The art of reverse engineering flash exploits

The art of reverse engineering flash exploits

Adobe Flash is one of the battlegrounds of exploit and mitigation methods. As most of the Flash exploits demonstrate native memory layer exploit technique, it is valuable to understand the memory layout and behavior of Adobe Flash Player. We developed fine-grained debugging tactics to observe memory exploit technique and the way to interpret them effectively. This eventually helps defenders to understand new exploit techniques that are used for current targets quickly. This information is also valuable in deciding which area should defenders focus on for mitigation and code fixes. Adobe Flash Player was one of the major attack targets in 2015. We observed at least 17 effective zero-days or 1-day attacks in the wild. Flash is not just used by exploit kits like Angler, it has also been commonly used for advanced persistent threat (APT) attacks. The bug class ranges from simple heap overflows, uninitialized memory to type confusion and use-after-free. At Microsoft, understanding exploits in-the-wild is a continuous process. Flash exploit is one of the hardest to reverse-engineer. It often involves multi-layer obfuscation, and by default, is highly obfuscated and has non-decompilable codes. The challenge with Flash exploit comes from the lack of tools for static and dynamic analysis. Exploits are written with ActionScript programming language and obfuscated in bytecode level using commercial-grade obfuscation tools. Understanding highly obfuscated logic and non-decompilable AVM bytecode is a big challenge. Especially, the lack of usable debuggers for Flash file itself is a huge hurdle for exploit reverse engineers. It is just like debugging PE binaries without using Windbg or Olly debugger. The ability of the researcher is highly limited. 
With this presentation, I want to deliver two things: 1. The tactics and debugging technique that can be used to reverse engineer exploits. This includes using existing toolsets and combining them in an effective way. 2. The detailed exploit code reverse engineering examples that can help you understand what's the current and past status of attack and mitigation war. You might have heard of Vector corruption, ByteArray corruption and other JIT manipulation technique. Technical details will be discussed on how the exploits are using these and how the vendor defended against these.


Jeong Wook Oh

Jeong Wook Oh is a passionate security researcher. He made DarunGrim - an opensource binary diffing tool. Currently he's at Microsoft fighting APT and exploits. Analyzing hard to crack exploit cases is one of his fun things in his job.

Detailed Presentation:

(Source: Black Hat USA 2016, Las Vegas)


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