Microsoft Security Bulletin (MS00-039)
Patch Available for "SSL Certificate Validation" Vulnerabilities
Originally posted: June 05, 2000
Microsoft has released a patch that eliminates two security
vulnerabilities in Microsoft(r) Internet Explorer. The
vulnerabilities involve how IE handles digital certificates; under a
very daunting set of circumstances, they could allow a malicious web
site operator to pose as a trusted web site.
In addition to eliminating the "SSL Certificate Validation"
vulnerabilities, this patch also eliminates all vulnerabilities
discussed in Microsoft Security Bulletin MS00-033.
Frequently asked questions regarding this vulnerability and the
patch can be found at
Two vulnerabilities have been identified in the way IE handles digital
- When a connection to a secure server is made via either an
image or a frame, IE only verifies that the server's SSL
certificate was issued by a trusted root - it does not verify the
server name or the expiration date. When a connection is made via
any other means, all expected validation is performed.
- Even if the initial validation is made correctly, IE does not
re-validate the certificate if a new SSL session is established
with the same server during the same IE session.
The circumstances under which these vulnerabilities could be exploited
are fairly restricted. In both cases, it is likely that the attacker
would need to either carry out DNS cache poisoning or physically
replace the server in order to successfully carry out an attack via
this vulnerability. The timing would be especially crucial in the
second case, as the malicious user would need to poison the cache or
replace the machine during the interregnum between the two SSL
Affected Software Versions
- Microsoft Internet Explorer 4.0
- Microsoft Internet Explorer 4.01
- Microsoft Internet Explorer 5.0
- Microsoft Internet Explorer 5.01
Note: This patch also eliminates all vulnerabilities discussed in
Microsoft Security Bulletin MS00-033.
Note: The patch requires IE 5.01 to install; a version that supports
IE 4.01 Service Pack 2 will be released shortly. Customers who
install this patch on versions other than 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
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 MS00-039,
- Microsoft Knowledge Base article Q254902 discusses this issue and
will be available soon.
- Microsoft TechNet Security web site,
Obtaining Support on this Issue
This is a fully supported patch. Information on contacting Microsoft
Support is available at
Microsoft thanks the ACROS Penetration Team, Slovenia, for reporting
this issue to us and working with us to protect customers.
- June 05, 2000: Bulletin Created.
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Last Updated June 05,2000