RHEL 9 must not allow a noncertificate trusted host SSH logon to the system.

SSH trust relationships mean a compromise on one host can allow an attacker to move trivially to other hosts.

Verify the operating system does not allow a noncertificate trusted host SSH logon to the system 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*hostbasedauthentication'

HostbasedAuthentication no

If the "HostbasedAuthentication" keyword is not set to "no", is missing, or is commented out, this is a finding.

If the required value is not set, this is a finding.

To configure RHEL 9 to not allow a noncertificate trusted host SSH logon to the system, add or modify the following line in "/etc/ssh/sshd_config" or in a file in "/etc/ssh/sshd_config.d".

HostbasedAuthentication no

Restart the SSH daemon for the settings to take effect:

$ sudo systemctl restart sshd.service