CVE-2026-53638: Sylius: Channel-based payment method restriction bypass on shop account orders API endpoint

An authorization bypass vulnerability exists in the shop account API. The PATCH /api/v2/shop/account/orders/{tokenValue}/payments/{paymentId} endpoint, used by an authenticated shop customer to change the payment method of an order that has been placed but not yet paid (state STATE_NEW), does not validate that the chosen payment method is enabled for the order’s channel. The equivalent checkout endpoint (PATCH /api/v2/shop/orders/{tokenValue}/payments/{paymentId}) correctly rejects out-of-channel payment methods with HTTP 422; the account endpoint silently accepts them and returns HTTP 200.

An authenticated customer can therefore assign any globally enabled payment method to their own placed order, including methods that the store operator has explicitly excluded from that channel.