Buffer Overflow Explained

Hello, and welcome to pwn.guide! In this tutorial, we will explore one of the most common and dangerous hacking techniques - buffer overflow.

What is Buffer Overflow?

Buffer Overflow is a technique that hackers use to exploit vulnerabilities in software. In this attack, the hacker overflows a buffer in a program by inputting data that exceeds the maximum size of the buffer. This extra data could contain arbitrary code that the hacker wants the program to execute.

How Does Buffer Overflow Work?

Let us take a look at an example. Suppose we have a program that takes an input from the user and stores it in a buffer of size 10. Here is the code for the program:

#include<stdio.h>
#include<string.h>
void foo(char *str)
{
 char buffer[10];
 strcpy(buffer, str);
}
int main(int argc, char **argv)
{
 foo(argv[1]);
 return 0;
}

This program is vulnerable to buffer overflow because it does not check the size of the input string. If the user inputs more than 10 characters, the buffer will overflow and the program will behave in an unpredictable manner.

To exploit this vulnerability, a hacker can input a string with arbitrary code and overwrite the buffer. The following example input will open a shell on the target system:

./program `python -c 'print "A" * 10 + "\x0f\x85\x84\x04\x08\xc3"'`

This code will overflow the buffer and execute the arbitrary code that the hacker entered.

How to Prevent Buffer Overflow?

Preventing buffer overflow requires writing secure code by following coding best practices. Here are some tips:

• Always check the input size before storing it in a buffer.

• Use compiler flags such as -fstack-protector-strong to enable stack protection.

• Use a programming language that has built-in memory management such as Java or Python.

Conclusion

Buffer Overflow is a dangerous hacking technique that can exploit software vulnerabilities. To prevent it, remember to write secure code and always check the size of inputs before storing them in buffers.

Thank you for reading this tutorial!