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Microsoft Security Bulletin (MS00-080)

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



Patch Available for "Session ID Cookie Marking" Vulnerability



Originally posted: October 23, 2000

Updated: November 20, 2000



Summary

=======

On October 23, 2000, Microsoft released the original version of this

bulletin, to discuss the availability of a patch that eliminates a

security vulnerability in Microsoft(r) Internet Information Server.

The vulnerability could allow a malicious user to "hijack" another

user's secure web session, under a very restricted set of

circumstances.



On November 20, 2000, we re-released the bulletin to advise customers

using IIS 4.0 on Alpha platforms, or IIS 5.0 on x86 platforms, that

new versions of these patch are available, to correct an error in the

original version of the patch. The x86 IIS 4.0 patch was not affected

by the error, and customers using these systems do not need to take

any action.



Frequently asked questions regarding this vulnerability and

the patch can be found at

http://www.microsoft.com/technet/security/bulletin/fq00-080.asp



Issue

=====

IIS supports the use of a Session ID cookie to track the current

session identifier for a web session. However, .ASP in IIS does not

support the creation of secure Session ID cookies as defined in RFC

2109. As a result, secure and non-secure pages on the same web site

use the same Session ID. If a user initiated a session with a secure

web page, a Session ID cookie would be generated and sent to the

user, protected by SSL. But if the user subsequently visited a

non-secure page on the same site, the same Session ID cookie would be

exchanged, this time in plaintext. If a malicious user had complete

control over the communications channel, he could read the plaintext

Session ID cookie and use it to connect to the user's session with

the secure page. At that point, he could take any action on the

secure page that the user could take.



The conditions under which this vulnerability could be exploited are

rather daunting. The malicious user would need to have complete

control over the other user's communications with the web site. Even

then, the malicious user could not make the initial connection to the

secure page - only the legitimate user could do that. The patch

eliminates the vulnerability by adding support for secure Session ID

cookies in .ASP pages. (Secure cookies already are supported for all

other types of cookies, under all other technologies in IIS).



The original version of patches for IIS 4.0 Alpha and the IIS 5.0

systems did not install correctly. The IIS 4.0 x86 version of the

patch does install correctly.



Affected Software Versions

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

 - Microsoft Internet Information Server 4.0

 - Microsoft Internet Information Services 5.0



Patch Availability

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

 - IIS 4.0:

   x86 platforms:

   http://www.microsoft.com/ntserver/nts/downloads/critical/q274149

   Alpha platforms:

   Available from Microsoft Product Support Services

 - IIS 5.0:

   http://www.microsoft.com/Windows2000/downloads/critical/q274149



Note: The patch installs support for secure Session ID cookies, but

does not enable it for reasons of application compatibility. As

discussed in the Knowledge Base article, it can be enabled or

disabled on a site-by-site basis.



Note:

 - The IIS 4.0 version of this patch can be installed on Windows

   NT 4.0 systems running Service Pack 6a, and will be included

   in Service Pack 7.

 - The IIS 5.0 version of this patch can be installed on Windows

   2000 systems with or without Service Pack 1, and will be

   included in Service Pack 2.



Note: Additional security patches are available at the Microsoft

Download Center



More Information

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

Please see the following references for more information related to

this issue.

 - Frequently Asked Questions: Microsoft Security Bulletin MS00-080,

   http://www.microsoft.com/technet/security/bulletin/fq00-080.asp

 - Microsoft Knowledge Base article Q274149 discusses this issue

   and will be available soon.

 - RFC 2109, HTTP State Management,

   http://www.ietf.org/rfc/rfc2109.txt.

 - Microsoft TechNet Security web site,

   http://www.microsoft.com/technet/security/default.asp



Obtaining Support on this Issue

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

This is a fully supported patch. Information on contacting Microsoft

Product Support Services is available at

http://support.microsoft.com/support/contact/default.asp.



Acknowledgments

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

Microsoft thanks ACROS Security (http://www.acros.si/) and Ron Sires

and C. Conrad Cady of Healinx (http://www.healinx.com/) for reporting

this issue to us and working with us to protect customers.



Revisions

=========

 - October 23, 2000: Bulletin Created.

 - November 20, 2000: Bulletin updated to indicate availability of

   updated patches for IIS 4.0 on Alpha platforms, and IIS 5.0

   on x86 platforms.



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



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.





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