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From:MICROSOFT <secure_(at)_microsoft.com>
Date:16.05.2002
Subject:Security Bulletin MS02-023: 15 May 2002 Cumulative Patch for Internet Explorer (Q321232)

- ----------------------------------------------------------------------
Title:      15 May 2002 Cumulative Patch for Internet Explorer
           (Q321232)
Date:       15 May 2002
Software:   Internet Explorer
Impact:     Six new vulnerabilities, the most serious of which could
           allow code of attacker's choice to run.
Max Risk:   Critical
Bulletin:   MS02-023

Microsoft encourages customers to review the Security Bulletin at:
http://www.microsoft.com/technet/security/bulletin/MS02-023.asp.
- ----------------------------------------------------------------------

Issue:
======
This is a cumulative patch that includes the functionality of all
previously released patches for IE 5.01, 5.5 and 6.0. In addition,
it eliminates the following six newly discovered vulnerabilities:


- A cross-site scripting vulnerability in a Local HTML Resource.
  IE ships with several files that contain HTML on the local file
  system to provide functionality. One of these files contains a
  cross-site scripting vulnerability that could allow a script to
  execute as if it were run by the user herself, causing it to run
  in the local computer zone. An attacker could craft a web page
  with a URL that exploits this vulnerability and then either host
  that page on a web server or send it as HTML email. When the web
  page was viewed and the user clicked on the URL link, the
  attacker's script injected into the local resource, the
  attacker's script would run in the Local Computer zone, allowing
  it to run with fewer restrictions than it would otherwise have.

- An information disclosure vulnerability related to the use of am
  HTML object provides that support for Cascading Style Sheets that
  could allow an attacker to read, but not add, delete or change,
  data on the local system. An attacker could craft a web page
  that exploits this vulnerability and then either host that page
  on a web server or send it as HTML email. When the page was
  viewed, the element would be invoked. Successfully exploiting this
  vulnerability, however, requires exact knowledge of the location
  of the intended file to be read on the user's system. Further,
  it requires that the intended file contain a single, particular
  ASCII character.

- An information disclosure vulnerability related to the handling
  of script within cookies that could allow one site to read the
  cookies of another. An attacker could build a special cookie
  containing script and then construct a web page with a hyperlink
  that would deliver that cookie to the user's system and invoke
  it. He could then send that web page as mail or post it on a
  server. When the user clicked the hyperlink and the page invoked
  the script in the cookie, it could potentially read or alter the
  cookies of another site. Successfully exploiting this, however,
  would require that the attacker know the exact name of the
  cookie as stored on the file system to be read successfully.

- A zone spoofing vulnerability that could allow a web page to be
  incorrectly reckoned to be in the Intranet zone or, in some very
  rare cases, in the Trusted Sites zone. An attacker could construct
  a web page that exploits this vulnerability and attempt to entice
  the user to visit the web page. If the attack were successful,
  the page would be run with fewer security restrictions than
  is appropriate.

- Two variants of the "Content Disposition" vulnerability
  discussed in Microsoft Security Bulletin MS01-058 affecting how
  IE handles downloads when a downloadable file's
  Content-Disposition and Content-Type headers are
  intentionally malformed. In such a case, it is possible for
  IE to believe that a file is a type safe for automatic
  handling, when in fact it is executable content. An attacker
  could seek to exploit this vulnerability by constructing a
  specially malformed web page and posting a malformed executable
  file. He could then post the web page or mail it to the intended
  target. These two new variants differ from the original
  vulnerability in that they for a system to be vulnerable, it
  must have present an application present that, when it is
  erroneously passed the malformed content, chooses to hand it
  back to the operating system rather than immediately raise
  an error. A successful attack, therefore, would require that
  the attacker know that the intended victim has one of these
  applications present on their system.

Finally, it introduces a behavior change to the Restricted Sites
zone. Specifically, it disables frames in the Restricted Sites
zone. Since the Outlook Express 6.0, Outlook 98 and Outlook 200
with the Outlook Email Security Update and Outlook 2002 all read
email in the Restricted Sites zone by default, this enhancement
means that those products now effectively disable frames in HTML
email by default. This new behavior makes it impossible for an
HTML email to automatically open a new window or to launch the
download of an executable.

Mitigating Factors:
====================
Cross-Site Scripting in Local HTML Resource:

- A successful attack requires that a user first click on a
  hyperlink. There is no way to automate an attack using
  this vulnerability.

- Outlook 98 and 2000 (after installing the Outlook Email
  Security Update), Outlook 2002, and Outlook Express 6 all
  open HTML mail in the Restricted Sites Zone. As a result,
  customers using these products would not be at risk from
  email-borne attacks.

- Customers using Outlook 2002 SP1 who have enabled the
  "Read as Plain Text" feature would be immune from the HTML
  email attack. This is because this feature disables all
  HTML elements, including scripting, from mail when it
  is displayed.

- Any limitations on the rights of the user's account
  would also limit the actions of the attacker's script.

- Customers who exercise caution in what web sites they
  visit or who place unknown or untrusted sites in the
  Restricted Sites zone can potentially protect themselves
  from attempts to exploit this issue on the web.

Local Information Disclosure through HTML Object:

- It can only be used to read information. It cannot add,
  change or delete any information.

- The attacker would need to know the exact name and
  location on the system of any file they attempted to read.

- Only files that contained a particular, individual ASCII
  character could be read. If this single character is not
  present, the attempt to read the file would fail.

- Outlook 98 and 2000 (after installing the Outlook Email
  Security Update), Outlook 2002, and Outlook Express 6 all
  open HTML mail in the Restricted Sites Zone. As a result,
  customers using these products would not be at risk from
  email-borne attacks.

- Customers using Outlook 2002 SP1 who have enabled the
  "Read as Plain Text" feature would be immune from the
  HTML email attack. This is because this feature disables
  all HTML elements, including scripting, from mail when it
  is displayed.

Script within Cookies Reading Cookies:

- The specific information an attacker could access would
  depend on what information a site has chosen to store in
  its cookies. Best practices strongly recommend against
  storing sensitive information in cookies.

- An attacker would have to entice a user to first click on
  a hyperlink to initiate an attempt to exploit this
  vulnerability. There is no way to automate an attack that
  exploits this vulnerability.

- Mounting a successful attack requires that the attacker
  know the exact name of the target cookie. This
  vulnerability provides no means for an attacker to
  acquire that information.

- Outlook 98 and 2000 (after installing the Outlook Email
  Security Update), Outlook 2002, and Outlook Express 6
  all open HTML mail in the Restricted Sites Zone. As a
  result, customers using these products would not be at
  risk from email-borne attacks.

- Customers using Outlook 2002 SP1 who have enabled the
  "Read as Plain Text" feature would be immune from the
  HTML email attack. This is because this feature disables
  all HTML elements, including scripting, from mail when it
  is displayed.

Zone Spoofing through Malformed Web Page:

- A successful attack would require NetBIOS connectivity
  between the user and the attacker's site. Any filtering
  of NetBIOS, such as that found by ISP's or at the firewall
  perimeter, would thwart attempts to exploit this
  vulnerability.

- Any attempt to render a web site in the Trusted Sites zone
  would require very specific knowledge of custom configuration
  made by the user. This aspect of the vulnerability is not
  exploitable by default, nor does the vulnerability give the
  means to acquire the necessary information for that attack.

New Variants of the "Content Disposition" Vulnerability:

- Any successful attempt to exploit this vulnerability requires
  that the attacker know that the intended target have specific
  versions of specific applications on their system. The
  vulnerability gives no means for an attacker to know what
  applications or versions are present on the system.

- Any attempt to exploit the vulnerability requires that the
  attacker host a malicious executable on a server accessible
  to the intended victim. If the hosting server is
  unreachable for any reason, such as DNS blocking or the
  server being taken down, the attack would fail.

Risk Rating:
============
- Internet systems: Critical
- Intranet systems: Critical
- Client systems: Critical

Patch Availability:
===================
- A patch is available to fix this vulnerability. Please read the
  Security Bulletin at
  http://www.microsoft.com/technet/security/bulletin/ms02-023.asp
  for information on obtaining this patch.

Acknowledgment:
===============
- Jani Laatikainen ([email protected]) for reporting one of the
  "Content-Disposition variants.
- Yuu Arai of LAC SNS Team (http://www.lac.co.jp/security/) for
  reporting one of the "Content-Disposition variants.
- Cistobal Bielza Lino and Juan Carlos G. Cuartango from
  Instituto Seguridad Internet (www.instisec.com) for reporting
  the Zone Spoofing through Malformed Web Page vulnerability.

- ---------------------------------------------------------------------

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