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.