Ubuntu OS must not allow accounts configured with blank or null passwords.

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

Verify null passwords cannot be used. Run the following command:

     $ grep nullok /etc/pam.d/common-auth /etc/pam.d/common-password

If this produces any output, this is a finding.

Remove any instances of the "nullok" option in "/etc/pam.d/common-password" to prevent logons with empty passwords.

Remove any instances of the "nullok" option in "/etc/pam.d/common-auth" and "/etc/pam.d/common-password".