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Microsoft IIS "Cookie Marking" Vulnerability
Microsoft IIS "Cookie Marking" Vulnerability Privacy and Legal Notice


L-010: Microsoft IIS "Cookie Marking" Vulnerability

October 24, 2000 18:00 GMT
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
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

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 ******]

CIAC wishes to acknowledge the contributions of Microsoft for the information contained in this bulletin.
CIAC services are available to DOE, DOE Contractors, and the NIH. CIAC can be contacted at:
    Voice:          +1 925-422-8193 (7 x 24)
    FAX:            +1 925-423-8002
    STU-III:        +1 925-423-2604
    E-mail:          ciac@llnl.gov
    World Wide Web:  http://www.ciac.org/
                     (same machine -- either one will work)
    Anonymous FTP:   ftp.ciac.org
                     (same machine -- either one will work)

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