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Microsoft Security Bulletin MS98-015 - Critical

Update available for "Untrusted Scripted Paste" Issue in Microsoft Internet Explorer 4.01

Published: October 16, 1998 | Updated: May 16, 2003

Version: 2.0

Originally Posted: October 16, 1998
Updated: May 16, 2003

Summary

On November 18th Microsoft released an updated version of the patch for the "Untrusted Scripted Paste" vulnerability. This vulnerability, also known as the "Cuartango" vulnerability, could enable a malicious web site operator to use scripted paste operations to read a file that resides in a known location on a user's system. The updated patch fixes the original vulnerability as well as a newly-discovered variant.

Microsoft highly recommends that all affected customers -- including anyone who downloaded the original patch before November 18 -- download and install the updated patch to protect their computers.

Issue

The "Untrusted Scripted Paste" issue involves a vulnerability in Internet Explorer® that could allow a malicious web site operator to circumvent certain Internet Explorer security safeguards. This vulnerability makes it possible for the operator to read the contents of a file on the user's computer if he knows the exact name and path of the targeted file. This could also be used to view the contents of a file on the user's network, if the user has access to it and the malicious operator knows its direct path name.

The underlying problem is the ability of a script to use the Document.ExecCommand function to paste a filename into the file upload intrinsic control. This should only be possible by explicit user action. Once the filename has been pasted into the control, a subsequent form submission could send the file to a remote web site. If the user has disabled the default warning that is displayed when submitting unencrypted forms, the file would be sent without any warning to the user. (See "Administrative Workaround" below for information on re-enabling this functionality).

Although the original patch corrected the problem, another method of putting a filename into the file upload intrinsic control was discovered subsequently. The updated patch addresses both the original problem and the newly-discovered variant.

Affected Software Versions

  • Microsoft® Internet Explorer 4.01 and 4.01 SP1 on Windows NT® 4.0, Windows 95
  • Microsoft Windows® 98, with integrated Internet Explorer
  • Microsoft Internet Explorer 4.01 for Windows 3.1 and Windows NT 3.51

Vulnerability Identifier: CVE-1999-0870

This vulnerability could also affect software that uses HTML functionality provided by Internet Explorer, even if Internet Explorer is not used as your default browser. All customers that have affected versions of Internet Explorer on their systems should install this patch, whether or not they use Internet Explorer for web browsing.

This vulnerability does not affect Internet Explorer 3.x or 4.0 on any platform.
This does not affect any Macintosh or UNIX versions of Internet Explorer.

What Microsoft is Doing

On November 18th, Microsoft released an updated version of this patch. The updated version fixes the original problem, as well as a subsequently identified variant. This patch is available for downloading from the sites listed below.

Microsoft 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) articles on this issue:

What customers should do

Microsoft highly recommends that all affected customers -- including anyone who downloaded the original patch before November 18 -- download the updated patch to protect their computers. The complete URL for each affected software version is given below.

Windows 98
Windows 98 customers can obtain the updated patch using Windows Update. To obtain this patch using Windows Update, launch Windows Update from the Windows Start Menu and click "Product Updates." When prompted, select 'Yes' to allow Windows Update to determine whether this patch and other updates are needed by your computer. If your computer does need this patch, you will find it listed under the "Critical Updates" section of the page.

Internet Explorer 4.01
Customers using Internet Explorer 4.01 can obtain the patch from the Internet Explorer Security web site, http://www.microsoft.com/technet/security/patchavailability.mspx

Administrative Workaround

Microsoft strongly encourages customers to apply the patch. However, there are additional actions that can be taken to ensure safe computing:

If the user has disabled the default warning that is displayed when submitting unencrypted forms, re-enabling this feature can provide additional protection. The warning prompt makes sure users are alerted if a script attempts to submit data using forms. Users should be cautious if they see this warning when browsing and have not actually chosen to submit any data.

To turn on this prompt:

  1. From Internet Explorer, choose "Internet Options" from the "View" menu.
  2. Click on the tab labeled "Security".
  3. Click on "Internet Zone", then click "Customize Settings".
  4. Scroll to "Submit non-encrypted form data" and click on "Prompt".

The same procedure should be followed for the "Restricted Sites" Zone.

Additionally, users who cannot apply the patch immediately can disable Active Scripting technologies in Internet Explorer to protect themselves from this issue. Please note that the Zones security feature in Internet Explorer 4 can be used to disable Active Scripting (VBScript and JScript) in untrusted or unknown Internet sites, while still permitting it in trusted and known sites.

To turn off Active Scripting for the "Internet" Zone:

  1. From Internet Explorer, choose "Internet Options" from the "View" menu.
  2. Click on the tab labeled "Security".
  3. Click on "Internet Zone", then click "Customize Settings".
  4. Scroll to the bottom of the list and click on "Disable" under the "Active Scripting" setting.

The same procedure should be followed for the "Restricted Sites" Zone.

Sites that are trusted to use JScript and VBScript can be added to the Trusted Zones list. For more information on using Zones, please see the Online Help included with Internet Explorer.

More Information

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

Obtaining Support on this Issue

This is a supported patch for Internet Explorer. If you have problems installing this patch or require technical assistance with this patch, please contact Microsoft Technical Support. For information on contacting Microsoft Technical Support, please see http://support.microsoft.com/contactussupport/?ws=support

Acknowledgments

This bug was originally reported to Microsoft by Juan Carlos Garcia Cuartango of Spain. Mr. Cuartango also reported the new variant of this issue. We are grateful for his assistance.

Revisions

  • October 16, 1998: Bulletin Created
  • November 18, 1998: Updated bulletin to include information on updated patch that fixes variation of original issue.
  • V2.0 (May 16, 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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