Eurobank WooCommerce Payment Gateway <= 2.1.1 - Unauthenticated Order Payment Forgery via Unverified Callback

The Eurobank WooCommerce Payment Gateway WordPress plugin through 2.1.1 does not verify that a payment-confirmation request genuinely originates from the payment provider, and ships with the secret that would authenticate it empty by default, allowing unauthenticated attackers to mark any pending order as paid, and to force any order into a failed status without any secret at all.