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 -alL /etc/ssh/ssh_host*key
-rw-r----- 1 root wheel 668 Nov 28 06:43 ssh_host_dsa_key
-rw-r----- 1 root wheel 582 Nov 28 06:43 ssh_host_key
-rw-r----- 1 root wheel 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