FedCIRC Advisory FA-98-93

Original issue date: October 19, 1998
Source: Microsoft

Topic: Untrusted Scripted Paste in Microsoft Internet Explorer 4.01

To aid in the wide distribution of essential security information, FedCIRC is forwarding the following information from Microsoft. Microsoft urges you to act on this information as soon as possible. Microsoft contact information is included in the forwarded text below; please contact them if you have any questions or need further information.

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Microsoft Security Bulletin (MS98-015)
------------------------------------------------------------
Update available for "Untrusted Scripted Paste" Issue in
Microsoft Internet Explorer 4.01

Originally Posted: October 16, 1998
Last Revised: October 16, 1998

Summary
=======
Microsoft has released a patch that fixes a vulnerability involving scripted
pastes that has been discovered with Internet Explorer 4.01 on Win32 and
Win16 platforms. The vulnerability could make it possible for a malicious
hacker to create a web site that, when visited, is able to use script to
read a file on the user's system. The file must be in a location known to
the malicious hacker. This has also been referred to as the "Cuartango"
vulnerability.

Microsoft highly recommends that users that have affected software installed
on their systems should download and install the available patch as soon as
possible.

Issue
=====
The "Untrusted Scripted Paste" issue involves a vulnerability in Internet
Explorer that could allow a malicious hacker to circumvent certain Internet
Explorer security safeguards. This vulnerability makes it possible for a
malicious Web site operator to read the contents of a file on the user's
computer if the hacker 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
to which the user has access, and whose direct path name is known by the
attacker.

The nature of this problem is that a script is able to use the
Document.ExecCommand function to paste a filename into the file upload
intrinsic control, which should only be possible by explicit user action. As
a result, a subsequent form submission could send the file to a remote web
site unbeknownst to the user if the user has disabled the default warning
that is displayed when submitting unencrypted forms (see "Administrative
Workaround" below for information on re-enabling this functionality).

While there have not been any reports of customers being adversely affected
by these problems, Microsoft is releasing a patch to address any risks posed
by this issue.

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

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 October 16th Microsoft released a patch that fixes the problem
identified. This patch is available for download from the sites listed
below.

Microsoft has sent this security bulletin to customers subscribing to the
Microsoft Product Security Notification Service (see
http://www.microsoft.com/security/bulletin.htm for more information about
this free customer service).

Microsoft has published the following Knowledge Base (KB) articles on this
issue:
 - Microsoft Knowledge Base (KB) article Q169245,
   Update available for "Untrusted Scripted Paste" Issue
   http://support.microsoft.com/support/kb/articles/q169/2/45.asp

What customers should do
========================
Microsoft highly recommends that users that have affected software installed
on their systems should download and install the available patch as soon as
possible. Complete URLs for each affected software version is given below.

Windows 98
----------
Windows 98 customers can obtain the 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/ie/security/paste.htm

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. This warning prompt makes sure users are aware 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" form 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" (or "Disable" if you prefer).

These same procedures 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. Customers can use the Zones security feature in Internet
Explorer 4 to disable Active Scripting (VBScript and JScript) in untrusted
or unknown Internet sites, while still permitting known and trusted sites
that use JScript and VBScript to work properly.

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.
5. These same procedures 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.

 - Microsoft Security Bulletin MS98-015,
   Update available for "Untrusted Scripted Paste" Issue
   in Microsoft Internet Explorer 4.01, (the Web posted
   version of this bulletin),
   http://www.microsoft.com/security/bulletins/ms98-015.htm
 - Microsoft Knowledge Base (KB) article Q169245,
   Update available for "Untrusted Scripted Paste" Issue
   http://support.microsoft.com/support/kb/articles/q169/2/45.asp

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/support/contact/default.asp

Acknowledgements
================
This bug was first reported by Juan Carlos Garcia Cuartango from Spain.

Revisions
=========
 - October 16, 1998: Bulletin Created

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

------------------------------------------------------------

THE INFORMATION PROVIDED IN THE MICROSOFT KNOWLEDGE BASE IS PROVIDED "AS IS"
WITHOUT WARRANTY OF ANY KIND. MICROSOFT DISCLAIMS ALL WARRANTIES, EITHER
EXPRESS OR IMPLIED, INCLUDING THE WARRANTIES OF MERCHANTABILITY AND FITNESS
FOR A PARTICULAR PURPOSE. IN NO EVENT SHALL MICROSOFT CORPORATION OR ITS
SUPPLIERS BE LIABLE FOR ANY DAMAGES WHATSOEVER INCLUDING DIRECT, INDIRECT,
INCIDENTAL, CONSEQUENTIAL, LOSS OF BUSINESS PROFITS OR SPECIAL DAMAGES, EVEN
IF MICROSOFT CORPORATION OR ITS SUPPLIERS HAVE BEEN ADVISED OF THE
POSSIBILITY OF SUCH DAMAGES. SOME STATES DO NOT ALLOW THE EXCLUSION OR
LIMITATION OF LIABILITY FOR CONSEQUENTIAL OR INCIDENTAL DAMAGES SO THE
FOREGOING LIMITATION MAY NOT APPLY.


(c) 1998 Microsoft and/or its suppliers. All rights reserved.
For Terms of Use see http://support.microsoft.com/support/misc/cpyright.asp.



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