__________________________________________________________ The U.S. Department of Energy Computer Incident Advisory Center ___ __ __ _ ___ / | /_\ / \___ __|__ / \ \___ __________________________________________________________ INFORMATION BULLETIN Microsoft Exchange Server Outlook Web Access Flaw [Microsoft Security Bulletin MS01-030, Version 3] [Revision A 6/20/2001 Used Version 3] June 20, 2001 17:00 GMT Number L-091A ______________________________________________________________________________ PROBLEM: A flaw exists in the interaction between Outlook Web Access (OWA) and Internet Explorer for message attachments. An attachment containing html code, including script, could execute when the attachment is opened regardless of the attachment type. PLATFORM: Microsoft Exchange 2000 and Exchange 5.5 DAMAGE: The flaw could execute script contained in an attachment. An attacker could construct an attachment containing malicious code, which would execute if the user opened it. SOLUTION: Apply the patches as described below. ______________________________________________________________________________ VULNERABILITY The risk is LOW: The vulnerability is only exploitable by ASSESSMENT: attachments that are received through OWA. It still requires the user to open an attachment. Users should know not to open unexpected attachments from any source. ______________________________________________________________________________ [****** Start Microsoft Advisory ******] ---------------------------------------------------------------------- Title: Incorrect Attachment Handling in Exchange OWA Can Execute Script Date: 06 June 2001 Revised: 13 June 2001 (version 3.0) Software: Exchange 5.5, Exchange 2000 Impact: Run code of attacker's choice on mail client Bulletin: MS01-030 Microsoft encourages customers to review the Security Bulletin at: http://www.microsoft.com/technet/security/bulletin/MS01-030.asp. ---------------------------------------------------------------------- Reason for Revision: ==================== On June 12, 2001 Microsoft discovered that the updated Exchange 2000 patch contained outdated files. We have corrected the error and provided an updated version of this patch for Exchange 2000. We recommend that all customers who have downloaded the Exchange 2000 patch prior to June 12, 2001 install the updated version. Issue: ====== OWA is a service of Exchange Server that allows users to use a web browser to access their Exchange mailbox. However, a flaw exists in the interaction between OWA and IE for message attachments. If an attachment contains HTML code including script, the script will be executed when the attachment is opened, regardless of the attachment type. Because OWA requires that scripting be enabled in the zone where the OWA server is located, this script could take action against the user's Exchange mailbox. An attacker could use this flaw to construct an attachment containing malicious script code. The attacker could then send the attachment in a message to the user. If the user opened the attachment in OWA, the script would execute and could take action against the user's mailbox as if it were the user, including, under certain circumstances, manipulation of messages or folders. Mitigating Factors: ==================== - The vulnerability could only be exploited if the user were using OWA in conjunction with IE. - The vulnerability is only exploitable by attachments that are received via OWA. In general, an attacker would have no way to determine whether a user would open an attachment using OWA rather than an Outlook client. - An attacker's ability to exploit this vulnerability would require that she entice the user to open an attachment from an untrusted source. Best practices recommend against opening any attachment from an unknown or untrusted source. Patch Availability: =================== - A patch is available to fix this vulnerability. Please read the Security Bulletin http://www.microsoft.com/technet/security/bulletin/ms01-030.asp for information on obtaining this patch. Acknowledgment: =============== - Joao Gouveia (tharbad@kaotik.org) --------------------------------------------------------------------- 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 Microsoft Advisory ******] _______________________________________________________________________________ CIAC wishes to acknowledge the contributions of Microsoft for the information contained in this bulletin. _______________________________________________________________________________ CIAC, the Computer Incident Advisory Center, 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/ Anonymous FTP: ftp.ciac.org 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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