Integrate PhonePe with WooCommerce <= 1.2.1 - Unauthenticated Payment Bypass via Transaction ID Reuse

The Integrate PhonePe with WooCommerce WordPress plugin through 1.2.1 does not validate that a verified payment transaction belongs to the order being marked as paid, nor does it verify the authenticity of its payment-completion request, allowing unauthenticated attackers to reuse a single valid transaction to mark arbitrary orders as paid and bypass payment.