A vulnerability was discovered in "@angular/common" when Server-Side Rendering (SSR) and hydration are enabled. 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". However, the caching mechanism fails to inspect the "withCredentials" flag or the "Cookie" header of outgoing requests. As a result, credentialed, user-specific responses may be cached by default in the shared "TransferState" payload. When these responses are serialized into the HTML, any caching layer (such as a CDN, reverse proxy, or shared server cache) that caches the SSR-rendered HTML page could inadvertently cache and leak one user's private data to other users, leading to a high-severity information disclosure vulnerability. Impact Successful exploitation allows an unauthenticated attacker to obtain sensitive, user-specific information of other authenticated users. This occurs when: * The SSR-rendered HTML containing the cached private data is stored in a shared cache (e.g., CDN, reverse proxy). * Subsequent requests for the same page receive the cached HTML containing the first user's private data. Attack Preconditions * SSR and Hydration Enabled: The Angular application must be configured to use Server-Side Rendering and hydration (e.g., using "provideClientHydration()"). * Credentialed Requests during SSR: The application must perform HTTP requests that require user-specific authentication (using cookies or "withCredentials: true") during the initial server-side render. * Shared Caching: The application's HTML responses must be cached by a shared caching layer (CDN, reverse proxy, or server-side cache) without proper cache-control headers to distinguish authenticated users. Patches - 22.0.0-rc.2 - 21.2.15 - 20.3.22 - 19.2.23