The Angular CLI is a command-line interface tool for Angular applications. The vulnerability is a Server-Side Request Forgery (SSRF) flaw within the URL resolution mechanism of Angulars Server-Side Rendering package (@angular/ssr) before 19.2.18, 20.3.6, and 21.0.0-next.8. 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 pages 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 attackers domain, forcing the server to communicate with an arbitrary external endpoint. This vulnerability is fixed in 19.2.18, 20.3.6, and 21.0.0-next.8.
The web server receives a URL or similar request from an upstream component and retrieves the contents of this URL, but it does not sufficiently ensure that the request is being sent to the expected destination.