VaulTLS is a modern solution for managing mTLS (mutual TLS) certificates. Prior to 0.9.1, user accounts created through the User web UI have an empty but not NULL password set, attackers can use this to login with an empty password. This is combined with that fact, that previously disabling the password based login only effected the frontend, but still allowed login via the API. This vulnerability is fixed in 0.9.1.