Microsoft WinNT/2000 'Malformed Environment Variable' Vulnerability patch - Version 1 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. 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. 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.