Vulnerability Discussion

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

Check

Verify the SSH private host key files have mode "0640" or less permissive with the following command:

$ sudo ls -l /etc/ssh/ssh_host*key

-rw------- 1 root ssh_keys 668 Nov 28 06:43 ssh_host_dsa_key
-rw------- 1 root ssh_keys 582 Nov 28 06:43 ssh_host_key
-rw------- 1 root ssh_keys 887 Nov 28 06:43 ssh_host_rsa_key

If any private host key file has a mode more permissive than "0640", this is a finding.

Fix

Configure the mode of SSH private host key files under "/etc/ssh" to "0640" with the following command:

$ sudo chmod 0640 /etc/ssh/ssh_host*key

The SSH daemon must be restarted for the changes to take effect. To restart the SSH daemon, run the following command:

$ sudo systemctl restart sshd.service