Redirect output of a program that executes shellcode

Question

i have this little program that executes a shellcode:

#include<stdio.h>
#include<string.h>
#include<stdlib.h>

char shellcode[]="here is the bytecode";


int main(int main, char *argv[]) {
      void (*ret)();
      ret = (void (*)())shellcode;
      (void)(*ret)();
}

i compile it with: gcc -o file file.c -fno-stack-protector -z execstack. Then i try to redirect the output to a file: ./file > tmp.txt But it doesn't work. Neither this: ./file 2> tmp.txt or ./file &> tmp.txt

The output is always printed to the screen, never to the file. Can anyone help me? I really need the output of that shellcode.

What does the shellcode do? How does it print its output?

Etan Reisner
– Etan Reisner

2015-02-26 14:36:58 +00:00
Commented Feb 26, 2015 at 14:36 — Etan Reisner
– Etan Reisner, Commented Feb 26, 2015 at 14:36

ccarton · Accepted Answer · 2015-02-26 17:21:47Z

1

If redirecting stdout and stderr doesn't work then the program is likely accessing the terminal directly. To capture direct terminal output you need to launch the program with a pseduo-tty connected. The easiest way to do that (that I'm aware of) is to use ssh. Try:

ssh -qt localhost "./file" > tmp.txt 2>&1

You'll want to install ssh keys to avoid having to enter login credentials.

Edit: Oops, my redirections were in the wrong order. Rookie mistake.

edited Feb 26, 2015 at 17:21

answered Feb 26, 2015 at 15:49

ccarton

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