Paid Member Subscriptions < 3.1.0 - Unauthenticated Subscription Activation via Stripe SCA Resume AJAX Endpoint

Description

The plugin is vulnerable to Authentication Bypass due to missing server-side token validation on the Stripe SCA resume AJAX endpoint, allowing any request that supplied a valid payment intent ID to drive the handler against arbitrary member subscriptions. This makes it possible for unauthenticated attackers to complete another member's Stripe SCA authentication flow using only a known payment intent ID, activating or altering a subscription without authorization.