It may be possible for a malicious user to place a program named Explorer.exe in the C:\ folder (the root of drive C) so that it is run in place of the standard Windows shell program. By default, the share permissions on the C:\ folder are set to Everyone Full Access. Anyone who has access to this share, either locally or through a network connection, can place a program there that is run before the Explorer.exe shell.

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This issue can occur when you start a program by using a registry key if the entry does not specify an absolute path. Without a complete path, a standard path search order is followed. For example, the Shell value in the HKEY_LOCAL_MACHINE\Software\Microsoft\Windows NT\CurrentVersion\Winlogon key has a default value of "Explorer.exe" without any path information. During startup, when this value is read (without an explicit path), Windows attempts to locate the program by using a folder search. Contrary to the Windows 2000 documentation, the C:\ folder is the first location that is checked. Any program located there that is named Explorer.exe is run in place of the correct shell program.

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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: The following files are available for download from the Microsoft Download Center:
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 version of this fix should have the following file attributes or later:

   Date      Time    Size     File name
   ---------------------------------------
   07/18/00  05:07p  331,536  Msgina.dll
   07/18/00  05:07p   17,680  Userinit.exe
				

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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:

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

   Date      Time    Size     File name   Platform
   -----------------------------------------------
   07/18/00  07:27p  124,176  Msgina.dll  Intel
   07/18/00  07:25p  160,528  Msgina.dll  Alpha
				

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Windows NT Server 4.0, Terminal Server Edition

To resolve this problem, either obtain the hotfix referenced in this section or 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: A supported fix is now available from Microsoft, but it is only intended to correct the problem that is described in this article. Apply it only to computers that are experiencing this specific problem.

To resolve this problem, contact Microsoft Product Support Services to obtain the fix. For a complete list of Microsoft Product Support Services phone numbers and information about support costs, visit the following Microsoft Web site:NOTE: In special cases, charges that are ordinarily incurred for support calls may be canceled if a Microsoft Support Professional determines that a specific update will resolve your problem. The usual support costs will apply to additional support questions and issues that do not qualify for the specific update in question.

The following files are available for download from the Microsoft Download Center:

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

   Date      Time    Size     File name   Platform
   -----------------------------------------------
   07/18/00  07:22p  207,120  Msgina.dll  Intel
   07/18/00  07:08p  259,344  Msgina.dll  Alpha
				

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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 Microsoft Windows NT 4.0.

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Windows NT Server 4.0, Terminal Server Edition

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

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For related information about this problem, please visit the following Microsoft Web site: For additional security-related information about Microsoft products, please visit the following Microsoft Web site: For additional information about how to install Windows 2000 and Windows 2000 hotfixes at the same time, click the article number below to view the article in the Microsoft Knowledge Base:

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