To verify that null passwords cannot be used, run the following command:
# grep nullok /etc/pam.d/system-auth
If this produces any output, it may be possible to log into accounts with empty passwords. If NULL passwords can be used, this is a finding.
Fix Text (F-43444r4_fix)
If an account is configured for password authentication but does not have an assigned password, it may be possible to log onto the account without authentication. Remove any instances of the "nullok" option in "/etc/pam.d/system-auth" to prevent logons with empty passwords.