Order Tracking < 3.6.0 - Unauthenticated Payment Confirmation Forgery via PayPal IPN Listener

Description

The plugin does not verify that a PayPal payment notification was sent to the merchant's account, or that its amount matches the order total, before marking an order as paid, which could allow unauthenticated attackers to mark arbitrary orders as paid using a trivial payment to their own PayPal account.