Buffer Overflow Primer Part 5 (Shellcode for Execve)

Welcome to Part 5 of the Buffer Overflow Primer. If you have not already done so, please start this series by viewing Part 1. The Buffer Overflow Primer requires that you know at least some basic Assembly Language. I have created a series of Assembly Language video tutorials for Hackers here, for those not familiar with the language.

In this video we will learn how to convert the shellcode created in the previous video to a more usable format. It is important to note that the shellcode in the previous video cannot be used as-is becuase it contains NULLs and hardcoded addresses. Thus we need to convert it into something which can be injected into a buffer - i.e. we need to remove the NULLs and setup relative addressing. This video will show how we can replace the NULLs in the shellcode with instructions which results in non-NULL shellcode. Also, we discuss in detail how we can setup relative addressing within the shellcode and modify it at runtime to make it work. This is probably the most important video in the series, if one wants to understand the shellcode generation process completely.

Please download ExecveShellCode.s and ShellCode.c before you view this video.

We hate these ADs as much as you do! Help us stay FREE and CLEAN by making a Generous Donation!

Vivek Ramachandran is a security evangelist and has been working in computer security related fields for the past 7 years. In 2007, Vivek spoke at world renowned conferences Defcon (WEP Cloaking Exposed) and Toorcon (The Caffe Latte Attack). The discovery of the Caffe Latte Attack was covered by CBS5 news, BBC online, Network World etc news agencies.In 2006, Vivek was announced as one of winners of the Microsoft Security Shootout contest held in India among 65,000 participants. He has also been a recipient of a Team Achievement at Cisco Systems for his work on 802.1x and Port Security modules on the Catalyst 6500 switches. Currently he spends all of his time maintaining Security- Freak.Net , SecurityTube.Net and is the co-founder of Axonize. Vivek, is a Bachelor in Electronics and Communications Engineering from the prestigious Indian Institute of Technology, Guwahati.You can contact him at vivek[at]securitytube.net