From secnotif@MICROSOFT.COM Tue Nov 21 14:39:09 2000 From: Microsoft Product Security To: BUGTRAQ@SECURITYFOCUS.COM Date: Mon, 20 Nov 2000 17:32:33 -0800 Subject: [BUGTRAQ] Microsoft Security Bulletin (MS00-080) The following is a Security Bulletin from the Microsoft Product Security Notification Service. Please do not reply to this message, as it was sent from an unattended mailbox. ******************************** -----BEGIN PGP SIGNED MESSAGE----- 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. 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