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Microsoft Security Bulletin (MS99-011)
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Patch Available for "DHTML Edit" Vulnerability
Originally Posted: April 21, 1999
Summary
=======
Microsoft has released a patch that eliminates a vulnerability in an ActiveX
control that is distributed in Internet Explorer 5 and downloadable for
Internet Explorer 4.0. The vulnerability could allow a malicious web site
operator to read information that a user had loaded into the control, and it
also could allow files with known names to be copied from the user's local
hard drive.
A fully supported patch is available to eliminate this vulnerability and
Microsoft recommends that affected customers download and install it, if
appropriate.
Issue
=====
The DHTML Edit control is an ActiveX control that is distributed with
Internet Explorer 5 and can be downloaded for use in Internet Explorer 4.0.
The control enables users to edit HTML text and see a faithful rendition of
how the text would look in the browser. There are two versions of the
control: a more powerful version that cannot be invoked by a web site
because it includes file access and other features, and a "safe for
scripting" version that has restricted functionality and is intended for use
by web sites.
The root cause of the vulnerability lies in the fact that a web site that
hosts the "safe for scripting" version of the control is able to upload any
data entered into the control. A malicious web site operator could trick a
user into entering sensitive data into a DHTML Edit control hosted on a web
page from the operator's site, and then upload the data. In addition, if the
malicious web site operator knows the name of a file on the user's local
drive, it is possible for the operator to programmatically load the file
into the control and then upload it.
The patch works by allowing a web site to load data from the control only if
it is in the site's domain. While there are no reports of customers being
adversely affected by this vulnerability, Microsoft is proactively releasing
this patch to allow customers to take appropriate action to protect
themselves against it.
Affected Software Versions
==========================
- Microsoft Internet Explorer 5 on Windows 95, Windows 98, and
Windows NT 4.0. Internet Explorer 5 on other platforms is
not affected.
- Microsoft Internet Explorer 4.0 on Windows 95, Windows 98 and
the x86 version of Windows NT 4.0. Internet Explorer 4.0 on
other platforms, including the Alpha version of Windows NT 4.0,
is not affected.
Note: The DHTML Edit control is included by default in Internet Explorer 5.
It is not included by default in Internet Explorer 4.0, but can be
downloaded and installed. Internet Explorer 4.0 customers who are unsure
whether they have installed the control should see What Customers Should Do.
What Microsoft is Doing
=======================
Microsoft has released patches that fix the problem identified. The patches
are available for download from the sites listed below in What Customers
Should Do.
Microsoft also has sent this security bulletin to customers
subscribing to the Microsoft Product Security Notification Service.
See http://www.microsoft.com/security/services/bulletin.asp for
more information about this free customer service.
Microsoft has published the following Knowledge Base (KB) article on this
issue:
- Microsoft Knowledge Base (KB) article Q226326,
Update Available for 'DHTML Edit' Security Issue,
http://support.microsoft.com/support/kb/articles/q226/3/26.asp.
(Note: It might take 24 hours from the original posting of this
bulletin for the KB article to be visible in the Web-based
Knowledge Base.)
What Customers Should Do
========================
Microsoft highly recommends that customers determine whether they are
potentially affected by the vulnerability:
- All copies of Internet Explorer 5 contain the DHTML Edit
control, so all Internet Explorer 5 customers are potentially
affected by the vulnerability.
- The only Internet Explorer 4.0 users who are potentially
affected by the vulnerability are those who have downloaded
and installed the DHTML Edit control. If this has been done,
the file dhtmled.ocx will be present on the hard drive. By
default, this file will be stored in the folder
C:\Program Files\Common Files\Microsoft Shared\Triedit\.
Customers who are potentially affected by the vulnerability should
evaluate the degree of risk that this vulnerability poses to their
systems and determine whether to download and install the patch.
The patch can be found at
http://www.microsoft.com/windows/ie/security/dhtml_edit.asp.
More Information
================
Please see the following references for more information related to this
issue.
- Microsoft Security Bulletin MS99-011,
Patch Available for DHTML Edit Vulnerability.
(The Web-posted version of this bulletin),
http://www.microsoft.com/security/bulletins/ms99-011.asp.
- Microsoft Knowledge Base (KB) article Q226326,
Update Available for 'DHTML Edit' Security Issue,
http://support.microsoft.com/support/kb/articles/q226/3/26.asp.
(Note: It might take 24 hours from the original posting of
this bulletin for the KB article to be visible in the Web-based
Knowledge Base.)
Obtaining Support on this Issue
===============================
If you require technical assistance with this issue, please
contact Microsoft Technical Support. For information on contacting
Microsoft Technical Support, please see
http://support.microsoft.com/support/contact/default.asp.
Acknowledgments
===============
Microsoft acknowledges Juan Carlos Cuartango of Spain for
discovering this vulnerability and reporting it to us.
Revisions
=========
- April 21, 1999: Bulletin Created.
For additional security-related information about Microsoft products, please
visit http://www.microsoft.com/security
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(c) 1999 Microsoft Corporation. All rights reserved.
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