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Microsoft Client Server Runtime System Vulnerability

Vulnerability Note VU#259197

Original Release Date: 2005-04-13 | Last Revised: 2005-05-17


The Microsoft Client Server Runtime System (CSRSS) incorrectly validates certain messages potentially resulting in privilege elevation.


CSRSS is the user-mode part of the Win32 subsystem. Win32.sys is the kernel-mode portion of the Win32 subsystem. The Win32 subsystem must be running at all times. CSRSS is responsible for console windows, for creating threads, for deleting threads, and for some parts of the 16-bit virtual MS-DOS environment. The CSRSS only responds to requests made by other processes on the local computer.

A locally authenticated user may be able to exploit a vulnerability in the way CSRSS validates certain messages in order to gain elevated privileges.


Local authenticated users could potentially execute arbitrary code as privileged users, allowing them to gain complete control of the system.


Apply a patch

Microsoft has published Microsoft Security Bulletin MS05-018 in response to this issue. Users are strongly encouraged to review this advisory and apply the patches it refers to.

Vendor Information


Microsoft Corporation Affected

Updated:  April 13, 2005



Vendor Statement

For more information please see Microsoft bulletin MS05-018 available at:

Vendor Information

The vendor has not provided us with any further information regarding this vulnerability.


US-CERT has no additional comments at this time.

If you have feedback, comments, or additional information about this vulnerability, please send us email.

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Thanks to Microsoft who in turn thank David Fritz working with iDEFENSE for reporting the CSRSS Vulnerability.

This document was written by Robert Mead based on information provided by Microsoft.

Other Information

CVE IDs: CVE-2005-0551
Severity Metric: 2.43
Date Public: 2005-04-12
Date First Published: 2005-04-13
Date Last Updated: 2005-05-17 14:10 UTC
Document Revision: 15

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