Angular: Cache-Key Ambiguity in HttpTransferCache Leading to Cross-Request Response Reuse and State Poisoning

Overview

Angular's HttpTransferCache caches HTTP requests made during Server-Side Rendering (SSR) so that they can be reused during client-side hydration.

During SSR, HttpTransferCache previously generated identical key material for distinct request parameters when repeated values were present because repeated values were joined with commas:

new HttpParams().set('role', 'user,admin')
new HttpParams().append('role', 'user').append('role', 'admin')

Both requests previously serialized as role=user,admin, allowing distinct HttpClient requests to produce the same transfer-cache key material.

Impact

In an SSR application, this cache-key ambiguity can make a later security-sensitive HttpClient request receive the response from an earlier semantically different request in the same render. For example, an attacker-influenced scalar-comma request can be cached and then replayed as the response for a trusted repeated-param authorization or data request to the same URL. As a result, Angular's server-rendered output can be based on the wrong backend response because the trusted request is not dispatched. This can lead to:

• State Poisoning: Using incorrect or attacker-influenced cached responses for subsequent application logic.
• Cross-Request Response Reuse: Reusing cached responses across requests with semantically different parameters.

Patched Versions

• 22.0.2
• 21.2.19
• 20.3.27

Workarounds

If you cannot upgrade immediately, configure your HttpClient requests to skip transfer caching for sensitive endpoints where repeated parameter keys are used:

this.http.get('/api/resource', {
  transferCache: false
});

Alternatively, disable the HTTP transfer cache globally in your application bootstrap config:

import { provideClientHydration, withNoHttpTransferCache } from '@angular/platform-browser';

export const appConfig = {
  providers: [
    provideClientHydration(
      withNoHttpTransferCache()
    )
  ]
};

Affected packages

• @angular/common >= 22.0.0-next.0, < 22.0.2
• @angular/common >= 21.0.0-next.0, < 21.2.19
• @angular/common >= 20.0.0-next.0, < 20.3.27
• @angular/common <= 19.2.25

Remediation

Upgrade to a patched release:

• @angular/common 22.0.2
• @angular/common 21.2.19
• @angular/common 20.3.27