Tunnelshell is a client-server backdoor which uses fragmented packets to traverse firewalls. Written in C, tested on Linux.
You can download it from the following link: https://packetstormsecurity.com/files/download/25694/tunnelshell_v1.tgz
Source: https://packetstormsecurity.com/files/25694/tunnelshell_v1.tgz.html