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 until patch is available.
VULNERABILITY Risk is high. The exploit for this vulnerability has been ASSESSMENT: publicly released. Apply workaround immediately.
[ 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 ------------------------------------------------------------------ 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 Microsoft Advisories ]
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