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IIS Denial of Service and File Reading Vulnerabilities



Denial of Service and File Reading Vulnerabilities Privacy and Legal Notice

CIAC

K-041: Denial of Service and File Reading Vulnerabilities in Microsoft IIS

May 16, 2000 18:00 GMT


PROBLEM:       Microsoft has identified two Denial of Service vulnerabilities
               and one file reading vulnerability in Microsoft(r) Internet
               Information Server (IIS).
PLATFORM:      Platforms running Microsoft IIS 4.0 and 5.0.
DAMAGE:        (1) Denial of Service vulnerabilities may be used to slow the
               affected web server's responses to it users. (2) The file
               reading vulnerability could allow unauthorized disclosure of
               fragments of certain types of files.
SOLUTION:      Apply the vendor's patches as directed by the advisories.


VULNERABILITY The risk is LOW. The vulnerabilities have been discussed in ASSESSMENT: public forums. However, none of these vulnerabilities would allow data to be changed, added or deleted on the server, nor would they allow administrative control over the machine to be usurped.


This CIAC bulletin contains Microsoft Security Bulletins MS00-030 and MS00-
031.

[ Start of Microsoft Security Bulletin MS00-030 ]

Microsoft Security Bulletin (MS00-030)
- - --------------------------------------

Patch Available for "Malformed Extension Data in URL" Vulnerability

Originally Posted: May 11, 2000

Summary
=======
Microsoft has released a patch that eliminates a security
vulnerability in Microsoft(r) Internet Information Server. The
vulnerability could be used to slow the performance of an affected
server, or temporarily stop it altogether.

Frequently asked questions regarding this vulnerability and
the patch can be found at
http://www.microsoft.com/technet/security/bulletin/fq00-030.asp

Issue
=====
In compliance with RFC 2396, the algorithm in IIS that processes URLs
has flexibility built in to allow it to process any  arbitrary
sequence of file extensions or subresource identifiers (referred to in
the RFC as path_segments). By providing an  URL that contains
specially-malformed file extension information, a malicious user could
misuse this flexibility in order to  arbitrarily increase the work
factor associated with parsing the URL. This could consume much or all
of the CPU availability  on the server and prevent useful work from
being done.

The vulnerability does not provide any capability to cause the server
to fail, or to add, change or delete data on it.  Likewise, it
provides no capability to usurp administrative control of the web
server. The slowdown would only last until the  URL had been
processed, at which point service would return to normal.

Affected Software Versions
==========================
 - Microsoft Internet Information Server 4.0
 - Microsoft Internet Information Server 5.0

Patch Availability
==================
 - Internet Information Server 4.0:
   http://www.microsoft.com/Downloads/Release.asp?ReleaseID=20906
 - Internet Information Server 5.0:
   http://www.microsoft.com/Downloads/Release.asp?ReleaseID=20904

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 MS00-030,
   http://www.microsoft.com/technet/security/bulletin/fq00-030.asp
 - Microsoft Knowledge Base article Q260205 discusses this issue
   and will be available soon.
 - RFC 2396, Uniform Resource Identifiers (URI): Generic Syntax,
   http://www.ietf.org/rfc/rfc2396.txt.
 - 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 Underground Security Systems Research
(http://www.ussrback.com) for reporting this vulnerability to us and
working with us to protect customers.

Revisions
=========
 - May 11, 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 11, 2000

(c) 2000 Microsoft Corporation. All rights reserved. Terms of use.

[ End of Microsoft Security Bulletin MS00-030 ]


[ Start of Microsoft Security Bulletin MS00-031 ]

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.

 [ End of Microsoft Security Bulletin MS00-031 ]


CIAC wishes to acknowledge the contributions of Microsoft for the information contained in this bulletin.



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