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Q234905: Improperly Formatted HTTP Request May Cause INETINFO to Fail

Article: Q234905
Product(s): Internet Information Server
Version(s): winnt:4.0
Operating System(s): 
Keyword(s): kbWinNT4sp6fix
Last Modified: 20-MAY-2002

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The information in this article applies to:

- Microsoft Windows NT Server version 4.0, Terminal Server Edition 
- Microsoft Internet Information Server version 4.0 
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SYMPTOMS
========

When a Web site visitor requests a selected file mapping, the request is mapped
to an appropriate DLL for processing the visitor's request. The appropriate DLL
may include any Microsoft DLL or an installed third-party filter DLL. A problem
currently exists in the Microsoft DLLs for handling an improperly formatted
request that uses an HTR, STM, or IDC application mapping. There is the
possibility that this problem could be exploited by a malicious Web user by
sending an improperly formatted HTTP request to a Microsoft Internet Information
Server (IIS) computer, which can result in the unstable operation of the Web
server.

WORKAROUND
==========

Microsoft has provided a patch to correct this problem; however, additional
steps can be used to prevent issues similar to this one from impacting any
Microsoft IIS 4.0 computer. Selecting Check if file Exists in the script
application mappings section of the ISM forces IIS 4.0 to check if the requested
script exists or if the user has permission to the requested script. If not, the
appropriate warning message is returned to the browser and the script engine is
not invoked.

To select Check if file Exists, perform the following steps:

1. In the Internet Service Manager (ISM), double-click Internet Information
  Server.

2. Right-click the computer name and then click Properties.

3. In the Master Properties drop-down box, click WWW Service, and then click
  Edit.

4. Click the Home Directory tab, and then click Configuration.

5. Double-click the line in the extension mappings that contains .HTR.

6. Select the Check if file exists check box.

7. Repeat these steps for the STM and IDC application mappings.

8. Close the ISM.

NOTE: When you choose to use this option, the originating TCP\IP address of the
request and the response is logged in the IIS log if IIS logging is turned on.

RESOLUTION
==========

Windows NT Server or Workstation 4.0
------------------------------------

To resolve this problem, obtain the latest service pack for Windows NT 4.0 or the
individual software update. For information on obtaining the latest service
pack, please go to:

- http://www.microsoft.com/Windows/ServicePacks/

-or-

- Q152734 How to Obtain the Latest Windows NT 4.0 Service Pack

For information on obtaining the individual software update, contact Microsoft
Product Support Services. For a complete list of Microsoft Product Support
Services phone numbers and information on support costs, please go to the
following address on the World Wide Web:

  http://support.microsoft.com/default.aspx?scid=fh;EN-US;CNTACTMS


Windows NT Server 4.0, Terminal Server Edition
----------------------------------------------

To resolve this problem, obtain the latest service pack for Windows NT Server
4.0, Terminal Server Edition. For additional information, please see the
following article in the Microsoft Knowledge Base:

  Q152734 How to Obtain the Latest Windows NT 4.0 Service Pack


STATUS
======

Microsoft has confirmed this to be a problem in Windows NT 4.0 and Windows NT
Server 4.0, Terminal Server Edition.

This problem was first corrected in Windows NT Server 4.0 Service Pack 6 and
Windows NT Server 4.0, Terminal Server Edition Service Pack 6.

MORE INFORMATION
================

The effected application mappings are IDC, HTR, and STM.

- HTR files enable remote administration of user passwords.

- IDC Internet Database Connector files allows an Internet application to query
  and update backend database.

- STM is used for server-side Include files.

Please see the following Microsoft Security Bulletin (MS99-019) for more
information related to this issue:

  Patch Available for "Malformed HTR Request" Vulnerability

For additional security-related information about Microsoft products, please
visit:

  http://www.microsoft.com/security

Additional query words:

======================================================================
Keywords          : kbWinNT4sp6fix 
Technology        : kbWinNTsearch kbWinNT400search kbWinNTSsearch kbWinNTS400search kbNTTermServ400 kbNTTermServSearch kbiisSearch kbiis400
Version           : winnt:4.0
Hardware          : ALPHA x86
Issue type        : kbbug
Solution Type     : kbfix

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