Microsoft Security Bulletin (MS99-053)

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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.

------------------------------------------------------------------------

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