VNC – How to Set Up VNC Connection via SSH Proxy Machine

Have a look at reptyr, which does exactly that. The github page has all the information.

reptyr - A tool for "re-ptying" programs.

reptyr is a utility for taking an existing running program and attaching it to a new terminal. Started a long-running process over ssh, but have to leave and don't want to interrupt it? Just start a screen, use reptyr to grab it, and then kill the ssh session and head on home.

USAGE

reptyr PID

"reptyr PID" will grab the process with id PID and attach it to your current terminal.

After attaching, the process will take input from and write output to the new terminal, including ^C and ^Z. (Unfortunately, if you background it, you will still have to run "bg" or "fg" in the old terminal. This is likely impossible to fix in a reasonable way without patching your shell.)

Assuming your linux box is accessible from the internet at 1.2.3.4 on port 23008, on an external system I would do:

external% ssh -p 23008 -L 13389:192.168.8.y:3389 username@1.2.3.4

I'd then connect to the port-forwarded RDP system with

external% rdesktop localhost:13389

If your external box isn't a linux box, there will be equivalent commands for the tools you have; the idea is still the same: to forward external's port 13389 to 192.168.8.y's port 3389, then use external's RDP client to connect to localhost:13389.

You refer to setting up the linux box's sshd correctly, but unless you've reconfigured it, the standard sshd setup is likely to support this just fine.