My software application runs on port 5700. In the past few days with the recent Windows updates, some of my users' software has stopped working due to this port now being in use by the System process (PID: 4).
I am not sure how to determine which program is using this port? Either it's being used by Windows itself (which would be odd, for the System process to just start using a new port), or some other program is using the System process as some sort of proxy.
For example, I've seen that when I listen to some ports for HTTP requests in my app, then the PID that is shown using that port number is 4 (System process). This is more or less confirmed here: https://github.com/dotnet/corefx/issues/428
I have tried running the command
netsh http show urlacl to see all of the HTTP port reservations, but my port doesn't show up in this list. So it doesn't appear to be reserved, but it's in use.
The exception in question when we try listening on that port is:
A TCP error (10013: An attempt was made to access a socket in a way forbidden by its access permissions) occurred while listening on IP Endpoint=0.0.0.0:5700.