RHEL 9 must not allow blank or null passwords.

If an account has an empty password, anyone could log in and run commands with the privileges of that account. Accounts with empty passwords should never be used in operational environments.

Verify that null passwords cannot be used with the following command:

$ sudo grep -i nullok /etc/pam.d/system-auth /etc/pam.d/password-auth

If output is produced, this is a finding.

If the system administrator (SA) can demonstrate that the required configuration is contained in a PAM configuration file included or substacked from the system-auth file, this is not a finding.

If PAM is managed with authselect, use the following command to remove instances of "nullok":

$ sudo authselect enable-feature without-nullok

Otherwise, remove any instances of the "nullok" option in the "/etc/pam.d/password-auth" and "/etc/pam.d/system-auth" files to prevent logons with empty passwords.

Note: Manual changes to the listed file may be overwritten by the "authselect" program.