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Protostar Stack1

About

This level looks at the concept of modifying variables to specific values in the program, and how the variables are laid out in memory.

This level is at /opt/protostar/bin/stack1

Hints

  • If you are unfamiliar with the hexadecimal being displayed, “man ascii” is your friend.
  • Protostar is little endian

Source code

(stack1.c) download
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#include <stdlib.h>
#include <unistd.h>
#include <stdio.h>
#include <string.h>

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

  if(argc == 1) {
      errx(1, "please specify an argument\n");
  }

  modified = 0;
  strcpy(buffer, argv[1]);

  if(modified == 0x61626364) {
      printf("you have correctly got the variable to the right value\n");
  } else {
      printf("Try again, you got 0x%08x\n", modified);
  }
}