Stripe Payment Forms by WP Full Pay <= 8.4.3 - Missing Authorization to Unauthenticated Payment Record Manipulation via 'paymentIntentId' Parameter

The WP Full Stripe Free plugin for WordPress is vulnerable to Missing Authorization in versions up to, and including, 8.4.3 via the wpfs_update_failed_payment_status AJAX action. The handler is registered through both wp_ajax_ and wp_ajax_nopriv_ hooks and the underlying update_failed_payment_status() function performs no capability check, no nonce verification, and no logged-in check before calling $this->db->updatePaymentByEventId() with attacker-controlled POST parameters. This makes it possible for unauthenticated attackers who can obtain a valid Stripe Payment Intent ID for the target site (Payment Intent IDs are exposed to the customer browser during normal Stripe.js checkout flows) to manipulate payment records in the site's database, marking previously successful payments as failed and overwriting failure codes and messages with attacker-supplied values.