Vulnerability Discussion

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

Check

Verify the SSH daemon does not allow known hosts authentication with the following command:

$ sudo grep -ir ignoreuser /etc/ssh/sshd_config /etc/ssh/sshd_config.d/*

IgnoreUserKnownHosts yes

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

Fix

Configure the SSH daemon to not allow known hosts authentication.

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

IgnoreUserKnownHosts yes

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

$ sudo systemctl restart sshd.service