Microsoft KB Archive/253943

= Windows Media Service Handshake Vulnerability =

Article ID: 253943

Article Last Modified on 10/26/2007

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APPLIES TO

 Microsoft Windows Media Services 4.0, when used with:  Microsoft Windows 2000 Standard Edition

 Microsoft Windows NT 4.0  Microsoft Windows Media Services 4.1, when used with:  Microsoft Windows 2000 Standard Edition

 Microsoft Windows NT 4.0</li></ul> </li> Microsoft NetShow Theater Server 3.0</li> Microsoft NetShow 4.0</li></ul>

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This article was previously published under Q253943

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SYMPTOMS
An access violation occurs when the Windows Media Unicast Service (Nsum.exe) tries to access an invalid memory address.

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CAUSE
The problem occurs when a client sends a rogue packet to the Windows Media Unicast Server or when the server is programmatically attacked.

The handshake sequence between a Windows Media server and a Windows Media Player is asynchronous, because certain resource requests are dependent on the successful completion of previous ones. If the client-side handshake packets are sent in a particular misordered sequence, with certain timing constraints, the server attempts to use a resource before it has been initialized, and then fails catastrophically, causing the Windows Media Unicast Service to stop responding.

You can put the Windows Media Unicast Service back into normal operating condition by restarting the service, but any sessions that were in effect at the time of the failure need to be restarted.

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RESOLUTION
To resolve this problem, obtain the latest service pack for Windows 2000. For additional information, click the following article number to view the article in the Microsoft Knowledge Base:

260910 How to Obtain the Latest Windows 2000 Service Pack

Do not apply either of these patches to NetShow 2.0 or later. If you are running NetShow 2.0 or later, upgrade to Windows Media Services 4.1 and then apply the patch. For information on upgrading to Windows Media Services 4.1, click the Microsoft web site below:

http://technet.microsoft.com/en-us/library/bb676148.aspx

Windows Media Services 4.1 on Windows 2000
The following file is available for download from the Microsoft Download Center:

Download Wmsu8654_win2000.exe now

For additional information about how to download Microsoft Support files, click the following article number to view the article in the Microsoft Knowledge Base:

119591 How to Obtain Microsoft Support Files from Online Services

Microsoft scanned this file for viruses. Microsoft used the most current virus-detection software that was available on the date that the file was posted. The file is stored on security-enhanced servers that help to prevent any unauthorized changes to the file.

Windows Media Services 4.1 on Windows NT 4.0
The following file is available for download from the Microsoft Download Center:

Download Wmsu8654_nt4.exe now

For additional information about how to download Microsoft Support files, click the following article number to view the article in the Microsoft Knowledge Base:

119591 How to Obtain Microsoft Support Files from Online Services

Microsoft scanned this file for viruses. Microsoft used the most current virus-detection software that was available on the date that the file was posted. The file is stored on security-enhanced servers that help to prevent any unauthorized changes to the file.

The English version of this fix should have the following file attributes or later:

<pre class="fixed_text">  Date        Time    Version      Size    File name --  01/26/2000  11:53a  4.1.0.3857  436,672  Nsum.exe

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STATUS
Microsoft has confirmed that this is a problem in the Microsoft products that are listed at the beginning of this article. This problem was first corrected in Windows 2000 Service Pack 1.

Additional query words: Wmsu8654_win2000 WMSU4954_NT4 Netshow WMT Unicast C0000005 av

Keywords: kbhotfixserver kbqfe kbdownload kbbug kbfix kbgraphxlinkcritical kbqfe kbwin2000sp1fix KB253943

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