Question

What does this command do?

cat /tmp/f | /bin/sh -i 2>&1 | nc -l 1234 >/tmp/f

Answer 1

Simple webserver using netcat.You can think of it more simply as sh and nc are redirecting to each other in a loop. The rest of the command is just fluff.

• cat /tmp/f is printing whatever is written to that named pipe and the output of cat /tmp/f is been piped to /bin/sh

• /bin/sh is running interactively and stderr is redirected to stdout.
• `the output is then piped to nc which is listening on port 1234
• and the out put is finally redirected to the named pipe again.

when run, connecting to the remote server on that port i.e 1234 opens a shell prompt and the client can execute arbitrary commands.