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Friday, August 23, 2013

IE heaps at Nordic Security Conference

By Chris Valasek @nudehaberdasher

Remember when I used to be the Windows Heap guy? Yeah, me neither ;). I just wanted to give everyone a heads up regarding my upcoming presentation “An Examination of String Allocations: IE-9 Edition” at Nordic Security Conference (www.nsc.is). The presentation title is a bit vague so I figured I would give a quick overview.

First, I’ll briefly discuss the foundational knowledge regarding heap based memory allocations using JavaScript strings in IE-6 and IE-7. These technics to manipulate the heap are well documented and have been known for quite some time [1].

While heap spraying and allocation techniques have continued to be used, public documentation of such techniques has been lacking. I specifically remember Nico Waisman talking about using the DOM [2] to perform precise allocations, but I don’t recall specific details being released. Nico’s presentation inspired me to reverse engineer a small portion of IE-9’s JavaScript implementation when it came to string based memory manipulation techniques. (Editor’s note: I’ve been holding onto this for 2 years, WTF Chris?).

Next I’ll cover, in detail, the data structures and algorithms used in IE-9 that are common during the exploitation process when performing typical string manipulations. Hopefully the details will give insight into what actually happens for vanilla exploitation attempts.

Lastly, I’ll demo a library which I’m calling heapLib2. HeapLib2 is an extension of Alex Sotirov’s original heap library that will work with modern versions of Internet Explorer when requiring precise heap-based allocations. You can now do some neat memory tricks with a few simple lines.




One final reflection; if you haven’t been to Nordic Security Conference (or Iceland in general) you should consider going. The conference has an attentive but laid back atmosphere while providing both highly technical and high level security presentations. If you’ve been looking for an excuse to go to Iceland get yourself to Nordic Security Conference!


P.S. These techniques _MAY_ work with versions of IE that are greater than version 9

P.P.S. Ok, they DO work.

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