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Microsoft Security Bulletin MS99-011 - Critical

Patch Available for "DHTML Edit" Vulnerability

Published: April 21, 1999 | Updated: July 29, 2003

Version: 2.0

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.

Vulnerability Identifier: CVE-1999-0487

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 The Microsoft Product Security Notification Service for more information about this free customer service.

Microsoft has published the following Knowledge Base (KB) article on this issue:

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.

More Information

Please see the following references for more information related to this issue.

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/contactussupport/?ws=support.

Acknowledgements

Microsoft acknowledges Juan Carlos Cuartango of Spain for discovering this vulnerability and reporting it to us.

Revisions

  • April 21, 1999: Bulletin Created.
  • V2.0 (July 29, 2003): Introduced versioning and updated patch availability information.

For additional security-related information about Microsoft products, please visit http://www.microsoft.com/technet/security

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