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Title: Flaw in Windows Media Player Skins Downloading
could allow Code Execution (817787)
Date: 07 May 2003
Software: Microsoft Windows Media Player 7.1
Microsoft Windows Media Player for Windows XP
(Version 8.0)
Impact: Arbitrary code execution
Max Risk: Critical
Bulletin: MS03-017

Microsoft encourages customers to review the Security Bulletins at:
http://www.microsoft.com/technet/security/bulletin/MS03-017.asp
http://www.microsoft.com/security/security_bulletins/ms03-017.asp

---

Issue:

Microsoft Windows Media Player provides functionality to change the
overall appearance of the player itself through the use of "skins".
Skins are custom overlays that consist of collections of one or
more files of computer art, organized by an XML file. The XML file
tells Windows Media Player how to use these files to display a skin
as the user interface. In this manner, the user can choose from a
variety of standard skins, each one providing an additional visual
experience. Windows Media Player comes with several skins to choose
from, but it is relatively easy to create and distribute custom
skins.

A flaw exists in the way Windows Media Player 7.1 and Windows
Media Player for Windows XP handle the download of skin files.
The flaw means that an attacker could force a file masquerading
as a skin file into a known location on a user's machine.
This could allow an attacker to place a malicious executable
on the system.

In order to exploit this flaw, an attacker would have to host a
malicious web site that contained a web page designed to exploit
this particular vulnerability and then persuade a user to visit
that site - an attacker would have no way to force a user to the
site. An attacker could also embed the link in an HTML e-mail and
send it to the user.

In the case of an e-mail borne attack, if the user was using
Outlook Express 6.0 or Outlook 2002 in their default
configurations, or Outlook 98 or 2000 in conjunction with the
Outlook Email Security Update, then an attack could not be
automated and the user would still need to click on a URL sent
in the e-mail. However if the user was not using Outlook Express
6.0 or Outlook 2002 in their default configurations, or Outlook
98 or 2000 in conjunction with the Outlook Email Security Update,
the attacker could cause an attack that could both place, then
launch the malicious executable without the user having to click
on a URL contained in an e-mail.

The attacker's code would run with the same privileges as the
user: any restrictions on the user's ability to change the system
would apply to the attacker's code.

Mitigating Factors:

• Windows Media Player 9 Series is not affected by this issue.

• By default, Outlook Express 6.0 and Outlook 2002 open HTML
  mails in the Restricted Sites Zone. In addition, Outlook 98
  and 2000 open HTML mails in the Restricted Sites Zone if the
  Outlook Email Security Update, has been installed. Customers
  who use any of these products would be at no risk from an
  e-mail borne attack that attempted to automatically exploit
  these vulnerabilities.

• The attacker would have no way to force users to visit a
  malicious web site. Instead, the attacker would need to
  lure them there, typically by getting them to click on a
  link that would take them to the attacker's site.

Risk Rating:

• Critical

Patch Availability:

• A patch is available to fix this vulnerability. Please read the
  Security Bulletins at
  http://www.microsoft.com/technet/security/bulletin/ms03-017.asp
  http://www.microsoft.com/security/security_bulletins/ms03-017.asp

  for information on obtaining this patch.

Acknowledgment:

• Microsoft thanks Jouko Pynnonen of Oy Online Solutions Ltd,
  Finland and Jelmer for reporting this issue to us and working
  with us to protect customers.

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