J-048: Malformed HTR Request Vulnerability

PROBLEM:       A vulnerability has been identified in Microsoft® Internet
               Information Server (IIS) 4.0.
PLATFORM:      Windows NT 4 running IIS 4.0.  
DAMAGE:        This vulnerability could allow denial of service attacks, or
               under certain conditions, allow arbitrary code to be run. 
SOLUTION:      Apply workaround or patch.  
VULNERABILITY  Risk is high.  The exploit for this vulnerability has been 
ASSESSMENT:    publicly released. Apply workaround or patch immediately. 

[  UPDATED June 18, 1999 with patch information from Microsoft  ]

[  Start Microsoft Advisories  ]

Microsoft Security Bulletin (MS99-019)
--------------------------------------

Workaround Available for "Malformed HTR Request" Vulnerability

Originally Posted: June 15, 1999

Summary
=======
Microsoft has released a patch that eliminates a vulnerability in Microsoft
(r) Internet Information Server 4.0. The vulnerability could allow denial
of service attacks against an IIS server or, under certain conditions,
could allow arbitrary code to be run on the server.

Microsoft has issued this bulletin to advise customers of steps they can
take to protect themselves against this vulnerability. A patch to eliminate
this vulnerability is being developed, and an update to this bulletin will
be released to advise customers when it is available.

Issue
=====
IIS supports several file types that require server-side processing. When a
web site visitor requests a file of one of these types, an appropriate
filter DLL processes it. A vulnerability  exists in ISM.DLL, the filter DLL
that processes .HTR files. HTR files enable remote administration of user
passwords.

The vulnerability involves an unchecked buffer in ISM.DLL. This poses two
threats to safe operation. The first is a denial of service threat. A
malformed request for an .HTR file could  overflow the buffer, causing IIS
to crash. The server would not need to be rebooted, but IIS  would need to
be restarted. The second threat would be more difficult to exploit. A
carefully-constructed file request could cause arbitrary code to execute on
the server via a classic buffer overrun technique. Neither scenario could
occur accidentally. This vulnerability does not involve the functionality
of the password administration features of .HTR files.

While there are no reports of customers being adversely affected by this
vulnerability, Microsoft is proactively releasing this bulletin to allow
customers to take appropriate action to protect themselves against it.

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

What Microsoft is Doing
=======================
Microsoft has provided a workaround that fixes the problem identified. The
workaround is discussed below in What Customers Should Do.

Microsoft also has sent this security bulletin to customers
subscribing to the Microsoft Product Security Notification Service.
See http://www.microsoft.com/security/services/bulletin.asp for more
information about this free customer service.

What Customers Should Do
========================
Microsoft highly recommends that customers disable the script mapping for
.HTR files as follows:
 - From the desktop, start the Internet Service Manager
   by clicking Start | Programs | Windows NT 4.0 Option
   Pack | Microsoft Internet Information Server | Internet
   Service Manager
 - Double-click "Internet Information Server"
 - Right-click on the computer name and select Properties
 - In the Master Properties drop-down box, select "WWW Service",
   then click the "Edit" button .
 - Click the "Home Directory" tab, then click the "Configuration"
   button .
 - Highlight the line in the extension mappings that contains ".HTR",
   then click the "Remove" button.
 - Respond "yes" to "Remove selected script mapping?" say yes,
   click OK 3 times, close ISM

A patch will be available shortly to eliminate the vulnerability altogether.

Customers should monitor http://www.microsoft.com/security for an
announcement when the patches are available.

Microsoft recommends that customers review the IIS Security Checklist at
http://www.microsoft.com/security/products/iis/CheckList.asp

More Information
================
Please see the following references for more information related to this
issue.
 - Microsoft Security Bulletin MS99-019,
   Workaround Available for "Malformed HTR Request" Vulnerability
   (The Web-posted version of this bulletin),
   http://www.microsoft.com/security/bulletins/ms99-019.asp.
 - IIS Security Checklist,
   http://www.microsoft.com/security/products/iis/CheckList.asp

Obtaining Support on this Issue
===============================
If you require technical assistance with this issue, please contact
Microsoft Technical Support. For information on contacting Microsoft
Technical Support, please see
http://support.microsoft.com/support/contact/default.asp.

Revisions
=========
 - June 15, 1999: Bulletin Created.



For additional security-related information about Microsoft products,
please visit http://www.microsoft.com/security


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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.

(c) 1999 Microsoft Corporation. All rights reserved. Terms of Use.

   *******************************************************************
You have received  this e-mail bulletin as a result  of your registration
to  the   Microsoft  Product  Security  Notification   Service.  You  may
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and can be anything you like.

For  more  information on  the  Microsoft  Security Notification  Service
please    visit    http://www.microsoft.com/security/bulletin.htm.    For
security-related information  about Microsoft products, please  visit the
Microsoft Security Advisor web site at http://www.microsoft.com/security.

[  End Microsoft Advisory  ]

[  Append with Updated Microsoft Advisory  ]

Microsoft Security Bulletin (MS99-019)
--------------------------------------

Patch Available for "Malformed HTR Request" Vulnerability

Originally Posted: June 15, 1999
Updated: June 17, 1999

Summary
=======
This is an update to Microsoft Security Bulletin MS99-019. The purpose of
the update is to advise customers of the availability of a patch that
eliminates the vulnerability originally discussed, as well as variants that
Microsoft has subsequently identified.

Microsoft has released a patch that eliminates a vulnerability in
Microsoft(r) Internet Information Server 4.0. The vulnerability could allow
denial of service attacks against an IIS server or, under certain
conditions, could allow arbitrary code to be run on the server. The patch
is fully supported, and Microsoft recommends that affected customers
download and install it, if appropriate.

Issue
=====
IIS supports several file types that require server-side processing. When a
web site visitor requests a file of one of these types, an appropriate
filter DLL processes it. A vulnerability exists in the way that .HTR, .STM
and .IDC files are processed.

The vulnerability involves an unchecked buffer in the filter DLLs for these
file types.  This poses two threats to safe operation. The first is a denial
of service threat. A malformed request for an .HTR, .STM or .IDC file could
overflow the buffer, causing IIS to crash. The server would not need to be
rebooted, but IIS would need to be rebooted in order to resume service. The
second threat is that a carefully-constructed file request could cause
arbitrary code to execute on the server via a classic buffer overrun
technique. Neither attack could occur accidentally.

While there are no reports of customers being adversely affected
by this vulnerability, Microsoft is proactively releasing this
patch to allow customers to take appropriate action to protect
themselves against it. In addition, web sites that do not require
these file types can disable them altogether, as discussed in
Microsoft's IIS Security Checklist
(http://www.microsoft.com/security/products/iis/CheckList.asp)

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

What Microsoft is Doing
=======================
Microsoft has released a patch that fixes the problem identified. The patch
is available for download from the site listed below in What Customers
Should Do.

Microsoft also has sent this security bulletin to customers
subscribing to the Microsoft Product Security Notification Service.
See http://www.microsoft.com/security/services/bulletin.asp for
more information about this free customer service.

Microsoft has published the following Knowledge Base (KB) article on this
issue:
 - Microsoft Knowledge Base (KB) article Q234905,
   An Improperly Formatted HTTP Request Can Cause The Inetinfo
   Process To Fail,
   http://support.microsoft.com/support/kb/articles/q234/9/05.asp
   (Note: It might take 24 hours from the original posting of this
   bulletin for the KB article to be visible in the Web-based
   Knowledge Base.)

What Customers Should Do
========================
Microsoft highly recommends that customers evaluate the degree of risk that
this vulnerability poses to their systems and determine whether to download
and install the patch. The patch can be found at:
ftp://ftp.microsoft.com/bussys/IIS/iis-public/fixes/usa/ext-fix/.

More Information
================
Please see the following references for more information related to this
issue.
 - Microsoft Security Bulletin MS99-019,
   Patch Available for "Malformed HTR Request" Vulnerability,
   (The Web-posted version of this bulletin),
   http://www.microsoft.com/security/bulletins/ms99-019.asp.
 - Microsoft Knowledge Base (KB) article Q234905,
   An Improperly Formatted HTTP Request Can Cause The Inetinfo
   Process To Fail,
   http://support.microsoft.com/support/kb/articles/q234/9/05.asp.
 - IIS Security Checklist,
   http://www.microsoft.com/security/products/iis/CheckList.asp

Obtaining Support on this Issue
===============================
If you require technical assistance with this issue, please contact
Microsoft Technical Support. For information on contacting Microsoft
Technical Support, please see
http://support.microsoft.com/support/contact/default.asp.

Revisions
=========
 - June 15, 1999: Bulletin Created.
 - June 17, 1999: Bulletin updated to advise availability of patch
   for .HTR, .STM, and .IDC files


For additional security-related information about Microsoft products,
please visit http://www.microsoft.com/security


------------------------------------------------------------------------

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.

(c) 1999 Microsoft Corporation. All rights reserved. Terms of Use.

   *******************************************************************
You have received  this e-mail bulletin as a result  of your registration
to  the   Microsoft  Product  Security  Notification   Service.  You  may
unsubscribe from this e-mail notification  service at any time by sending
an  e-mail  to  MICROSOFT_SECURITY-SIGNOFF-REQUEST@ANNOUNCE.MICROSOFT.COM
The subject line and message body are not used in processing the request,
and can be anything you like.

For  more  information on  the  Microsoft  Security Notification  Service
please    visit    http://www.microsoft.com/security/bulletin.htm.    For
security-related information  about Microsoft products, please  visit the
Microsoft Security Advisor web site at http://www.microsoft.com/security.


[  End Updated Microsoft Advisory  ]

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