Gray Hat Hacking, Second Edition, 2nd Edition

Buffer Overflows

Now that you have the basics down, we can get to the good stuff.

As described in Chapter 6, buffers are used to store data in memory. We are mostly interested in buffers that hold strings. Buffers themselves have no mechanism to keep you from putting too much data in the reserved space. In fact, if you get sloppy as a programmer, you can quickly outgrow the allocated space. For example, the following declares a string in memory of 10 bytes:

char  str1[10];

So what happens if you execute the following?

strcpy (str1, "AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA");

Let’s find out.

//overflow.c
main(){
   char str1[10];                         //declare a 10 byte string
   //next, copy 35 bytes of "A" to str1
   strcpy (str1, "AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA");
}

Then ...