Vulnerability Discussion

GSSAPI authentication is used to provide additional authentication mechanisms to applications. Allowing GSSAPI authentication through SSH exposes the system's GSSAPI to remote hosts, increasing the attack surface of the system.

Check

Verify that OL 9 SSH daemon does not allow GSSAPI authentication with the following command:

$ sudo /usr/sbin/sshd -dd 2>&1 | awk '/filename/ {print $4}' | tr -d '\r' | tr '\n' ' ' | xargs sudo grep -iH '^\s*gssapiauthentication'
GSSAPIAuthentication no

If the value is returned as "yes", the returned line is commented out, no output is returned, and the use of GSSAPI authentication has not been documented with the information system security officer (ISSO), this is a finding.

Fix

Configure the SSH daemon to not allow GSSAPI authentication.

Add or uncomment the following line to "/etc/ssh/sshd_config" or to a file in "/etc/ssh/sshd_config.d" and set the value to "no":

GSSAPIAuthentication no

The SSH service must be restarted for changes to take effect:

$ sudo systemctl restart sshd.service