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: ```ts 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: ```ts this.http.get('/api/resource', { transferCache: false }); ``` Alternatively, disable the HTTP transfer cache globally in your application bootstrap config: ```ts import { provideClientHydration, withNoHttpTransferCache } from '@angular/platform-browser'; export const appConfig = { providers: [ provideClientHydration( withNoHttpTransferCache() ) ] }; ```

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: ```ts 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: ```ts this.http.get('/api/resource', { transferCache: false }); ``` Alternatively, disable the HTTP transfer cache globally in your application bootstrap config: ```ts import { provideClientHydration, withNoHttpTransferCache } from '@angular/platform-browser'; export const appConfig = { providers: [ provideClientHydration( withNoHttpTransferCache() ) ] }; ```