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 a mode of "0640" or less permissive with the following command:

$ ls -l /etc/ssh/*_key

640 /etc/ssh/ssh_host_dsa_key
640 /etc/ssh/ssh_host_ecdsa_key
640 /etc/ssh/ssh_host_ed25519_key
640 /etc/ssh/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

Restart the SSH daemon for the changes to take effect:

$ sudo systemctl restart sshd.service