Microsoft Security Bulletin MS99-035 - Critical
Patch Available for "Set Cookie Header Caching" Vulnerability
Published: September 10, 1999 | Updated: March 21, 2003
Patch Availability Information Updated: March 21, 2003
Originally Posted: September 10, 1999
Microsoft has released a patch that eliminates a vulnerability in Microsoft® Site Server®and Microsoft Commercial Internet System® (MCIS). The vulnerability could allow a web site visitor to inadvertently access another customer's data, if their Internet gateway caches web pages via a proxy server and the web site authenticates based on a GUID.
Frequently asked questions regarding this vulnerability can be found at http://www.microsoft.com/technet/security/bulletin/fq99-035.mspx
When certain versions of Site Server or MCIS send a web page that contains a Set Cookie Header, they do not flag the page with an expiration header. As a result, such pages may be cached by a web proxy. Multiple customers accessing the same site via a web proxy might be served the same page, containing the same Set Cookie Header. If the cookie information includes a GUID that is used as an index for the server's database, one customer's personal data might be viewable by the others.
When GUIDs are issued to new clients as part of the authentication process, they can be presumed to be unique. However, they cannot be presumed to be secret. The patch eliminates the specific vulnerability at hand, but other attacks are possible whenever authentication is based solely on information contained in cookies. Sites that follow security best practices, such as turning off automatic cookie authentication, would not be affected by this vulnerability.
Affected Software Versions
- Microsoft Site Server 3.0
- Microsoft Site Server 3.0 Commerce Edition
- Microsoft Commercial Internet System 2.0 and 2.5
Vulnerability Identifier: CAN-1999-0910
Please see the following references for more information related to this issue.
- Microsoft Security Bulletin MS99-035: Frequently Asked Questions, http://www.microsoft.com/technet/security/bulletin/fq99-035.mspx.
Microsoft Knowledge Base (KB) article 238647, Proxy Caching Can Cause Multiple Clients to Receive the Same GUID, http://support.microsoft.com/default.aspx?scid=kb;en-us;238647&sd=tech.
Note It may take 24 hours from the original posting of this bulletin for the KB article to be visible.
Microsoft Security web site, http://www.microsoft.com/technet/security/default.mspx.
Obtaining Support on this Issue
This is a fully supported patch. Information on contacting Microsoft Technical Support is available at http://support.microsoft.com/contactussupport/?ws=support.
- September 10, 1999: Bulletin Created.
- V2.0 (March 21, 2003): Introduced versioning and updated patch availability information.
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