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Vulnerability Note VU#910998Microsoft Windows kernel fails to properly handle invalid opcodes used in DOS emulationOverviewA vulnerability in the way the Microsoft Windows kernel handles invalid opcodes used in DOS emulation could allow a local attacker to gain elevated privileges on a vulnerable system.I. DescriptionThe Virtual DOS Machine (VDM) provides support for 16-bit legacy operations and applications. For instance, a VDM is started when a user executes a MS-DOS application. The Windows kernel is responsible for handling 16-bit code executed inside a VDM. There is a vulnerability in the way the Windows kernel validates memory locations allocated to a VDM. After processing an invalid opcode byte sequence, the kernel fails to validate the memory address where execution should be transferred allowing an attacker to redirect this execution to arbitrary locations in memory. Exploitation of this vulnerability could allow a local, authenticated attacker to execute arbitrary code on an affected system with kernel privileges.Microsoft reports that this is not the same vulnerability described in MS04-011.
Microsoft has provided a patch to address this vulnerability. For a list of affected versions and details on obtaining the patch, please refer to Microsoft Security Bulletin MS04-032.
References
This vulnerability was reported by Microsoft. Microsoft credits eEye Digital Security for discovering the vulnerability. This document was written by Damon Morda based on information contained in the eEye Advisory.
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