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Home » Hacking News » Windows Media Player .ASX Processor Contains Unchecked Buffer

Windows Media Player .ASX Processor Contains Unchecked Buffer

by phiber on May 24th, 2001 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.

    Vulnerability identifier:

    Buffer overrun vulnerability: CAN-2001-0242

    Internet shortcut vulnerability: CAN-2001-0243

    Patch availability

    Download locations for this patch

    Windows Media Player 6.4:

    Windows Media Player 7:

    Upgrade to Windows Media Player 7.1

    Microsoft Security Bulletin MS 01-29.

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