Stack One

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 can be found at /opt/phoenix/<architecture>/stack-one


  • man ascii can tell you what the hexadecimal characters are.
  • Having troubles? How does the endianness of the architecture affect the layout of how variables are laid out?

Source code

 * phoenix/stack-one, by
 * 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"

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",