Improperly Formatted HTTP Request May Cause INETINFO Process to Fail

ID: Q234905

The information in this article applies to:

Microsoft Internet Information Server version 4.0

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:

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

Right-click the computer name and then click Properties.

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

Click the Home Directory tab, and then click Configuration.

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

Select the Check if file exists check box.

Repeat these steps for the STM and IDC application mappings.

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

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/

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://www.microsoft.com/support/supportnet/overview/overview.asp

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/

STATUS

Microsoft has confirmed this to be a problem in Internet Information Server 4.0. This problem was first corrected in Windows NT 4.0 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 : NT4SP6Fix
Version : winnt:4.0
Platform : winnt
Issue type : kbbug