Sylius Mollie Plugin vulnerable to payment status forgery via the payment webhook

Impact

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.

Patches

Fixed in versions 2.2.8, 3.2.4 and 3.3.1. The webhook now binds the payment to the order: it reads the Mollie payment ID stored server-side for that order when the payment was created and compares it to the incoming Mollie payment ID. On mismatch the request is acknowledged with HTTP 200 and no state change is applied. HTTP 200 is intentional, because Mollie retries the webhook on any non-2xx response.

The stored ID lives in one of two places depending on the checkout flow, and the fix reads both of them (mirroring CaptureAction):

• payment.getDetails()['payment_mollie_id'] for the standard Shop API and Apple Pay Direct flows, stored in CreatePaymentAction.
• order.getMolliePaymentId() for the QR-code flow, which stores the ID on the order itself (QrCodeAction).

Reading only the payment details would reject legitimate QR-code payments, because their payment details carry no payment_mollie_id, so both sources must be consulted.

Workarounds

If you cannot upgrade immediately, patch the vulnerability at the project level by decorating the plugin's webhook controller. The decorator checks that the incoming Mollie id matches the id stored for that order before handing over to the original controller, so no plugin behaviour (state machine, logging) is lost and no extra Mollie API call is made. Works on both 2.2 and 3.x.

Step 1. Create the decorator

Create src/Controller/Mollie/SecurePaymentWebhookController.php in your Sylius project:

<?php

declare(strict_types=1);

namespace App\Controller\Mollie;

use Sylius\Component\Core\Model\OrderInterface;
use Sylius\Component\Order\Repository\OrderRepositoryInterface;
use Sylius\MolliePlugin\Controller\Shop\PaymentWebhookController;
use Symfony\Component\HttpFoundation\JsonResponse;
use Symfony\Component\HttpFoundation\Request;
use Symfony\Component\HttpFoundation\Response;

final class SecurePaymentWebhookController
{
    public function __construct(
        private readonly PaymentWebhookController $inner,
        private readonly OrderRepositoryInterface $orderRepository,
    ) {
    }

    public function __invoke(Request $request): Response
    {
        $orderId = $request->get('orderId');
        $molliePaymentId = $request->get('id');

        if (null === $orderId || null === $molliePaymentId) {
            return ($this->inner)($request);
        }

        /** @var OrderInterface|null $order */
        $order = $this->orderRepository->findOneBy(['id' => $orderId]);
        if (null === $order) {
            return ($this->inner)($request);
        }

        $storedMollieId = $this->resolveStoredMollieId($order);

        // Reject any webhook whose Mollie id does not match the one stored for this order.
        // 200 is intentional: Mollie retries on any non-2xx response.
        if (null === $storedMollieId || $storedMollieId !== (string) $molliePaymentId) {
            return new JsonResponse(null, Response::HTTP_OK);
        }

        return ($this->inner)($request);
    }

    private function resolveStoredMollieId(OrderInterface $order): ?string
    {
        $payment = $order->getLastPayment();
        $fromDetails = $payment?->getDetails()['payment_mollie_id'] ?? null;
        if (null !== $fromDetails && '' !== $fromDetails) {
            return (string) $fromDetails;
        }

        // QR-code flow stores the Mollie id on the order itself.
        if (method_exists($order, 'getMolliePaymentId')) {
            $fromOrder = $order->getMolliePaymentId();
            if (null !== $fromOrder && '' !== $fromOrder) {
                return (string) $fromOrder;
            }
        }

        return null;
    }
}

Step 2. Register the decorator

Append to your project's config/services.yaml:

services:
    App\Controller\Mollie\SecurePaymentWebhookController:
        decorates: sylius_mollie.controller.shop.payment_webhook
        public: true
        arguments:
            $inner: '@.inner'
            $orderRepository: '@sylius.repository.order'

decorates: keeps the original service ID, so the route _controller: sylius_mollie.controller.shop.payment_webhook keeps working with no route changes. @.inner is the original plugin controller.

Step 3. Clear the cache

bin/console cache:clear