-xwt
 state: file
 with\_items:
 - '{{ files\_found.stdout\_lines }}'
 when: ansible\_virtualization\_type not in ["docker", "lxc", "openvz", "podman", "container"]
 tags:
 - NIST-800-171-3.1.13
 - NIST-800-171-3.13.10
 - NIST-800-53-AC-17(a)
 - NIST-800-53-AC-6(1)
 - NIST-800-53-CM-6(a)
 - PCI-DSS-Req-2.2.4
 - PCI-DSSv4-2.2.6
 - configure\_strategy
 - file\_permissions\_sshd\_pub\_key
 - low\_complexity
 - low\_disruption
 - medium\_severity
 - no\_reboot\_needed