Latest Windows 2000 patch can lock system

A software patch that fixes a serious security vulnerability in Microsoft Corp.'s Windows 2000 can cause systems running the operating system to fail, Microsoft said Tuesday.

The patch, announced Monday in security bulletin MS03-007, is incompatible with 12 software fixes for Windows 2000 issued by Microsoft's Product Support Services (PSS) between December 2001 and February 2002. Users running any of those fixes won't be able to reboot their Windows 2000 systems after applying the "critical" patch, according to a revised version of Microsoft's bulletin issued Tuesday.

Customers running Windows 2000 with Service Pack 2 installed should verify the version of a file called "ntoskrnl.exe" on their system before applying the patch. Versions of this file from 5.0.2195.4797 up to and including 5.0.2195.4928 were distributed by PSS and are not compatible with the patch, according to Microsoft.

Users who have an incompatible file on their system need to contact Microsoft PSS before applying the patch. If the patch is installed on a system with the incompatible file, the machine will fail on the first reboot and will have to be recovered using the Windows 2000 recovery console, Microsoft said.

The patch fixes a buffer overrun flaw in a component of Windows 2000 used by a feature that allows users to remotely manage Web site content on a Windows 2000 server. The Windows component is called "ntdll.dll" and the feature is called WebDAV, or World Wide Web Distributed Authoring and Versioning.

An attacker could gain full control over a vulnerable system by sending it a specially formed HTTP (Hypertext Transfer Protocol) request. Microsoft on Monday said it had received reports of attacks that exploit the new vulnerability. Experts have said that this is the kind of vulnerability exploited by malicious and fast spreading Internet worms such as Code Red and Nimda.

Windows 2000 users who don't immediately want to install the patch can take measures to block the WebDAV request used to exploit the vulnerability. These measures include removing Microsoft's Internet Information Server (IIS) Web server altogether, or locking down the system by running the IIS Lockdown tool. However, these workarounds should be temporary measures as they do not correct the underlying vulnerability, Microsoft said.

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