Vulnerability Discussion

Configuring this setting for the SSH daemon provides additional assurance that remote logon via SSH will require a password, even in the event of misconfiguration elsewhere.

Check

Verify the SSH daemon does not allow authentication using known host’s authentication with the following command:

$ sudo grep -ir IgnoreUserKnownHosts /etc/ssh/sshd_config*

IgnoreUserKnownHosts yes

If the value is returned as "no", the returned line is commented out, or no output is returned, this is a finding.
If conflicting results are returned, this is a finding.

Fix

Configure the SSH daemon to not allow authentication using known host’s authentication.

Add the following line in "/etc/ssh/sshd_config", or uncomment the line and set the value to "yes":

IgnoreUserKnownHosts yes

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