MS00-027: Command Processor May Not Parse Excessive Arguments Properly

It may be possible (under specific conditions) for a malicious user to submit an excessively long environment string to be passed to the command processor on a computer running Windows NT 4.0 or Windows 2000 and cause the computer to stop responding (hang).

The most commonly affected computers are likely to be Web servers that are remotely administered in a so-called "headless" configuration. Exploiting this vulnerability consumes memory on the computer, thereby slowing its response or preventing it from providing useful services altogether. This vulnerability cannot be used to compromise data, run arbitrary code on the computer, or to usurp administrative control. The vulnerability can be exploited only under very specific conditions that are not present on all computers. Moreover, coding practices in batch and script files can prevent this vulnerability from manifesting itself on an otherwise-affected computer.

The command processor (Cmd.exe) for Windows NT 4.0 and Windows 2000 has an unchecked buffer in part of the code that handles environment strings. If a computer provides batch or other script files, a malicious user could potentially provide arguments that create an extremely large environment string and overflow the buffer. This overflow may cause the batch process to hang; the memory allocated to the process is not made available again until a dialog box has been cleared on the operator's console. By repeatedly running the batch file, the malicious user could potentially make some or all of the memory on the computer temporarily unavailable.

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.

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:
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 secure servers that prevent any unauthorized changes to the file.

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

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:
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 secure servers that prevent any unauthorized changes to the file.

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

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 1.

Windows NT 4.0

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

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.

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: