From secnotif@MICROSOFT.COM Wed Sep 29 00:59:04 1999 From: Microsoft Product Security Resent-From: mea culpa To: MICROSOFT_SECURITY@ANNOUNCE.MICROSOFT.COM Resent-To: jericho@attrition.org Date: Tue, 28 Sep 1999 18:40:43 -0700 Subject: Microsoft Security Bulletin (MS99-040) The following is a Security Bulletin from the Microsoft Product Security Notification Service. Please do not reply to this message, as it was sent from an unattended mailbox. ******************************** Microsoft Security Bulletin (MS99-040) ====================================== Workaround for IE 5 "Download Behavior" Originally Posted: September 28, 1999 Summary ------- Microsoft has learned of a vulnerability in Microsoft® Internet Explorer 5 that could allow a malicious web site operator to take inappropriate action on the computer of a person who visited the site. Customers can immediately protect themselves against this vulnerability by disabling Active Scripting in IE 5, as discussed in the FAQ. Microsoft is also developing a patch that will restore safe operation to the affected feature; when the patch is available, this bulletin will be re-released. Additional information and frequently asked questions regarding this vulnerability can be found at http://www.microsoft.com/security/bulletins/MS99-040faq.asp Issue ----- IE 5 includes a feature called "download behavior" that allows web page authors to download files for use in client-side script. By design, a web site should only be able to download files that reside in its domain; this prevents client-side code from exposing files on the user's machine or local intranet to the web site. However, a server-side redirect can be used to bypass this restriction, thereby enabling a malicious web site operator to read files on the user's machine or the user's local intranet. This vulnerability would chiefly affect workstations that are connected to the Internet. As an immediate measure, customers can prevent the download behavior function from operating by disabling Active Scripting, as discussed in the FAQ. A patch that restores correct operation is under development and will be delivered shortly. Affected Software Versions ========================== - Microsoft Internet Explorer 5 Workaround ========== The vulnerability can be prevented by disabling Active Scripting. The FAQ contains details on how to do this. More Information ================ Please see the following references for more information related to this issue. - Microsoft Security Bulletin MS99-040: Frequently Asked Questions, http://www.microsoft.com/security/bulletins/ms99-040faq.asp. - Microsoft Knowledge Base (KB) article Q242542 Workaround available for download behavior vulnerability, http://support.microsoft.com/support/kb/articles/Q242/5/42.asp. (Note: It may take 24 hours from the posting of this bulletin for the KB article to appear) - Microsoft Security Advisor web site, http://www.microsoft.com/security/default.asp. Obtaining Support on this Issue =============================== Information on contacting Microsoft Technical Support is available at http://support.microsoft.com/support/contact/default.asp. Acknowledgments =============== Microsoft acknowledges Georgi Guninski for bringing this issue to our attention. Revisions ========= - September 28, 1999: Bulletin Created. ----------------------------------------------------------------------- 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/services/bulletin.asp. For security-related information about Microsoft products, please visit the Microsoft Security Advisor web site at http://www.microsoft.com/security.