Angular SSR has a Server-Side Request Forgery (SSRF) flaw

### Impact The vulnerability is a **Server-Side Request Forgery (SSRF)** flaw within the URL resolution mechanism of Angular's Server-Side Rendering package (`@angular/ssr`). The function `createRequestUrl` uses the native `URL` constructor. When an incoming request path (e.g., `originalUrl` or `url`) begins with a **double forward slash (`//`) or backslash (`\\`)**, the `URL` constructor treats it as a **schema-relative URL**. This behavior overrides the security-intended base URL (protocol, host, and port) supplied as the second argument, instead resolving the URL against the scheme of the base URL but adopting the attacker-controlled hostname. This allows an attacker to specify an external domain in the URL path, tricking the Angular SSR environment into setting the page's virtual location (accessible via `DOCUMENT` or `PlatformLocation` tokens) to this attacker-controlled domain. Any subsequent **relative HTTP requests** made during the SSR process (e.g., using `HttpClient.get('assets/data.json')`) will be incorrectly resolved against the attacker's domain, forcing the server to communicate with an arbitrary external endpoint. #### Exploit Scenario A request to `http://localhost:4200//attacker-domain.com/some-page` causes Angular to believe the host is attacker-domain.com. A relative request to api/data then becomes a server-side request to `http://attacker-domain.com/api/data`. ### Patches - `@angular/ssr` 19.2.18 - `@angular/ssr` 20.3.6 - `@angular/ssr` 21.0.0-next.8 ## Mitigation The application's internal location must be robustly determined from the incoming request. The fix requires sanitizing or validating the request path to prevent it from being interpreted as a schema-relative URL (i.e., ensuring it does not start with `//`). #### Server-Side Middleware If you can't upgrade to a patched version, implement a **middleware** on the Node.js/Express server that hosts the Angular SSR application to explicitly reject or sanitize requests where the path begins with a double slash (`//`). **Example (Express/Node.js):** ```ts // Place this middleware before the Angular SSR handler app.use((req, res, next) => { if (req.originalUrl?.startsWith('//')) { // Sanitize by forcing a single slash req.originalUrl = req.originalUrl.replace(/^\/\/+/, '/'); req.url = req.url.replace(/^\/\/+/, '/'); } next(); }); ``` ### References - Report: https://github.com/angular/angular-cli/issues/31464 - Fix: https://github.com/angular/angular-cli/pull/31474

Source published

16 Oct 2025 21:28:19 UTC

Source modified

16 Oct 2025 21:55:01 UTC

Observed here

24 Oct 2026 13:17:17 UTC

Source terms

GitHub Advisory Database · CC-BY-4.0

Original source record · Cite this exact observation · Complete original publisher JSON

This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: osv · GitHub Advisory Database · CC-BY-4.0. Source text is retained; field grouping and change labels are provided by ChangeIntel.

CVSS_V4 · CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N

Publisher rating · HIGH