Windows MRXSMB.SYS MRxSmbCscIoctlOpenForCopyChunk Overflow
iDefense Security Advisory 06.13.06
June 13, 2006
Microsoft Windows Operating System is system software for Intel based
PCs. More information can be found at the vendor website:
Local exploitation of a buffer overflow vulnerability in Microsoft
Corp.'s Windows Operating System could allow attackers to gain SYSTEM
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, which 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 MrxSmbCscIoctlOpenForCopyChunk()
function. In order to establish communication with the MRXSMB subsystem,
a file handle to a shadow device is created and DeviceIoControl() is
used to issue commands. If an attacker utilizes the METHOD_NEITHER
method flag, the address will be unchecked and an overwrite of kernel
memory can occur resulting in ring0 code execution.
Successful exploitation of this vulnerability could result in elevation
to SYSTEM privileges.
iDefense has confirmed the existence of this vulnerability in Microsoft
Windows XP SP2. It is suspected that all versions of Microsoft Windows
iDefense is unaware of any effective workaround for this issue.
VI. VENDOR RESPONSE
The vendor security advisory and appropriate patches are available at:
VII. CVE INFORMATION
The Common Vulnerabilities and Exposures (CVE) project has assigned the
name CAN-2006-2373 to this issue. This is a candidate for inclusion in
the CVE list (http://cve.mitre.org), which standardizes names for
VIII. DISCLOSURE TIMELINE
12/09/2005 Initial vendor notification
12/13/2005 Initial vendor response
06/13/2006 Coordinated public disclosure
iDefense credits Rub=E9n Santamarta with the discovery of this
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X. LEGAL NOTICES
Copyright =A9 2006 iDefense, Inc.
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