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Microsoft Security Bulletin (MS99-029)
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Patch Available for "Malformed HTTP Request Header" Vulnerability
Originally Posted: August 11, 1999
Re-released: August 16, 1999
Summary
=======
Microsoft has released a patch that eliminates a vulnerability in web server
products that use Microsoft(r) Internet Information Server 4.0 as their web
engine. The vulnerability could be used to mount denial of service attacks
against the web server. This patch originally was released on August 11,
1999, but was found to contain a regression error. The regression error has
been eliminated and the new patch is now available.
Frequently asked questions regarding this vulnerability can be found
at http://www.microsoft.com/security/bulletins/MS99-029faq.asp
Issue
=====
If multiple HTTP requests containing specially-malformed headers are sent to
an affected server, IIS may consume all memory on the server. If this
happens, IIS would be unable to service requests until either the clients
that issued the requests were closed, or the IIS service were stopped and
restarted. Once either of these actions have occurred, normal service would
be restored.
Affected Software Versions
==========================
- Microsoft Internet Information Server 4.0
Note: Although the vulnerability lies in IIS 4.0, several other Microsoft
products also are affected because they use IIS 4.0 as their web engine.
The patch can be applied to these products as well:
- Microsoft Site Server 3.0
- Microsoft Site Server 3.0, Commerce Edition
- Microsoft Commerce Internet Server 2.0 and 2.5
Patch Availability
==================
- ftp://ftp.microsoft.com/bussys/iis/iis-public
/fixes/usa/security/HDBRK-fix/
Note: Line breaks have been inserted into the above URL for readability
More Information
================
Please see the following references for more information related to this
issue.
- Microsoft Security Bulletin MS99-029: Frequently Asked Questions,
http://www.microsoft.com/security/bulletins/MS99-029faq.asp.
- Microsoft Knowledge Base (KB) article Q238349,
Specially-Malformed Header in HTTP Request Creates Denial of Service,
http://support.microsoft.com/support/kb/articles/q238/3/49.asp.
(Note: It may take 24 hours from the original posting of this
bulletin for the KB article to be visible.)
- Microsoft Security Advisor web site,
http://www.microsoft.com/security/default.asp.
Obtaining Support on this Issue
===============================
This is a fully supported patch. Information on contacting Microsoft
Technical Support is available at
http://support.microsoft.com/support/contact/default.asp.
Acknowledgments
===============
Microsoft acknowledges Nobuo Miwa of the LAC SNS team for bringing this
issue to our attention and working with us to alert customers about it.
Revisions
=========
- August 11, 1999: Bulletin Created.
- August 16, 1999: Patch re-released
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