Super Forms – Drag & Drop Form Builder <= 6.3.316 - Authenticated (Subscriber+) Privilege Escalation via 'user_id' Parameter in Register & Login

The Super Forms – Drag & Drop Form Builder plugin for WordPress is vulnerable to Privilege Escalation in all versions up to, and including, 6.3.316. This is due to the Register & Login add-on's before_email_success_msg() function, in its register_login_action='update' flow, trusting an attacker-supplied user_id value and passing it to wp_update_user() without any ownership or capability check. Because the super_save_form AJAX action also enforces no capability check, any authenticated user with Subscriber-level access and above can create the required malicious form (register_login_action='update' with register_login_user_id_update='true') and then submit it with user_id set to an administrator's ID along with a new user_pass/user_email. This makes it possible for authenticated attackers with Subscriber-level access and above to overwrite the credentials of arbitrary existing accounts — including administrators — resulting in account takeover and full site compromise.