Microsoft Security Bulletin MS00-027 - Important
Patch Available for "Malformed Environment Variable" Vulnerability
Published: April 20, 2000
Originally Posted: April 20, 2000
Microsoft has released a patch that eliminates a security vulnerability in Microsoft® Windows NT® 4.0 and Windows® 2000. The vulnerability could allow a malicious user to make some or all of the memory on an affected server unavailable, potentially slowing or stopping an affected server's response time.
Frequently asked questions regarding this vulnerability and the patch can be found at http://www.microsoft.com/technet/security/bulletin/fq00-027.mspx
CMD.EXE, the command processor for Windows NT 4.0 and Windows 2000, has an unchecked buffer in part of the code that handles environment strings. Although we believe that it could not be exploited to run arbitrary code, it could be used to mount denial of service attacks in certain cases. If a server provides batch or other script files, a malicious user could potentially provide arguments that would create an extremely large environment string and overflow the buffer. This would cause the process to fail, and the memory allocated to the process would not be made available again until a dialogue had 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 server temporarily unavailable.
As noted above, Microsoft believes that arbitrary code cannot be made to execute via this vulnerability. The machines most likely to be affected would be web servers, as they are the most likely types of machines to offer batch files for use by remote users. However, even an otherwise-affected web server would not be vulnerable to this problem if an operator were present at the console to clear the error dialogue promptly.
Affected Software Versions
- Microsoft Windows NT 4.0 Workstation
- Microsoft Windows NT 4.0 Server
- Microsoft Windows NT 4.0 Server, Enterprise Edition
- Microsoft Windows NT 4.0 Server, Terminal Server Edition
- Microsoft Windows 2000 Professional
- Microsoft Windows 2000 Server
- Microsoft Windows 2000 Advanced Server
Vulnerability Identifier: CVE-2000-0331
- Windows NT 4.0: http://www.microsoft.com/downloads/details.aspx?FamilyId=F403EC53-9726-42A1-AAAC-95772ED06A9A&displaylang=en
- Windows 2000: http://www.microsoft.com/downloads/details.aspx?FamilyId=2D8C75EA-01FA-45CE-A448-4AFE869D1782&displaylang=en
- Microsoft Windows NT 4.0 Server, Terminal Server Edition: http://www.microsoft.com/downloads/details.aspx?FamilyId=9BDDD606-12B6-43BF-A4EC-2AD96695950D&displaylang=en
Note: Additional security patches are available at the Microsoft Download Center
Please see the following references for more information related to this issue.
- Frequently Asked Questions: Microsoft Security Bulletin MS00-027, http://www.microsoft.com/technet/security/bulletin/fq00-027.mspx
- Microsoft Knowledge Base (KB) article 259622, http://support.microsoft.com/default.aspx?scid=kb;en-us;259622
- Microsoft TechNet Security web site, http://www.microsoft.com/technet/security/default.mspx
Obtaining Support on this Issue
This is a fully supported patch. Information on contacting Microsoft Technical Support is available at http://support.microsoft.com/contactussupport/?ws=support.
- April 20, 2000: Bulletin Created.
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