TUCoPS :: Browsers :: bt932.txt

Internet Explorer Object Data Remote Execution Vulnerability

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 (dcopley@eeye.com), 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 alert@eEye.com 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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