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Microsoft Security Bulletin (MS99-035)

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



Patch Available for "Set Cookie Header Caching" Vulnerability

Originally Posted: September 10, 1999



Summary

=======

Microsoft has released a patch that eliminates a vulnerability in

Microsoft(r) Site Server(r) and Microsoft Commercial Internet System(r)

(MCIS). The vulnerability could allow a web site visitor to inadvertently

access another customer's data, if their Internet gateway caches web pages

via a proxy server and the web site authenticates based on a GUID.



Frequently asked questions regarding this vulnerability can be found

at http://www.microsoft.com/security/bulletins/MS99-035faq.asp



Issue

=====

When certain versions of Site Server or MCIS send a web page that contains a

Set Cookie Header, they do not flag the page with an expiration header. As a

result, such pages may be cached by a web proxy. Multiple customers

accessing the same site via a web proxy might be served the same page,

containing the same Set Cookie Header. If the cookie information includes a

GUID that is used as an index for the server's database, one customer's

personal data might be viewable by the others.



When GUIDs are issued to new clients as part of the authentication process,

they can be presumed to be unique. However, they cannot be presumed to be

secret. The patch eliminates the specific vulnerability at hand, but other

attacks are possible whenever authentication is based solely on information

contained in cookies. Sites that follow security best practices, such as

turning off automatic cookie authentication, would not be affected by this

vulnerability.



Affected Software Versions

==========================

 - Microsoft Site Server 3.0

 - Microsoft Site Server 3.0 Commerce Edition

 - Microsoft Commercial Internet System 2.0 and 2.5



Patch Availability

==================

 - ftp://ftp.microsoft.com/bussys/sitesrv/sitesrv-public/

   fixes/usa/siteserver3/Hotfixes-PostSP2/ProxyCache/



   NOTE: Line breaks have been inserted into the above URL for readability



More Information

================

Please see the following references for more information related to this

issue.

 - Microsoft Security Bulletin MS99-035: Frequently Asked Questions,

   http://www.microsoft.com/security/bulletins/MS99-035faq.asp.

 - Microsoft Knowledge Base (KB) article Q238647,

   Proxy Caching Can Cause Multiple Clients to Receive the Same GUID,

   http://support.microsoft.com/support/kb/articles/q238/6/47.asp.

   (Note: It may take 24 hours from the original posting of this

   bulletin for the 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.



Revisions

=========

 - September 10, 1999: Bulletin Created.



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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.



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