Microsoft Security Bulletin (MS00-029)
Patch Available for "IP Fragment Reassembly" Vulnerability
Originally Posted: May 19, 2000
Microsoft has released a patch that eliminates a security vulnerability in Microsoft(r) Windows(r) 95, Windows 98, Windows NT(r) 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.asp
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.
Note: Line breaks have been inserted into the URLs above for readability.
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 MS00-029, http://www.microsoft.com/technet/security/bulletin/fq00-029.asp - Microsoft Knowledge Base article Q259728 discusses this issue and will be available soon. - 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.asp
This is a fully supported patch. Information on contacting Microsoft Technical Support is available at http://support.microsoft.com/support/contact/default.asp.
Microsoft thanks Bindview's RAZOR Security Team (http://www.bindview.com) for reporting this issue to us and working with us to protect customers.
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Last updated May 19, 2000