EEYE: Internet Explorer Object Data Remote Execution Vulnerability

From: Marc Maiffret (marc_at_EEYE.COM)
Date: 08/21/03

  • Next message: Russ: "SP4 reverts MS03-026 - Not!"
    Date:         Thu, 21 Aug 2003 11:56:36 -0700

    The first time I sent this email it included example HTML code. That HTML
    code would have no affect on eMail clients as this is not a HTML email nor
    was the data properly formatted, etc..., etc... However, due to VERY POORLY
    written mail gateways, this eMail was being blocked at most gateways as
    being a virus etc... Hence I have removed that data (you can find it on the
    eEye website) and I am resending the advisory. So no need to eMail me about
    this, I am aware of all those using poorly written software to protect their
    organization, McAfee Groupshield being the biggest culprit.


    Internet Explorer Object Data Remote Execution Vulnerability

    Release Date:
    August 20, 2003

    Reported Date:
    May 15, 2003

    High (Remote Code Execution)

    Systems Affected:
    Microsoft Internet Explorer 5.01
    Microsoft Internet Explorer 5.5
    Microsoft Internet Explorer 6.0
    Microsoft Internet Explorer 6.0 for Windows Server 2003

    eEye Digital Security has discovered a security vulnerability in Microsoft's
    Internet Explorer that would allow executable code to run automatically upon
    rendering malicious HTML.

    This is a flaw in Microsoft's primary contribution to HTML, the Object tag,
    which is used to embed basically all ActiveX into HTML pages. The parameter
    that specifies the remote location of data for objects is not checked to
    validate the nature of the file being loaded, and therefore trojan
    executables may be run from within a webpage as silently and as easily as
    Internet Explorer parses image files or any other "safe" HTML content.

    This attack may be utilized wherever IE parses HTML, including web sites,
    e-mail, newsgroups, and within applications utilizing web-browsing


    On Windows 2003 Internet Explorer, this upgrade is noted as being "moderate"
    rather than "critical." This is said to be because of Windows 2003's
    "Enhanced Security Configuration Mode." In plain English, this just means
    that Microsoft checked the "Disable ActiveX" box on Internet Explorer's
    Security Properties. Windows 2003 Internet Explorer also disables by default
    Visual Basic Script, Javascript, input forms, and even the ability to
    download files.

    Due to the popularity and prevalence of ActiveX on the Internet, users
    running Windows 2003 "Enhanced Security Configuration" Mode may have chosen
    to reactivate the ability to view active content. These users should be
    aware that they are at critical risk for this vulnerability and should apply
    the necessary patch.

    Lastly, Microsoft attributes credit to eEye for this bug, stating it is the
    "Object Type" bug. They do this after noting a variant of the "Object Type"
    bug was found to be still vulnerable on certain language based systems.
    However, the "Object Type" bug was our previous "Object" tag vulnerability.
    That issue involved a stack based overflow in the "Type" property. This
    current issue involves incorrect handling of the data specified by the
    "Data" tag.

    Technical Description:

    [Data Removed] We have removed the example data from this eMail due to mail
    gateway filters not functioning properly and believing this eMail is a
    virus. For the full advisory with all technical details please visit:

    This example is in the more traditional vein. In house, we set up a
    demonstration system that silently loaded "bo2k" and "subseven" trojans from
    within a single webpage.

    The above example shows an entirely legitimate session. The only trick to
    this is that the "Data" URL must not end in an unsafe extension (e.g.,
    ".exe", ".bat", etc). The "Content-Type" tag returned by the server is
    treated by Internet Explorer as authoritative.

    In other words, the client asks for a safe file, the server returns an
    unsafe file, and Internet Explorer does not know what hit it.

    What Internet Explorer should be doing in this case is not loading the
    unsafe document at all, or it should prompt the user with a severe warning
    about this file, with the default option being to save the file to disk.

    We can generally guess what is going on here. As .hta or "HTML Application"
    files are not binary and resemble - mechanically - HTML files, IE's check of
    content will be unable to return that this file is anything but safe. The
    second check of MIME type will see that we are requesting a safe file
    type... and the third check of MIME type will be from the server saying this
    is a HTML Application. For whatever reason, IE has ignored the returned MIME
    type from a security context, but paid attention to it from an execution

    This attack was discovered through manual testing techniques. The hypothesis
    was: "Internet Explorer has many avenues where it might be presented with
    executable content. One of these avenues must be broken so that executable
    content might be automatically run."

    Retina Network Security Scanner has been updated to identify this latest
    Internet Explorer vulnerability.

    Vendor Status:
    Microsoft was notified and has released a patch for this vulnerability. The
    patch is available at:

    Drew Copley (, Research Engineer, eEye Digital Security

    Greetings: Liu Die Yu, http-equiv, Stone Fisk, Dror Shalev, the Shrug,
    Oliver Lavery, Brett Moore, Chung's Donut Shop, Jolly

    Copyright (c) 1998-2003 eEye Digital Security
    Permission is hereby granted for the redistribution of this alert
    electronically. It is not to be edited in any way without express consent of
    eEye. If you wish to reprint the whole or any part of this alert in any
    other medium excluding electronic medium, please e-mail for

    The information within this paper may change without notice. Use of this
    information constitutes acceptance for use in an AS IS condition. There are
    NO warranties with regard to this information. In no event shall the author
    be liable for any damages whatsoever arising out of or in connection with
    the use or spread of this information. Any use of this information is at the
    user's own risk.

    Please send suggestions, updates, and comments to:

    eEye Digital Security

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