Exploit writing-1

Hi guyzzz ..  Today we will be learning about the exploit writing .

Before we move further i am assuming few things

1)You understand the basic concept  of the buffer overflows
2)You know basic C/C++ and ASM knowledge
3)Basic knowledge about  the GDB
4)Exploiting techniques

If you dnt know about anyone of the above assumptions , please learn them and come back

First of all let me write small c program

#include<stdio.h>
#include<string.h>
int main ( int argc , char** argv[])
{
char buff[500];
strcpy(buff,argv[1]);
}

Lets see what happens if you compile the above program  and load it in the debugger

What is happening and why it is happening ???
well gcc 3.x and gcc 4.x by default use a protecting technique called "stack smashing protection " , which is used for tracing the stack buffer overflow before any malicious code is executed

Stack Smashing protection 


SSP places a randomly chosen integer in memory just befor the stack return pointer . Normallt , buffer overflows overwrite memory addresses from low to high , so in order to overwrite the small integer that is placed just befor the stack return pointer , SSP just checks to see if that integer was changed or not before the use of the return pointer on the stack

How to bypass the SSP ?? 


we can bypass the SSP by adding "-fno-stack-protector" flag to gcc when compiling


we will discuss further in the next tutorial ... Thank you 

Posted in: Exploits