CCAvenue Payment Gateway for WooCommerce <= 3.1 - Unauthenticated Order Payment Completion via Webhook Forgery

The CCAvenue Payment Gateway for WooCommerce WordPress plugin through 3.1 does not verify that a payment-confirmation request genuinely originates from the payment provider, and derives its verification key from a value that is empty on a default install, allowing unauthenticated attackers to forge a confirmation and mark any WooCommerce order as paid without payment.