BitPay Gateway for WooCommerce <= 4.1.3 - Unauthenticated Payment Bypass via Payment Return Handler

The BitPay Gateway for WooCommerce WordPress plugin through 4.1.3 does not bind the payment provider's transaction confirmation to the order it completes, nor verify the confirmed amount, allowing an unauthenticated attacker who holds a single genuine low-value transaction to mark arbitrary higher-value orders as paid.