CVE-2026-88059

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 pag