Reverse Pimpage is a tool for allowing one to telnet backwards through a firewall, assuming the box is allowed to make outgoing tcp connections. You have to be able to get access to the inside machine first, though, to get the client on the machine.
You can download it from the following link: https://packetstormsecurity.com/files/download/10475/rpv21.tar.gz
Source: https://packetstormsecurity.com/files/10475/rpv21.tar.gz.html