SimpleForm <= 3.10.0 - Unauthenticated Privilege Escalation to wp_capabilities Mass Assignment via simpleform_wp_register

The SimpleForm – Form Maker to Chat Apps with Quiz, Poll and Multi Lead Notifications plugin for WordPress is vulnerable to Privilege Escalation in all versions up to, and including, 3.10.0 This is due to the `wp_ajax_nopriv_simpleform_wp_register` AJAX action lacking any capability check for role assignment and the `save_custom_fields_to_user_meta()` function using an exclusion list that omits `wp_capabilities`, combined with `get_form_settings()` returning a hard-coded defaults array that unconditionally enables meta writing regardless of the supplied `form_id`. This makes it possible for unauthenticated attackers to create a new Administrator-level WordPress account by supplying `wp_capabilities[administrator]=1` alongside standard registration fields. The nonce required by the endpoint is publicly emitted into the `front_end_data` JavaScript object on every front-end page via `wp_enqueue_scripts`, making it trivially obtainable by any unauthenticated visitor before submitting the malicious request.

Severity vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H