Improperly Formatted HTTP Request May Cause INETINFO Process to Fail

ID: Q234905

The information in this article applies to:

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

A supported fix that corrects this problem is now available from Microsoft, but it has not been fully regression tested and should be applied only to systems experiencing this specific problem. If you are not severely affected by this specific problem, Microsoft recommends that you wait for the next Windows NT service pack that contains this fix.

To resolve this problem immediately, contact Microsoft Product Support Services to obtain the fix. 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://www.microsoft.com/support/supportnet/overview/overview.asp
The English version of this fix should have the following file attributes or later:

   Date       Time                Size    File name     Platform
   -------------------------------------------------------------
   06-09-1999 6:51:10PM           53,504  Ism.dll       x86
   06-09-1999 6:36:02PM           82,704  Ism.dll       Alpha
This hotfix has been posted to the following Internet location as Extfixi.exe (x86) and Extfixa.exe (Alpha):
ftp://ftp.microsoft.com/bussys/IIS/iis-public/fixes/usa/ext-fix/

NOTE: If this product was already installed on your computer when you purchased it from the Original Equipment Manufacturer (OEM) and you need this fix, please call the Pay Per Incident number listed on the above Web site. If you contact Microsoft to obtain this fix, and if it is determined that you only require the fix you requested, no fee will be charged. However, if you request additional technical support, and if your no-charge technical support period has expired, or if you are not eligible for standard no-charge technical support, you may be charged a non-refundable fee.

For more information about eligibility for no-charge technical support, see the following article in the Microsoft Knowledge Base:
Q154871 Determining If You Are Eligible for No-Charge Technical Support


STATUS

Microsoft has confirmed this to be a problem in Internet Information Server 4.0.


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          : 
Version           : winnt:4.0
Platform          : winnt 
Issue type        : kbbug

    Last Reviewed: July 2, 1999