DOCUMENT:Q234905 TITLE :An Improperly Formatted HTTP Request Can Cause the INETINFO Process to Fail PRODUCT :IIS PROD/VER:4.0 OPER/SYS:WINDOWS NT KEYWORD :prodiis4 -------------------------------------------------------------------------------- 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, this request is mapped to an appropriate DLL for processing the web site visitor request. The appropriate DLL may include any shipping Microsoft DLL or an installed third-party filter DLL. A problem currently exists in the shipping Microsoft DLL's 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 computer which can result in the unstable operation of the web server. 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 4.0 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://support.microsoft.com/support/supportnet/default.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 affected 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 are used for Server side include files 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 Server. 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. Perform the following steps to select "Check if file Exists": 1. In Internet Service Manager (ISM), double-click Internet Information Server. 2. Right-click the computer name and then click Properties on the menu that appears. 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 checkbox labeled "Check if file exists". 7. Repeat these steps for STM and IDC application mappings. 8. Close the ISM. NOTE: When selecting 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. MORE INFORMATION ================ Please see the following reference for more information related to this issue: Microsoft Security Bulletin MS99-019, "Patch Available for "Malformed HTR Request" Vulnerability": http://www.microsoft.com/security/bulletins/ms99-019.asp 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. 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