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:

$ sshd -T | grep ignoreuserknownhosts

ignoreuserknownhosts yes

If the value is returned as "no", this is a finding.

Fix

Configure the SSH daemon to not allow known hosts authentication.

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

IgnoreUserKnownHosts yes

Alternatively, add the setting to an include file if the line "Include /etc/ssh/sshd_config.d/*.conf" is found at the top of the "/etc/ssh/sshd_config" file:

$ echo 'IgnoreUserKnownHosts yes' > /etc/ssh/sshd_config.d/40-knownhosts.conf

Restart the SSH daemon for the settings to take effect:

$ systemctl restart sshd.service