User Frontend: AI Powered Frontend Posting, User Directory, Profile, Membership & User Registration <= 4.3.1 - Unauthenticated Insecure Direct Object Reference to Arbitrary User Subscription Overwrite

The User Frontend: AI Powered Frontend Posting, User Directory, Profile, Membership & User Registration plugin for WordPress is vulnerable to Insecure Direct Object Reference in all versions up to, and including, 4.3.1 via the payment_page() function due to missing validation on the 'user_id' user controlled key. This makes it possible for unauthenticated attackers to activate a free subscription pack for any user on the site, overwriting their existing paid subscription and causing loss of paid features.