MasterStudy LMS <= 3.3.1 - Unauthenticated Privilege Escalation via stm_lms_register AJAX Action

The MasterStudy LMS plugin for WordPress is vulnerable to Privilege Escalation in all versions up to, and including, 3.3.1. This is due to insufficient validation checks within the _register_user() function called by the 'wp_ajax_nopriv_stm_lms_register' AJAX action. This makes it possible for unauthenticated attackers to register a user with administrator-level privileges when MasterStudy LMS Pro is installed and the LMS Forms Editor add-on is enabled.