Quick PayPal Payments <= 5.7.50 - Unauthenticated Payment Bypass via PayPal IPN

The Quick Paypal Payments WordPress plugin through 5.7.50 does not verify the paid amount, receiver, or payment status in its PayPal IPN handler and marks an order paid on an order-token match alone, so a buyer who pays an arbitrary small amount can have a full-price order marked paid.