@angular/service-worker: Request Credential & Cache Policy Stripping

An issue in the @angular/service-worker package compromises the integrity of request-policy enforcement during request reconstruction. When the Angular Service Worker intercepts network requests for matched assets, it reconstructs a new Request object using an internal helper function.

During this reconstruction process, the helper function strips explicit client-defined safety parameters: the credentials configuration (such as credentials: 'omit') and the HTTP cache mode configuration (such as cache: 'no-store'). These are reverted back to standard browser-default parameters (credentials: 'same-origin' and default HTTP cache properties).

This causes the browser to include active credentials (such as cookies or Authorization headers) on outbound requests where the client-side developer explicitly instructed they should be omitted, leading to potential session leaks. Additionally, it causes private or non-cacheable resources to be cached by the service worker's engine, making private page states accessible or persistent inside the client's local cache post-logout.

Impact

Web applications registering the @angular/service-worker package are vulnerable to credential exposure or post-logout cache persistence if client-side code relies on fetch calls with explicit safety attributes (such as { credentials: 'omit' } or { cache: 'no-store' }) targeting paths matched by service worker asset groups.

By stripping these safety boundaries, the service worker exposes same-origin cookies and dynamic sensitive data to endpoints that should not receive them, or retains dynamic user sessions in cache storage where logout operations fail to fully evict user records.

Attack Preconditions

To successfully exploit this vulnerability, all of the following application states and parameters must concurrently exist:

1. Active Angular Service Worker: The target application uses @angular/service-worker and has an active registration of ngsw-worker.js inside the client's browser context.
2. Asset Group Matching: An assetGroups pattern in ngsw-config.json encompasses the target dynamic routing endpoint.
3. Established User Session: The victim user currently has an active authentication state, such as valid same-origin session cookies or auth headers stored by the browser.
4. Client-Side Safe Fetch Call: The application initiates an explicit fetch request to the route with safety parameters: { credentials: 'omit' } or specific cache control parameters (e.g. { cache: 'no-store' }).

Mitigations & Workarounds

If upgrading the @angular/service-worker package is not immediately feasible, developers should implement the following defensive measures:

• Strict Cookie Configuration: Apply strict flags to session cookies (SameSite=Strict; Secure; HttpOnly) and ensure complete route isolation for credential-guarded secure resources.
• Exclude Secure Endpoints from SW Config: Ensure that patterns targeting dynamic, secure endpoints are explicitly excluded from automatic asset groups or caching scopes in your ngsw-config.json.
• Post-Logout Cache Invalidation: Programmatically purge the browser's Cache Storage API entries registered by the Angular Service Worker upon user logout:

  if ('caches' in window) {
    caches.keys().then(names => {
      for (let name of names) {
        if (name.startsWith('ngsw:')) {
          caches.delete(name);
        }
      }
    });
  }
  

Patches

• 22.0.0-rc.2
• 21.2.15
• 20.3.22
• 19.2.23