Vulnerability Discussion

Configuring these settings for the SSH daemon provides additional assurance that remote logon via SSH will not use unused methods of authentication, even in the event of misconfiguration elsewhere.

Check

Verify the SSH daemon does not allow authentication using unused methods of authentication with the following command:

$ sudo grep -i "KerberosAuthentication\|GSSAPIAuthentication" /etc/ssh/sshd_config

KerberosAuthentication no
GSSAPIAuthentication no

If the values are returned as "yes", the returned line is commented out, no output is returned, or has not been documented with the ISSO, this is a finding.

Fix

Configure the SSH daemon to not allow authentication using unused methods of authentication.

Add the following line in "/etc/ssh/sshd_config", or uncomment the line and set the value to "no":

KerberosAuthentication no
GSSAPIAuthentication no

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