Nginx UI is a web user interface for the Nginx web server. In 2.3.4 and earlier, an authenticated user can perform Server-Side Request Forgery (SSRF) by creating a cluster node pointing to an arbitrary internal URL and then sending API requests with the X-Node-ID header. The Proxy middleware forwards these requests to the attacker-specified internal address, bypassing network segmentation and enabling access to services bound to localhost or internal networks.