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securityvulnsSecurityvulnsSECURITYVULNS:DOC:1641
HistoryMay 24, 2001 - 12:00 a.m.

Security Bulletin MS01-029

2001-05-2400:00:00
vulners.com
30

Title: Windows Media Player .ASX Processor Contains Unchecked
Buffer
Date: 23 May 2001
Software: Windows Media Player 6.4 and 7
Impact: Potentially run code of attacker's choice.
Bulletin: MS01-029

Microsoft encourages customers to review the Security Bulletin at:
http://www.microsoft.com/technet/security/bulletin/MS01-029.asp.


Issue:

This bulletin discusses two security vulnerabilities that are related
to each other only by the fact that they affect Windows Media Player.
We packaged them in a single patch for customers using Windows Media
Player 6.4 to make it more convenient for customers to apply. For
customers using Windows Media Player 7, both security vulnerabilities
are addressed by upgrading to Windows Media Player 7.1.

The two vulnerabilities are:

  • A buffer overrun in the functionality used to process Active
    Stream
    Redirector (.ASX) files. This vulnerability is a variant of the
    buffer
    overrun vulnerability identified in Microsoft Security Bulletin
    (MS00-090). Windows Media Player supports the use of .ASX files to
    enable users to play streaming media that resides on intranet or
    Internet sites and allows the use of playlists. However, the code
    that parses .ASX files has an unchecked buffer, and this could
    potentially enable a malicious user to run code of her choice on the
    machine of another user. The attacker could either send an affected
    file to another user and entice him to run or preview it, or she
    could
    host such a file on a web site and cause it to launch automatically
    whenever a user visited the site. The code could take any action on
    the machine that the legitimate user himself could take.

  • A vulnerability affecting how Windows Media Player handles
    Internet
    shortcuts. Windows Media Player has a flaw that causes it to save
    Internet shortcuts to the user's Temporary Files folder with a fixed
    known filename. This results in a security vulnerability because it's
    possible for HTML code to be stored in such a shortcut and launched
    via
    a web page or HTML e-mail, in which case the code would run in the
    Local Computer Zone rather than the Internet Zone. An attacker could
    exploit this vulnerability to read - but not add, delete or modify -
    files on another user's computer.

  • In addition, this patch provides a solution to a potential privacy
    vulnerability that was recently identified. This issue could be
    exploited by a malicious set of web sites to distinguish a user.
    While
    this issue would not by itself enable a web site to identify the
    user,
    it could enable the correlation of user information to potentially
    build a composite description of the user. .Users can protect
    themselves by installing the above patch or upgrading to Windows
    Media
    Player 7.1, then changing the appropriate settings in their player as
    outlined below to prevent sets of websites from potentially profiling
    using Windows Media Player.

  • In Windows Media Player 6.4, the privacy setting is selected via a
    new option, which can be reached by going to the menu item View /
    Options then selecting the player tab and de-selecting "Allow
    Internet
    sites to uniquely identify your player".

  • In Windows Media Player 7.1, the privacy setting is toggled via
    the
    existing option under the tools menu, on the player tab and deselect
    the option "Allow Internet sites to uniquely identify your player".

Although we typically do not discuss privacy issues in security
bulletins, the privacy issue in this case is eliminated by applying
the
patch and then selecting the new user settings as described above. We
have provided this information because the best way to make the
privacy
update available to customers was by including it in this patch, and
because we wanted to provide users who installed the patch with
information about how to use the new privacy settings.

Mitigating Factors:

Buffer overrun vulnerability:

  • The attacker would need the ability to entice the user into either
    visiting a web site she controlled, or opening an HTML e-mail she had
    prepared.

  • The attacker would need to know the specific operating system that
    the user was running in order to tailor the attack code properly; if
    the attacker made an incorrect guess about the user's operating
    system
    platform, the attack would crash the user's application, but not run
    code of the attacker's choice.

Internet shortcut vulnerability:

  • On Windows NT 4.0 and Windows 2000 systems, the location of the
    Temporary Files folder varies from user to user. In order to exploit
    the vulnerability on these systems, the attacker would need to know
    the
    exact location of the Temporary Files folder on the specific system
    she
    wished to attack.

  • The attacker would need to know the exact name of each file she
    wished to read.

  • The attacker could only view file types that can be opened in a
    browser window. These include.txt, .jpg, .gif, or .htm , but not file
    types such as .exe, .doc, and .xls.

  • There is no capability to add, delete or changes files via this
    vulnerability.

Patch Availability:


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