Nexi XPay Build <= 7.6.2 - Unauthenticated Payment Bypass via NPG Notification Handler

The Nexi XPay Build WordPress plugin through 7.6.2 does not correctly validate the security token on its payment notification route, accepting the request when the target order has no stored token, which allows unauthenticated attackers to mark arbitrary orders as paid, or to mark genuinely paid orders as failed.