Microsoft Security Bulletin MS01-055 (Version 2.0)

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Title:      13 November 2001 Cumulative Patch for IE
Released:   08 November 2001
Revised:    13 November 2001 (version 2.0)
Software:   Internet Explorer
Impact:     Exposure and altering of data in cookies
Max Risk:   Moderate
Bulletin:   MS01-055

Microsoft encourages customers to review the Security Bulletin at:
http://www.microsoft.com/technet/security/bulletin/MS01-055.asp.
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Reason for Revision:
====================
On November 08, 2001, Microsoft released the original version of
this bulletin. In it, we detailed a work-around procedure that
customers could implement to protect themselves against a publicly
disclosed vulnerability. On November 13, 2001, we released a patch
that, when applied, eliminates all known vulnerabilities affecting
IE 5.5 and IE 6. We therefore expanded the scope of the bulletin to
discuss all of the vulnerabilities the patch addresses. Customers
who disabled Active Scripting per the original version of this
bulletin can re-enable it after installing this patch.

Issue:
======
In addition to eliminating all previously discussed vulnerabilities 
affecting IE 5.5 Service Pack 2 and IE 6, the patch also eliminates
three newly discovered ones: 

The first two involve how IE handles cookies across domains.
Although the underlying flaws are completely unrelated, the scope
is exactly the same - in each case, a malicious user could
potentially craft a URL that would allow them to gain unauthorized
access to a user's cookies and potentially modify the values
contained in them. Because some web sites store sensitive
information in a user's cookies, this could allow personal
information to be compromised. Both vulnerabilities could be
exploited either by hosting specially crafted URL's on a web page
or by sending them to the victim in an HTML email.

The third vulnerability is a new variant of a vulnerability
discussed in Microsoft Security Bulletin MS01-051 affecting how
IE handles URLs that include dotless IP addresses. If a web site
were specified using a dotless IP format (e.g.,
http://031713501415 rather than http://207.46.131.13), and the
request were malformed in a particular way, IE would not recognize
that the site was an Internet site. Instead, it would treat the
site as an intranet site, and open pages on the site in the
Intranet Zone rather than the correct zone. This would allow the
site to run with fewer security restrictions than appropriate.
This vulnerability does not affect IE 6.

Mitigating Factors:
====================
Cookie Handling Vulnerabilities: 

 - To exploit either vulnerability, the attacker would need to
   entice the user into visiting a particular web site or opening
   an HTML e-mail containing the malformed URL.

 - The Outlook Email Security Update (which is included as part
   of Outlook 2002 in Office XP) would protect the user against the
   mail-borne attack scenario. 

 - Users who have set Outlook Express to use the "Restricted Sites"
   Zone are not affected by the mail-borne attack scenario, because
   the "Restricted Sites" zone sets Active Scripting to disabled.
   Note that this is the default setting for Outlook Express 6.0.
   Users of Outlook Express 6.0 should verify that Active Scripting
   is still disabled in the Restricted Sites Zone.
 
Zone Spoofing Vulnerability: 
 - The default settings in the Intranet Zone differ in only a few
   ways from those of the Internet Zone. The differences are
   enumerated in the FAQ in MS01-051, but none would allow
   destructive action to be taken.

Patch Availability:
===================
 - A patch is available to fix this vulnerability. Please read the 
   Security Bulletin at
   http://www.microsoft.com/technet/security/bulletin/ms01-055.asp
   for information on obtaining this patch.

Acknowledgment:
===============
 - Marc Slemko for reporting one of the cookie handling issues.

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