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Microsoft Security Bulletin (MS00-031)
- --------------------------------------
Patch Available for "Undelimited .HTR Request" and "File Fragment
Reading via .HTR" Vulnerabilities
Originally Posted: May 10, 2000
Summary
=======
Microsoft has released a patch that eliminates two security
vulnerabilities in Microsoft(r) Internet Information Server. The
vulnerabilities could, respectively, be used to slow an affected web
server's response or to obtain the source code of certain types of
files under very restricted conditions.
Frequently asked questions regarding these vulnerabilities
and the patch can be found at
http://www.microsoft.com/technet/security/bulletin/fq00-031.asp
Issue
=====
This patch eliminates two security vulnerabilities that are unrelated
except by virtue of the fact that both exist in the ISAPI extension
that provides web-based password administration via .HTR scripts.
- The "Undelimited .HTR Request" vulnerability is a denial
of service vulnerability. If a malicious user provided a
password change request that was missing an expected
delimiter, the algorithm would conduct an unbounded search.
This would prevent it from servicing additional .HTR requests,
and could also slow the overall response of the server.
- The ".HTR File Fragment Reading" vulnerability could allow
fragments of certain types of files to be read by providing a
malformed request that would cause the .HTR processing to be
applied to them. However, the vulnerability could only be
exploited under extremely restrictive conditions, and the
most valuable data in the files would be the least likely to
actually appear in the fragments sent to the user.
Neither of these vulnerabilities would allow data to be added, deleted
or changed on the server, nor would they allow any administrative
control on the server to be usurped. Although .HTR files are used to
allow web-based password administration, neither of these
vulnerabilities involve any weakness in password handling. Also, if
security best practices have been followed, and unneeded script
mappings have been removed, many customers will have removed the .HTR
script mapping and thus be unaffected by either vulnerability.
Affected Software Versions
==========================
- Internet Information Server 4.0
- Internet Information Server 5.0
Patch Availability
==================
- Internet Information Server 4.0:
http://www.microsoft.com/Downloads/Release.asp?ReleaseID=20905
- Internet Information Server 5.0:
http://www.microsoft.com/Downloads/Release.asp?ReleaseID=20903
Note: Additional security patches are available at the Microsoft
Download Center
More Information
================
Please see the following references for more information related to
this issue.
- Frequently Asked Questions: Microsoft Security Bulletin MS00-031,
http://www.microsoft.com/technet/security/bulletin/fq00-031.asp
- Microsoft Knowledge Base article Q260838 discusses the
"Undelimited .HTR Request" vulnerability and will be available
soon.
- Microsoft Knowledge Base article Q260069 discusses the "File
Fragment Reading via .HTR" vulnerabilty and will be available
soon.
- How to Change Windows NT Account Passwords Using Internet
Information Server (IIS) 4.0,
http://www.microsoft.com/technet/support/kb.asp?ID=184619
- Microsoft TechNet Security web site,
http://www.microsoft.com/technet/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 thanks Internet Security Systems' X-force
(http://xforce.iss.net/), and David Litchfield of Cerberus Information
Security, Ltd (http://www.cerberus-infosec.co.uk/), for reporting
these vulnerabilities to us, and working with us to protect
customers.
Revisions
=========
- May 10, 2000: Bulletin Created.
- -------------------------------------------------------------------
THE INFORMATION PROVIDED IN THE MICROSOFT KNOWLEDGE BASE IS PROVIDED
"AS IS" WITHOUT WARRANTY OF ANY KIND. MICROSOFT DISCLAIMS ALL
WARRANTIES, EITHER EXPRESS OR IMPLIED, INCLUDING THE WARRANTIES OF
MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. IN NO EVENT
SHALL MICROSOFT CORPORATION OR ITS SUPPLIERS BE LIABLE FOR ANY DAMAGES
WHATSOEVER INCLUDING DIRECT, INDIRECT, INCIDENTAL, CONSEQUENTIAL,
LOSS OF BUSINESS PROFITS OR SPECIAL DAMAGES, EVEN IF MICROSOFT
CORPORATION OR ITS SUPPLIERS HAVE BEEN ADVISED OF THE POSSIBILITY OF
SUCH DAMAGES. SOME STATES DO NOT ALLOW THE EXCLUSION OR LIMITATION OF
LIABILITY FOR CONSEQUENTIAL OR INCIDENTAL DAMAGES SO THE FOREGOING
LIMITATION MAY NOT APPLY.
Last updated May 10, 2000
(c) 2000 Microsoft Corporation. All rights reserved. Terms of use.
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On May 10, 2000, we released Microsoft Security Bulletin MS00-031
(http://www.microsoft.com/technet/security/bulletin/ms00-031.asp),
discussing a pair of vulnerabilities affecting Internet Information
Server (IIS) 4.0 and 5.0. Both of the vulnerabilities, known as the
"Undelimited HTR Request" and "File Fragment Reading via .HTR"
vulnerabilities, should have been eliminated by the patches discussed
in the bulletin. In the case of the IIS 4.0 patch, this was the case.
However, we have recently discovered that the IIS 5.0 patch only
eliminated the "Undelimited HTR Request" vulnerability, and not the
"File Fragment Reading via .HTR" vulnerability.
We have released a new version of IIS 5.0 patch, and have verified
that it does eliminate both vulnerabilities. We recommend that any
customers who previously applied the IIS 5.0 patch revisit the
bulletin and apply the new version of the patch, to ensure that they
are fully protected against both vulnerabilities. The IIS 4.0 patch
was always correct, and customers who applied it do not need to take
any action. We are very sorry for any inconvenience caused by this
error, and will do our best to ensure that it does not occur again.
Regards,
Secure@microsoft.com
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please visit http://www.microsoft.com/technet/security/notify.asp. For
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Microsoft Security Advisor web site at http://www.microsoft.com/security.