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Windows Kernel-mode GS Cookies subverted (paper)
From: j00ru <j00ru.vx () gmail com>
Date: Tue, 11 Jan 2011 21:44:33 +0100
Hi, We've published a paper about reducing the effective entropy of GS cookies found in the Windows drivers (both 32 and 64bits). The document aims to outline some of the techniques, which can be employed to predict the cookie value of a kernel module with up to 50% accuracy. Experimental results included. http://vexillium.org/dl.php?/Windows_Kernel-mode_GS_Cookies_subverted.pdf More information is available on our blogs: http://j00ru.vexillium.org/?p=690 http://gynvael.coldwind.pl/?id=371 Abstract: This paper describes various techniques that can be used to reduce the effective entropy of GS cookies implemented in a certain group of Windows kernel-mode executable images by roughly 99%, or otherwise defeat it completely. This reduction is made possible due to the fact that GS uses a number of extremely weak entropy sources, which can be predicted by the attacker with varying (most often - very high) degree of accuracy. In addition to presenting theoretical considerations related to the problem, the paper also contains a great amount of experimental results, showing the actual success / failure rate of different cookie prediction techniques, as well as pieces of hardware-related information. Furthermore, some of the possible problem solutions are presented, together with a brief description of potential attack vectors against these enhancements. Finally, the authors show how the described material can be practically used to improve kernel exploits’ reliability - taking the CVE-2010-4398 kernel vulnerability as an interesting example. Comments are welcome! Take care, Matt "j00ru" Jurczyk, Gynvael Coldwind _______________________________________________ Full-Disclosure - We believe in it. Charter: http://lists.grok.org.uk/full-disclosure-charter.html Hosted and sponsored by Secunia - http://secunia.com/
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