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 (MS99-053) -------------------------------------- Patch Available for Windows "Multithreaded SSL ISAPI Filter" Vulnerability Originally Posted: December 02, 1999 Summary ======= Microsoft has released a patch that eliminates a vulnerability in the SSL ISAPI filter that ships with Microsoft(r) Internet Information Server and is used by other Microsoft products. If called by a multi-threaded application under very specific, and fairly rare, circumstances, a synchronization error in the filter could allow a single buffer of plaintext to be transmitted back to the data's owner. Frequently asked questions regarding this vulnerability can be found at http://www.microsoft.com/security/bulletins/MS99-053faq.asp. Issue ===== The SSL ISAPI filter provided as part of IIS supports concurrent use. When used in this mode, a synchronization problem could induce a race condition and cause a single buffer of plaintext to be leaked. The conditions under which this could happen are very rare, and could only occur when a single user's session was multi-threaded and traffic volumes were extremely high. The scope of this vulnerability is very limited. The leaked plaintext would always be sent to its owner, never another user. Also, because the leaked data would fail its integrity check, the effect of the leak would be to cause the SSL session to immediately collapse. The condition could not be induced by a hostile user, and would offer at best a target of opportunity. Finally, it is worth noting that this vulnerability only affects the SSL ISAPI filter, not the secure communications capability provided by Windows NT via Schannel. Affected Software Versions ========================== - Microsoft IIS 4.0 - Microsoft Site Server 3.0 - Microsoft Site Server Commerce Edition 3.0 Patch Availability ================== - x86: http://www.microsoft.com/downloads/release.asp?ReleaseID=16186 - Alpha: http://www.microsoft.com/downloads/release.asp?ReleaseID=16187 NOTE: This and other patches are available from the Microsoft Download Center (http://www.microsoft.com/downloads/search.asp? Search=Keyword&Value='security_patch'&OpSysID=1) More Information ================ Please see the following references for more information related to this issue. - Microsoft Security Bulletin MS99-053: Frequently Asked Questions, http://www.microsoft.com/security/bulletins/MS99-053faq.asp. - Microsoft Knowledge Base (KB) article Q244613, IIS 4.0 SSL ISAPI Filter Can Leak Single Buffer of Plaintext, http://support.microsoft.com/support/kb/articles/q244/6/13.asp. (Note: It may take 24 hours from the original posting of this bulletin for this KB article to be visible.) - Microsoft Security Advisor web site, http://www.microsoft.com/security/default.asp. Obtaining Support on this Issue =============================== This is a fully supported patch. Information on contacting Microsoft Technical Support is available at http://support.microsoft.com/support/contact/default.asp. Acknowledgments =============== Microsoft acknowledges Wall Data for bringing this issue to our attention. Revisions ========= - December 02, 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-REQUESTat_private 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.
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