Vulnerability Discussion

Open X displays allow an attacker to capture keystrokes and execute commands remotely.

Check

Verify remote X connections for interactive users are encrypted.

Check that remote X connections are encrypted with the following command:

# grep -i x11forwarding /etc/ssh/sshd_config | grep -v "^#"

X11Forwarding yes

If the "X11Forwarding" keyword is set to "no" or is missing, this is a finding.

Fix

Configure SSH to encrypt connections for interactive users.

Edit the "/etc/ssh/sshd_config" file to uncomment or add the line for the "X11Forwarding" keyword and set its value to "yes" (this file may be named differently or be in a different location if using a version of SSH that is provided by a third-party vendor):

X11Forwarding yes

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

# systemctl restart sshd