Title: Flaws in Web Server Certificate Validation Could
Enable Spoofing
Date: 16 May 2001
Software: Internet Explorer
Impact: Spoofing of trusted web site
Bulletin: MS01-027
Microsoft encourages customers to review the Security Bulletin at:
http://www.microsoft.com/technet/security/bulletin/MS01-027.asp.
A patch is available to eliminate two newly discovered
vulnerabilities
affecting Internet Explorer, both of which could enable an attacker
to
spoof trusted web sites. The first vulnerability involves how digital
certificates from web servers are validated. When CRL checking for
such
certificates is enabled, it could be possible for any or all of the
following checks to no longer be performed:
The second vulnerability could enable a web page to display the URL
from a different web site in the IE address bar. This spoofing could
occur within a valid SSL session with the impersonated site. Both
vulnerabilities could be used to convince a user that the attacker's
web site was actually a different one - one that the user presumably
trusts and would provide sensitive information to. However, as
discussed in the Mitigating Factors section below, there would be
significant hurdles to exploiting either vulnerability.
In addition to eliminating the two new vulnerabilities, the patch
also
eliminates two new variants of a previously discussed vulnerability,
the "Frame Domain Verification" vulnerability, which originally was
discussed in Microsoft Security Bulletin MS00-033. Like the original
version, these new variants vulnerability could enable a malicious
web
site operator to open two browser windows, one in the web site's
domain
and the other on the user's local file system, and to pass
information
from the latter to the former. This could enable the web site
operator
to read any file on the user's local computer that could be opened in
a
browser window.
The patch also incorporates the functionality of the patch provided
in
Microsoft Security Bulletin MS01-020
(http://www.microsoft.com/technet/security/bulletin/MS01-020.asp).
Server certificate validation vulnerability:
Web page spoofing vulnerability:
New variants of "Frame Domain Verification" vulnerability:
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