Small ICMP backdoor which works under BSD, Linux, and Solaris. Because you can define the icmp_code to use it is able simulate an echo_request <-> echo_reply conversation so it looks like a normal ping with bigger packets. It also includes a session_id to detect the right packets (which is also done by certain icmp_id’s).
You can download it from the following link: https://packetstormsecurity.com/files/download/26159/icmp-backdoor.tar.gz
Source: https://packetstormsecurity.com/files/26159/icmp-backdoor.tar.gz.html