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Windows MRXSMB.SYS MrxSmbCscIoctlCloseForCopyChunk DoS

06.13.06

BACKGROUND

Microsoft Windows Operating System is system software for Intel based
PCs. More information can be found at the vendor website:

   http://www.microsoft.com

DESCRIPTION

Local exploitation of an access validation error in Microsoft Corp.'s
Windows Operating System could allow attackers to cause a denial of
service (DoS) condition.

The vulnerability specifically exists due to a logic error in the
Microsoft Client Side Caching (CSCDLL.DLL) and Microsoft Server Message
Block Redirector Driver (MRXSMB.SYS) code. The Microsoft Client Side
Caching infrastructure provides the user-mode portion of the "offline
files" subsystem that allows interaction with network files while
offline and preserves file system permissions. The Microsoft Server
Message Block Redirector Driver is the kernel-mode file system driver
that provides the network redirector functionality utilized by CSC.

MRXSMB.SYS functions are exposed via IOCTL commands. An access
validation error exists in the MrxSmbCscIoctlCloseForCopyChunk()
function. In order to establish communication with the MRXSMB subsystem,
a file handle to a shadow device is created. If the
MrxSmbCscIoctlCloseForCopyChunk() function is passed the file handle to
the shadow device, a deadlock occurs, resulting in an unkillable
process.

ANALYSIS

Exploitation could result in the creation of unkillable processes. This
attack can be used as protection against anti-virus or other host-based
intrusion prevention systems.

DETECTION

iDefense has confirmed the existence of this vulnerability in Microsoft
Windows XP SP2. It is suspected that all versions of Microsoft Windows
are vulnerable.

WORKAROUND

iDefense is unaware of any effective workaround for this issue.

VENDOR RESPONSE

The vendor security advisory and appropriate patches are available at:

   http://www.microsoft.com/technet/security/Bulletin/MS06-030.mspx

CVE INFORMATION

The Common Vulnerabilities and Exposures (CVE) project has assigned the
name CAN- 2006-2374 to this issue. This is a candidate for inclusion in
the CVE list (http://cve.mitre.org), which standardizes names for
security problems.

DISCLOSURE TIMELINE

02/07/2006   Initial vendor notification
02/07/2006   Initial vendor response
06/13/2006   Coordinated public disclosure

CREDIT

iDefense credits Rubén Santamarta with the discovery of this
vulnerability.

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LEGAL NOTICES

Copyright © 2006 Verisign, Inc.

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Disclaimer: The information in the advisory is believed to be accurate
at the time of publishing based on currently available information. Use
of the information constitutes acceptance for use in an AS IS condition.
There are no warranties with regard to this information. Neither the
author nor the publisher accepts any liability for any direct, indirect,
or consequential loss or damage arising from use of, or reliance on,
this information.