Vulnerability Discussion

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

Check

Verify the SSH public host key files have a mode of "0644" or less permissive with the following command:

Note: SSH public key files may be found in other directories on the system depending on the installation.

$ sudo stat -c "%a %n" /etc/ssh/*.pub

644 /etc/ssh/ssh_host_dsa_key.pub
644 /etc/ssh/ssh_host_ecdsa_key.pub
644 /etc/ssh/ssh_host_ed25519_key.pub
644 /etc/ssh/ssh_host_rsa_key.pub

If any key.pub file has a mode more permissive than "0644", this is a finding.

Fix

Change the mode of public host key files under "/etc/ssh" to "0644" with the following command:

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

Restart the SSH daemon for the changes to take effect:

$ sudo systemctl restart sshd.service