Divi Membership <= 2.2.0 - Unauthenticated Privilege Escalation via 'form_id' Parameter

The Divi Membership plugin for WordPress is vulnerable to Privilege Escalation in versions up to, and including, 2.2.0. This is due to the `dmem_form_submit_handler()` function determining the new user's role by iterating all WordPress roles and calling `password_verify()` against an attacker-controlled bcrypt hash supplied in the `form_id` POST parameter, with no validation or whitelist of allowed roles. This makes it possible for unauthenticated attackers to register a new account with the administrator role by submitting a locally computed bcrypt hash of `administrator` as `form_id`, and when `auto_login=on` is submitted, be immediately authenticated as that administrator in the same request, resulting in full site takeover. Exploitation requires a WordPress nonce, but that nonce is publicly emitted on any page rendering the Divi Membership registration form and is therefore obtainable by any unauthenticated visitor.