Microsoft Security Bulletin (MS00-033)
Patch Available for "Frame Domain Verification", "Unauthorized Cookie
Access", and "Malformed Component Attribute" Vulnerabilities
Originally Posted: May 17, 2000
Microsoft has released a comprehensive patch that eliminates three
security vulnerabilities in Microsoft(r) 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.
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 them 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
placed 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
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: The patches require IE 4.01 Service Pack 2 or IE 5.01 to
install. Customers using versions prior to these may receive a
message reading "This update does not need to be installed on this
system". This message is incorrect. More information is available in
KB article Q262509.
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 MS00-033,
- Microsoft Knowledge Base article Q262509 discusses the overall
patch and will be available soon.
- Microsoft Knowledge Base articles Q251108 and 255676 discuss
the "Frame Domain Verification" vulnerability and will be
- Microsoft Knowledge Base article Q258430 discusses the
"Unauthorized Cookie Access" vulnerability and will be available
- Microsoft Knowledge Base article Q261257 discusses the
"Malformed Component Attribute" vulnerability and will be
- Microsoft Knowledge Base (KB) article Q247333,
Web Proxy Auto-Discovery "Spoofing" May Change Proxy Settings,
- Microsoft TechNet Security web site,
Obtaining Support on this Issue
This is a fully supported patch. Information on contacting Microsoft
Technical Support is available at
Microsoft thanks the following people for working with us to protect
- 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
- May 17, 2000: Bulletin Created.
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Last updated May 17, 2000