Microsoft Security Bulletin (MS00-080)
Patch Available for "Session ID Cookie Marking" Vulnerability
Originally posted: October 23, 2000
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
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
- IIS 4.0:
- IIS 5.0:
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.
- 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
Please see the following references for more information related to
- Frequently Asked Questions: Microsoft Security Bulletin MS00-080,
- Microsoft Knowledge Base article Q274149 discusses this issue
and will be available soon.
- RFC 2109, HTTP State Management,
- Microsoft TechNet Security web site,
Obtaining Support on this Issue
This is a fully supported patch. Information on contacting Microsoft
Product Support Services is available at
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.
- October 23, 2000: 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.
Last Updated October 23, 2000