Microsoft has identified a vulnerability in the computer browser protocol ResetBrowser frame that could allow a malicious user to shut down a computer browser on the same subnet, or shut down all of the computers browsers on the same subnet. If all of the computers on the same subnet are shut down, they can then declare their own computer the new master browser.

NOTE: If a firewall is in place and port 138 UDP is blocked, this vulnerability cannot be exploited by an external user.

Additional information about this issue is available from the following Microsoft Web site:

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This behavior occurs because the ResetBrowser frame allows browsers to be shut down, but does not allow for a computer to ignore the ResetBrowser frames request.

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Windows 2000

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: After you apply the following patch, you can configure computers to refuse ResetBrowser packets. This update is part of the Windows 2000 Security Update, June 6, 2000 that is available on the Windows Update (http://windowsupdate.microsoft.com/) site. You can also download this critical update (for installation later or on a different computer) from the following Microsoft Web sites: The English-language version of this fix should have the following file attributes or later:

   Date        Time     Version         Size     File name
   --------------------------------------------------------
   05/16/2000  07:35p   5.0.2195.2096   368,976  Mrxsmb.sys
				

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Windows NT 4.0

To resolve this problem, obtain the individual package referenced below or obtain the Windows NT 4.0 Security Rollup Package. For additional information on the SRP, click the article number below to view the article in the Microsoft Knowledge Base: The following files are available for download from the Microsoft Download Center:

US English:

x86: Alpha: For additional information about how to download Microsoft Support files, click the following article number to view the article in the Microsoft Knowledge Base: 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-language version of this fix should have the following file attributes or later:

   Date        Time    Size     File name  Platform
   ------------------------------------------------
   05/22/2000  08:34p  265,712  Rdr.sys    x86
   05/22/2000  08:32p  508,720  Rdr.sys    Alpha
				

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Microsoft Windows NT Server version 4.0, Terminal Server Edition

To resolve this problem, obtain the Windows NT Server 4.0, Terminal Server Edition, Security Rollup Package (SRP). For additional information about the SRP, click the article number below to view the article in the Microsoft Knowledge Base:

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Windows 2000

Microsoft has confirmed that this problem may cause a degree of security vulnerability in Windows 2000. This problem was first corrected in Windows 2000 Service Pack 2.

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Windows NT 4.0

Microsoft has confirmed that this problem may cause a degree of security vulnerability in Windows NT 4.0 and Windows NT Server version 4.0, Terminal Server Edition.

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WARNING: If you use Registry Editor incorrectly, you may cause serious problems that may require you to reinstall your operating system. Microsoft cannot guarantee that you can solve problems that result from using Registry Editor incorrectly. Use Registry Editor at your own risk.

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RefuseReset Registry Entry

The patch provides functionality that allows an administrator to configure a computer to ignore ResetBrowser frames. To implement the patch, create the following registry key: NOTE: Set the DWORD value of the key to 0x01 to ignore ResetBrowser frames and to None to accept ResetBrowser frames.

For additional information about what this patch fixes in Windows NT 4.0, click the article number below to view the article in the Microsoft Knowledge Base:

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