CVE-2026-31889: Shopware App Registration Flow Credential Takeover

Shopware is an open-source commerce platform that supports extensibility through external applications. These applications communicate with the Shopware instance via an API, utilizing a defined registration flow to establish trust. During this handshake, the platform exchanges cryptographic secrets to authenticate future requests, including webhooks and token generation. The security of this integration relies heavily on the integrity of the registration and re-registration mechanisms.

CVE-2026-31889 identifies a critical authentication bypass vulnerability (CWE-290) in the app re-registration flow of Shopware core and platform packages. Versions prior to 6.6.10.15 and 6.7.8.1 implement a legacy HMAC-based handshake that fails to adequately verify the identity of the requesting shop during a re-registration event. The protocol relies exclusively on a shared App Secret, which is identical across all installations of a specific public app.

Because the system lacks a requirement to prove possession of the unique Shop Secret, unauthorized entities can successfully spoof re-registration requests. This architectural flaw exposes the communication channel to hijacking. Attackers can modify the shop-url metadata stored on the app server, redirecting all subsequent backend communication to an arbitrary, attacker-controlled domain.

The root cause of CVE-2026-31889 lies in the incomplete cryptographic validation during the Shopware app re-registration process. When a Shopware instance initially registers with an external app server, it uses a shared App Secret, defined in the app's manifest file, to authenticate the request. The app server then generates and returns a unique Shop Secret, which is securely stored by the Shopware instance and used to sign subsequent communication.

During a re-registration event, which is typically triggered when a shop's domain changes, the Shopware instance sends a request to update its metadata on the app server. In vulnerable versions, this re-registration request is authenticated using only the original, shared App Secret. The protocol does not mandate the inclusion of a signature generated with the unique Shop Secret previously assigned to the specific shop.

This design choice fails to enforce a continuous chain of trust. For public Shopware apps, the App Secret is widely distributed and easily extractable from the app manifest or installation package. Consequently, any actor possessing the App Secret can craft a valid re-registration request. The app server, receiving a correctly signed request using the App Secret, processes the metadata update without verifying that the requester actually controls the shop instance in question.

The vulnerability was resolved by introducing a dual-signature requirement and a formalized secret rotation mechanism. Previously, the re-registration endpoint only verified the HMAC signature derived from the App Secret. The patched implementation requires the request to carry signatures from both the shared App Secret and the unique Shop Secret, ensuring that only the legitimate owner of the established trust relationship can modify the registration state.

The core patch introduces the AppSecretRotationService, which handles the atomic rotation of integration secrets. This service implements a formal confirmation flow to prevent state desynchronization between the shop and the app server. A new secret is generated and staged locally, followed by a handshake initiation with the external app server. The old secret is only invalidated after the app server explicitly confirms receipt of the new secret.

Additionally, the patch addresses edge cases related to app uninstallation. The introduction of the deleted_apps table and the DeletedAppsGateway ensures that the unique Shop Secret is preserved even if the app is temporarily removed. This architectural change prevents attackers from exploiting a race condition where an uninstalled app leaves the shop vulnerable to unauthorized re-registration using only the public App Secret.

// Vulnerable Implementation Concept (Pseudocode)
public function handleReRegistration(Request $request, string $appSecret) {
    $signature = $request->header('shopware-app-signature');
    if (!hash_equals(hash_hmac('sha256', $request->getContent(), $appSecret), $signature)) {
        throw new UnauthorizedException();
    }
    // Updates shop URL without verifying the existing Shop Secret
    $this->shopRepository->updateUrl($request->get('shop_id'), $request->get('shop_url'));
}

// Patched Implementation Concept (Pseudocode)
public function handleReRegistration(Request $request, string $appSecret, string $existingShopSecret) {
    $appSignature = $request->header('shopware-app-signature');
    $shopSignature = $request->header('shopware-shop-signature');
 
    // Requires dual validation
    $validAppSig = hash_equals(hash_hmac('sha256', $request->getContent(), $appSecret), $appSignature);
    $validShopSig = hash_equals(hash_hmac('sha256', $request->getContent(), $existingShopSecret), $shopSignature);
 
    if (!$validAppSig || !$validShopSig) {
        throw new UnauthorizedException();
    }
    $this->shopRepository->updateUrl($request->get('shop_id'), $request->get('shop_url'));
}

Exploitation of CVE-2026-31889 requires the attacker to possess the shared App Secret for the targeted application. For publicly available extensions in the Shopware ecosystem, this secret is generally embedded within the app manifest and can be extracted by downloading the application package. No prior authentication to the target Shopware instance or the external app server is required.

The attacker initiates the exploit by identifying the target Shop ID associated with a specific Shopware installation. With the App Secret and Shop ID in hand, the attacker crafts an HTTP POST request simulating a re-registration event. The payload contains the target Shop ID and a modified shop-url parameter pointing to an attacker-controlled endpoint.

The forged request is signed using the extracted App Secret and transmitted to the application's backend registration server. The vulnerable app server validates the HMAC signature, confirms it matches the App Secret, and updates its internal routing database. The attacker's infrastructure is now registered as the authoritative endpoint for the target shop.

The successful exploitation of CVE-2026-31889 results in a complete compromise of the communication channel between the external application and the Shopware instance. By altering the shop-url mapping on the app server, the attacker forces the external system to route all subsequent traffic to a malicious domain. This traffic includes highly sensitive integration data.

The primary consequence is the interception of API credentials and integration tokens generated by the app server. When the external application attempts to authenticate with the Shopware instance, it transmits these credentials to the attacker-controlled URL. The attacker can then utilize these intercepted tokens to impersonate the application and interact directly with the Shopware API.

Depending on the specific permissions granted to the compromised application, the attacker may achieve extensive control over the Shopware environment. This can include reading customer data, modifying product listings, or executing administrative actions. The CVSS v3.1 score of 8.9 reflects the high severity of this vulnerability, given the low attack complexity and the severe confidentiality and integrity impact.

Administrators must immediately update the shopware/core and shopware/platform packages to version 6.6.10.15 or 6.7.8.1. These releases contain the necessary architectural changes, including the dual-signature validation and the AppSecretRotationService. Upgrading the core platform is the primary defense against this vulnerability.

Following the core update, administrators must trigger a secret rotation for all currently installed applications. This forces the generation of new, cryptographically secure Shop Secrets and establishes the new validation baseline. The rotation process is initiated via an authenticated POST request to the /api/_action/app-system/secret/rotate Admin API endpoint.

Application developers who maintain external app servers for Shopware integrations must also update their backend infrastructure. Custom implementations must be modified to parse and validate the new shopware-shop-signature header during re-registration events. Failure to update the external app server logic will leave the integration vulnerable, even if the Shopware instance has been patched.