L-010: Microsoft IIS "Cookie Marking" Vulnerability

PROBLEM:       Microsoft IIS 4 and 5 web servers do not implement secure
               cookies for secure session management.
PLATFORM:      Microsoft IIS 4 or 5 web servers utilizing active server pages
               and that have both secure (https) and non-secure (http) web
               pages.
DAMAGE:        An intruder with full control of the communications channel
               between a web browser and a web server serving secure web pages
               can hijack the user's session.
SOLUTION:      Users with affected systems should install the patch and then
               implement secure cookies in their active server page
               application.
VULNERABILITY  Risk is LOW. The intruder must have complete control of the
ASSESSMENT:    communications channel between the web browser and the web
               server.


[****** Start of Microsoft Security Bulletin ******]

Microsoft Security Bulletin (MS00-080)
---------------------------------------

Patch Available for "Session ID Cookie Marking" Vulnerability

Originally posted: October 23, 2000

Summary
=======
Microsoft has released 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.

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).

Affected Software Versions
==========================
 - Microsoft Internet Information Server 4.0
 - Microsoft Internet Information Services 5.0

Patch Availability
==================
 - IIS 4.0:
   http://www.microsoft.com/Downloads/Release.asp?ReleaseID=25233
 - IIS 5.0:
   http://www.microsoft.com/Downloads/Release.asp?ReleaseID=25232

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(r) 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(r) 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.

[****** End of Microsoft Security Bulletin ******]

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