Malformed Environment Variable Vulnerability

A security vulnerability exists in Microsoft® Windows NT® 4.0 and Windows® 2000 which 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.

Issue

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.

Affected Products

• Windows NT/2000

Solution

Software patches are available from the following locations:

• Windows NT 4.0: http://www.microsoft.com/Downloads/Release.asp?ReleaseID=20494
• Windows 2000: http://www.microsoft.com/Downloads/Release.asp?ReleaseID=20503
• Microsoft Windows NT 4.0 Server, Terminal Server Edition: http://www.microsoft.com/Downloads/Release.asp?ReleaseID=20586

Further Details

Source: Microsoft Corporation

Reference: Microsoft Corporation

Updated: April 20, 2000

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