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Anti-debugging tricks revealed – Defcon CTF Qualifications 2009: Bin300 Analysis


A while ago I stumbled upon an awesome write-up of a very nice CTF challenge created by sapheads:

I love cartoons, and I love reversing, so I decided to play a little bit with that binary (b300.exe) which was a lot of fun.

Because some interesting anti-debugging tricks were implemented into the binary, I decided to make a short video about the reversing process.

First of all, thanks to KorUPt and Sapheads ( for the awesome cartoon.
At the time of creating this video, the binary and KOrUPt’s write-up are available here:§ion=attach&attach_id=2736

Finally, thanks to Defcon and DDTek for this great challenge !



You can view a full screen version here

You can download the movie here

© 2011, Corelan Team (fancy). All rights reserved.

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3 Responses to Anti-debugging tricks revealed – Defcon CTF Qualifications 2009: Bin300 Analysis

  • johnnycannuk says:

    Nice…I learned of a few new anti-debug techniques. Doesn’t Immunity’s !hidedebug option patch for these?

    • Corelan Team (fancy) says:

      Nice, thanks.
      Unfortunately hidedebug doesn’t help here.

      1. int3 : it is the debuggers way to set software breakpoints, so it’s a legitimate code. The debugger cannot determine if it is meant for sth. else – the debugger always thinks it’s a software breakpoint.

      2. int 2D: since its exception value is used later to form the start address of the execption handler, there’s no way for patching too. For OllyDbg there is a plugin called StrongOD which claims to “correctly handle the instructions int 2d” but I’m not aware of if it can help in this case. I would say

  • johnnycannuk says:

    Ok good to know…I’ll have to study this more closely in case I run into it in the field.

    Thanks again.

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