On any CI or Selenium host this is noVNC — a browser-viewable live view into a container's desktop.
The official Selenium Docker images publish 7900 for noVNC, so you can watch a test run by opening http://localhost:7900/?autoconnect=1&resize=scale&password=secret. It is an HTTP endpoint that proxies the container's VNC server into a web page. IANA registers 7900 as mevent, Multicast Event, but that assignment carries no implementation you are likely to meet. If 7900 is open on a build agent or a Kubernetes node, look for selenium/standalone- or selenium/node- containers.
Do not expose
The documented default password is literally "secret", and access grants full interactive control of a real browser session — including whatever it is logged into. Keep it on localhost or a private network.
$ curl -sI http://127.0.0.1:7900/Seen this on your network? Beige Box scans your Wi-Fi and shows every open port on every device — and its Ports tool links straight back here.
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Corrections or a missing port? Reply @rimrocksystems.