CVE-2026-68500: Sylius Mollie Plugin vulnerable to payment status forgery via the payment webhook

The shop payment webhook POST /{_locale}/update-payment (route sylius_mollie_shop_payment_webhook) accepts two independent, attacker-controlled parameters: id (the Mollie payment ID, verified against Mollie’s API) and orderId (the Sylius order ID, read directly from the database). The handler never verifies that the Mollie payment belongs to the referenced order.

An unauthenticated attacker who holds any valid paid Mollie payment ID, for example from a EUR 1 order they placed themselves, can submit it together with any victim orderId. The victim’s order payment is then transitioned to completed (or any other Mollie-derived state) without any funds being transferred for that order. Sylius order IDs are sequential integers, and the endpoint requires no authentication, CSRF token or rate limiting, so the attack scales trivially across all pending orders.