GHSA-p297-fm68-3q8c

A security bypass vulnerability was discovered in `@angular/common` when Server-Side Rendering (SSR) and hydration are enabled in applications using a hierarchical `HttpClient` configuration with `withRequestsMadeViaParent()`.

The `HttpTransferCache` utility optimizes hydration by caching outgoing HTTP requests performed during SSR and transferring the cached state to the client-side application via `TransferState` (serialized as JSON in `<script id="ng-state">`). Following the remediation of [CVE-2026-50170](https://github.com/angular/angular/security/advisories/GHSA-q6f4-qqrg-jv6x), `HttpTransferCache` automatically skips caching requests that contain authentication headers or credentials (`Authorization`, `Cookie`, `withCredentials`, etc.).

However, when a child `HttpClient` delegates to a parent client via `withRequestsMadeViaParent()`, the child's `TransferCache` interceptor evaluates whether the request is eligible for caching **before** delegating to the parent client's interceptor chain.

If an outgoing request originates as anonymous from the child client, the child `TransferCache` marks the request as cacheable. When the request reaches a parent interceptor that injects sensitive authentication credentials (such as an `Authorization` header or API token), the parent `TransferCache` correctly skips caching the authenticated request. However, when the backend returns the private, authenticated response, the child `TransferCache` still stores the response in `TransferState` based on its initial pre-delegation evaluation.

### Impact

Successful exploitation allows sensitive, user-specific information belonging to an authenticated user to be leaked to unauthenticated or unauthorized users. This occurs when:

1. During SSR, a child `HttpClient` initiates an unauthenticated request that is subsequently authenticated by a parent interceptor. 2. The authenticated response body is cached into the SSR-rendered HTML page (`TransferState`). 3. The rendered HTML page is stored by a shared caching layer (e.g., CDN, edge cache, or reverse proxy) or served across user sessions. 4. Subsequent visitors requesting the same page receive the cached HTML containing the previous user's private data.

### Attack Preconditions & Vulnerable Configurations

An application is affected only if **all** of the following conditions are met:

* **SSR and Hydration Enabled:** The application uses Server-Side Rendering with hydration enabled (e.g., via `provideClientHydration()`). * **Hierarchical `HttpClient` with Delegation:** The application configures a child `HttpClient` using `withRequestsMadeViaParent()`. * **Parent-Level Authentication Injection:** Authentication credentials (such as `Authorization` headers, session cookies, or custom API tokens filtered via `withHttpTransferCacheOptions`) are attached by an interceptor in the **parent** injector chain rather than on the initial child request. * **Shared HTML Caching:** The SSR HTML responses are cached by a shared caching layer (CDN, reverse proxy, or application-level HTML cache).

#### Vulnerable Code Pattern Example

```ts // Parent Injector / Application Config export const appConfig: ApplicationConfig = { providers: [ provideHttpClient( // Parent interceptor attaches sensitive Authorization header withInterceptors([ (req, next) => next(req.clone({ setHeaders: { Authorization: `Bearer ${getToken()}` } })) ]) ), ], };

// Child Injector / Feature or Component Config const childClient = createEnvironmentInjector( [ // Child delegates to parent; TransferCache evaluates req BEFORE parent auth interceptor runs provideHttpClient(withRequestsMadeViaParent()), ], parentInjector ).get(HttpClient);

// Request originates without auth headers -> marked cacheable by child TransferCache childClient.get('/api/user/profile').subscribe(); ```

### Patches

The issue is resolved by updating `@angular/common` to run root interceptors in the terminal request chain so that delegated clients leave inherited root interceptors to the parent chain, preventing duplicate execution and ensuring `HttpTransferCache` evaluates cache eligibility after parent request interceptors run.

* `22.1.1` * `21.2.20` * `20.3.28`

### Workarounds & Mitigations

For applications that cannot immediately upgrade to a patched version, use one of the following mitigations:

1. **Attach Credentials Before or Within the Child Client:** Ensure authentication headers (e.g., `Authorization`) are attached directly when constructing the request or via an interceptor configured directly on the child `HttpClient`, rather than relying solely on parent interceptors. 2. **Apply Explicit Cache Filters on the Child Client:** Configure `withHttpTransferCacheOptions` with a filter on the child client that explicitly excludes endpoints returning user-specific or sensitive data: ```ts provideClientHydration( withHttpTransferCacheOptions({ filter: (req) => !req.url.includes('/api/private/'), }) ) ``` 3. **Disable HTTP Transfer Cache for Sensitive Routes:** If specific SSR routes handle user-authenticated data, disable transfer caching for those requests or ensure the SSR response sets `Cache-Control: no-store` / `private` headers at your edge/CDN layer so personalized HTML is never shared.