User Profile Builder <= 4.0.3 - Unauthenticated Privilege Escalation to 'role' Parameter via Legacy Meta-Name Collision on [wppb-register]

The User Profile Builder – Beautiful User Registration Forms, User Profiles & User Role Editor plugin for WordPress is vulnerable to Privilege Escalation in all versions up to, and including, 4.0.3 via the role parameter handled by the wppb_add_meta_to_user_on_activation() function. The vulnerability exists because the activation handler passes the attacker-supplied role value directly to WP_User::set_role() with no allow-list validation, and the 4.0.3 reserved-name check exempts pre-existing form fields from the block, allowing a legacy field with meta-name role to persist and bridge attacker-controlled request input into the serialized signup record stored in wp_signups. This makes it possible for unauthenticated attackers to gain a fully activated WordPress administrator account by submitting role=administrator through the public [wppb-register] shortcode form and subsequently clicking the confirmation activation link. Exploitation requires the site to have a legacy form field with meta-name role carried over from before the 4.0.3 upgrade, email confirmation enabled, and open user registration — all stable site-state conditions once established.