InstantCMS is a free and open source content management system. A blind Server-Side Request Forgery (SSRF) vulnerability in InstantCMS up to and including 2.17.3 allows authenticated remote attackers to make nay HTTP/HTTPS request via the package parameter. It is possible to make any HTTP/HTTPS request to any website in installer functionality. Due to such vulnerability it is possible to for example scan local network, call local services and its functions, conduct a DoS attack, and/or disclose a servers real IP if its behind a reverse proxy. It is also possible to exhaust server resources by sending plethora of such requests. As of time of publication, no patched releases are available.
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.