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Credit:
The tool can be downloaded from:
http://peter.eluks.com/code/Unix/C/ICMP-Shell/
The information has been provided by Peter Kieltyka.
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ICMP Shell is a program written in C for the UNIX environment that allows an administrator to access their computer remotely via ICMP.
How does it work?
The ISHELL server is run in daemon mode on the remote server. When the server receives a request from the client it will strip the header and look at the ID field. If this matches the server then it will pipe the data to "/bin/sh". It will then read the results from the pipe and send them back to the client and the client prints the results to stdout.
By default the client and server send packets with an ICMP type of 0 (ICMP_ECHO_REPLY). However, this can be changed on both the client and server side. ISHELL does not care what type you send out from the client or server end, the types do not have to match.
ISHELL does not only pipe commands to a server and send back the output. It also works with interactive programs (i.e. gdb). However, there comes a minor problem from this. ISHELL cannot display a shell prompt (#). The reason for that is that there is no way to differentiate between commands in interaction with a program.
Firewall? No one said anything about a firewall!
By default ISHELL uses ICMP type 0 (ICMP_ECHO_REPLY) to send/receive. After a little bit of research it seems that ICMP type 0 works best with this program. Other types do work, however some kernels process ICMP_ECHO_REQUEST packets automatically (BSD) while others do not (Linux).
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