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Microsoft Security Bulletin (MS00-029)

Patch Available for "IP Fragment Reassembly" Vulnerability

Originally Posted: May 19, 2000

Summary

Microsoft has released a patch that eliminates a security vulnerability in Microsoft® Windows® 95, Windows 98, Windows NT® 4.0 and Windows 2000. The vulnerability could be used to cause an affected machine to temporarily stop performing useful work.

Frequently asked questions regarding this vulnerability and the patch can be found at http://www.microsoft.com/technet/security/bulletin/fq00-029.mspx

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General Information

Issue

The affected systems contain a flaw in the code that performs IP fragment reassembly. If a continuous stream of fragmented IP datagrams with a particular malformation were sent to an affected machine, it could be made to devote most or all of its CPU availability to processing them. The data rate needed to completely deny service varies depending on the machine and network conditions, but in most cases even relatively moderate rates would suffice.

The vulnerability would not allow a malicious user to compromise data on the machine or usurp administrative control over it. Although it has been reported that the attack in some cases will cause an affected machine to crash, affected machines in all Microsoft testing returned to normal service shortly after the fragments stopped arriving. Machines protected by a proxy server or a firewall that drops fragmented packets would not be affected by this vulnerability. The machines most likely to be affected by this vulnerability would be machines located on the edge of a network such as web servers or proxy servers.

Affected Software Versions

•	Microsoft Windows 95
•	Microsoft Windows 98
•	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-2000-0305

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Patch Availability

•	Windows 95: http://download.microsoft.com/download/win95/update/8070/w95/EN-US/259728USA5.EXE
•	Windows 98: http://download.microsoft.com/download/win98/update/8070/w98/EN-US/259728USA8.EXE
•	Windows NT 4.0 Workstation, Server and Server, Enterprise Edition: http://www.microsoft.com/downloads/details.aspx?FamilyId=7075667C-C667-4BCB-BEAC-FCA6EE1E770B&displaylang=en
•	Windows NT 4.0 Server, Terminal Server Edition: http://www.microsoft.com/downloads/details.aspx?FamilyId=04918303-4AC9-47BC-A289-84D08DF2DB63&displaylang=en
•	Windows 2000 Professional, Server and Advanced Server: http://www.microsoft.com/downloads/details.aspx?FamilyId=43065EB6-F04D-4FB0-809C-D8BACACBBE05&displaylang=en

Note Additional security patches are available at the Microsoft Download Center

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More Information

Please see the following references for more information related to this issue.

•	Frequently Asked Questions: Microsoft Security Bulletin MS00-029, http://www.microsoft.com/technet/security/bulletin/fq00-029.mspx
•	Microsoft Knowledge Base (KB) article 259728, http://support.microsoft.com/default.aspx?scid=kb;en-us;259728&sd=tech
•	RFC 791, Internet Protocol, http://www.ietf.org/rfc/rfc0791.txt?number=791
•	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.

Acknowledgments

Microsoft thanks Bindview's RAZOR Security Team for reporting this issue to us and working with us to protect customers.

Revisions

•	May 19, 2000: Bulletin Created.

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