The U.S. Department of Energy Computer Incident Advisory Capability ___ __ __ _ ___ / | /_\ / \___ __|__ / \ \___ __________________________________________________________ INFORMATION BULLETIN Microsoft IIS and Exchange Malformed URL Denial of Service March 2, 2001 18:00 GMT Number L-054 ______________________________________________________________________________ PROBLEM: Malformed URL may cause a Denial of Servie in IIS 5.0 and Exchange 2000. PLATFORM: Microsoft IIS 5.0 and Exchange 2000 DAMAGE: If a malformed URL were repeatedly sent to an affected system, a confluence of events could cause a memory allocation error that would result in the failure of the service. SOLUTION: Install the patches as per Microsoft instructions. ______________________________________________________________________________ VULNERABILITY The risk is MEDIUM. Malformed URLs are easy to construct that ASSESSMENT: would cause the Denial of Service. ______________________________________________________________________________ [****** Start of Microsoft Security Bulletin ******] ----------------------------------------------------------------------- Title: Malformed URL can cause Service Failure in IIS 5.0 and Exchange 2000 Date: 01 March 2001 Software: IIS 5.0 and Exchange 2000 Impact: Denial of Service Bulletin: MS01-014 Microsoft encourages customers to review the Security Bulletin at: http://www.microsoft.com/technet/security/bulletin/MS01-014.asp. ----------------------------------------------------------------------- Issue: ====== IIS 5.0 contains a flaw affecting the way that an URL is handled if it has a specific construction and its length is within a very narrow range of values. If such an URL were repeatedly sent to an affected system, a confluence of events could cause a memory allocation error that would result in the failure of the IIS service. Exchange 2000 is affected by the same vulnerability. To support web-based mail clients, it introduces the ability to address items on the store via URLs. This is done in part by using IIS 5.0, and in part via code that is specific to Exchange 2000. Both pieces of code contain the flaw, but the effect of exploiting the vulnerability via either would be the same -- it could be used to cause the IIS service to fail, but could not be used to attack the Exchange service itself. That is, successfully attacking an Exchange server via this vulnerability would disrupt web-based mail clients' use of the server, but not that of MAPI-based mail clients like Outlook. Because the flaw occurs in two different code modules, one of which installs as part of IIS 5.0 and both of which install as part of Exchange 2000, it is important for Exchange 2000 administrators to install both the IIS and Exchange patches. Mitigating Factors: ==================== - The vulnerability would not enable the attacker to gain any administrative control over the server, or to alter any data on it. - The affected services automatically restart in the event of a failure, so an affected system would resume service almost immediately. - A successful attack against an Exchange server would only disrupt web-based mail clients' use of the server. The server would continue to be available for MAPI-based clients like Outlook. - The ISAPI involved in this vulnerability authenticates the user prior to servicing the request, so a properly configured Exchange server would be at less risk than an IIS server. Patch Availability: =================== - A patch is available to fix this vulnerability. Please read the Security Bulletin http://www.microsoft.com/technet/security/bulletin/ms01-014.asp for information on obtaining this patch. Acknowledgment: =============== - Kevin Kotas of eSecurityOnline.com (http://eSecurityOnline.com) ---------------------------------------------------------------------- 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. [****** End of Microsoft Security Bulletin ******] _______________________________________________________________________________ CIAC wishes to acknowledge the contributions of Microsoft for the information contained in this bulletin. _______________________________________________________________________________ CIAC, the Computer Incident Advisory Capability, is the computer security incident response team for the U.S. Department of Energy (DOE) and the emergency backup response team for the National Institutes of Health (NIH). CIAC is located at the Lawrence Livermore National Laboratory in Livermore, California. CIAC is also a founding member of FIRST, the Forum of Incident Response and Security Teams, a global organization established to foster cooperation and coordination among computer security teams worldwide. CIAC services are available to DOE, DOE contractors, and the NIH. CIAC can be contacted at: Voice: +1 925-422-8193 (7x24) FAX: +1 925-423-8002 STU-III: +1 925-423-2604 E-mail: ciac@ciac.org Previous CIAC notices, anti-virus software, and other information are available from the CIAC Computer Security Archive. World Wide Web: http://www.ciac.org/ (or http://ciac.llnl.gov -- they're the same machine) Anonymous FTP: ftp.ciac.org (or ciac.llnl.gov -- they're the same machine) PLEASE NOTE: Many users outside of the DOE, ESnet, and NIH computing communities receive CIAC bulletins. If you are not part of these communities, please contact your agency's response team to report incidents. Your agency's team will coordinate with CIAC. The Forum of Incident Response and Security Teams (FIRST) is a world-wide organization. A list of FIRST member organizations and their constituencies can be obtained via WWW at http://www.first.org/. This document was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor the University of California nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial products, process, or service by trade name, trademark, manufacturer, or otherwise, does not necessarily constitute or imply its endorsement, recommendation or favoring by the United States Government or the University of California. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or the University of California, and shall not be used for advertising or product endorsement purposes. 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