Microsoft Security Bulletin MS00-033

Patch Available for "Frame Domain Verification", "Unauthorized Cookie Access", and "Malformed Component Attribute" Vulnerabilities

Originally Posted: May 17, 2000

Summary

Microsoft has released a comprehensive patch that eliminates three security vulnerabilities in Microsoft® Internet Explorer 4 and 5:

The "Frame Domain Verification" vulnerability, which could allow a malicious web site operator to read, but not change or add, files on the computer of a visiting user.
The "Unauthorized Cookie Access" vulnerability, which could allow a malicious web site operator to access "cookies" belonging to a visiting user.
The "Malformed Component Attribute" vulnerability, which could allow a malicious web site operator to run code of his choice on the computer of a visiting user.

General Information

Issue

The three security vulnerabilities eliminated by this patch are unrelated to each other except by the fact that they all occur in the same .dll. We have packaged the fix for all three issues together in one updated .dll together for customer convenience. The vulnerabilities are:

"Frame Domain Verification" vulnerability. When a web server opens a frame within a window, the IE security model should only allow the parent window to access the data in the frame if they are in the same domain. However, two functions available in IE do not properly perform domain checking, with the result that the parent window could open a frame that contains a file on the local computer, then read it. This could allow a malicious web site operator to view files on the computer of a visiting user. The web site operator would need to know (or guess) the name and location of the file, and could only view file types that can be opened in a browser window.
"Unauthorized Cookie Access" vulnerability. By design, the IE security model restricts cookies so that they can be read only by sites within the originator's domain. However, by using a specially-malformed URL, it is possible for a malicious web site operator to gain access to another site's cookie and read, add or change them. A malicious web site operator would need to entice a visiting user into clicking a link in order to access each cookie, and could not obtain a listing of the cookies available on the visitor's system. Even after recovering a cookie, the type and amount of personal information would depend on the privacy practices followed by the site that place it there.
"Malformed Component Attribute" vulnerability. The code used to invoke ActiveX components in IE has an unchecked buffer and could be exploited by a malicious web site operator to run code on the computer of a visiting user. The unchecked buffer is only exposed when certain attributes are specified in conjunction with each other.

The patch also eliminates a new variant of the previously-addressed WPAD Spoofing vulnerability.

Affected Software Versions

Microsoft Internet Explorer 4.0
Microsoft Internet Explorer 4.01
Microsoft Internet Explorer 5.0
Microsoft Internet Explorer 5.01
Note: Microsoft Internet Explorer 5.5 and 5.01 Service Pack 1 are not affected by these vulnerabilities

Vulnerability Identifiers

Unauthorized Cookie Access Vulnerability: CVE-2000-0439
Malformed Component Attribute Vulnerability: CVE-2000-0464
Frame Domain Verification Vulnerability: CVE-2000-0465

Patch Availability

More Information

Please see the following references for more information related to this issue.

Frequently Asked Questions: Microsoft Security Bulletin MS00-033, http://www.microsoft.com/technet/security/bulletin/fq00-033.mspx
Microsoft Knowledge Base (KB) article 262509, http://support.microsoft.com/default.aspx?scid=kb;en-us;262509
Microsoft Knowledge Base (KB) article 251108, Update Available for the 'Frame Domain Verification' Issue, http://support.microsoft.com/default.aspx?scid=kb;en-us;251108
Microsoft Knowledge Base (KB) article 255676, DocumentComplete on IFRAME May Cause Cross-Domain Security Issues , http://support.microsoft.com/default.aspx?scid=kb;en-us;255676
Microsoft Knowledge Base (KB) article 258430, Web Site May Retrieve Cookies From Your Computer, http://support.microsoft.com/default.aspx?scid=kb;en-us;258430
Microsoft Knowledge Base (KB) article 261257, 'Malformed Component Attribute' Vulnerability in Internet Explorer, http://support.microsoft.com/default.aspx?scid=kb;en-us;261257
Microsoft Knowledge Base (KB) article 247333, Web Proxy Auto-Discovery "Spoofing" May Change Proxy Settings, http://support.microsoft.com/default.aspx?scid=kb;en-us;247333
Microsoft TechNet 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.

Acknowledgments

Microsoft thanks the following people for working with us to protect customers:

Mead & Company's Andrew Nosenko for reporting the "Frame Domain Verification" issue to us
Marc Slemko for reporting the "Unauthorized Cookie Access" vulnerability to us
UNYUN, the Shadow Penguin Security Research Group of Japan, for reporting the "Malformed Component Attribute" vulnerability to us.

Revisions

May 17, 2000: Bulletin Created.
August 09, 2000: Patch Availability section updated to advise of subsequently-released patch that eliminates other vulnerabilities in addition to those discussed here.

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