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Category:   Application (Web Browser)  >   Microsoft Internet Explorer Vendors:   Microsoft
Microsoft Internet Explorer Drag-and-Drop Timing May Let Remote Users Install Arbitrary Files
SecurityTracker Alert ID:  1015049
SecurityTracker URL:  http://securitytracker.com/id/1015049
CVE Reference:   CVE-2005-3240   (Links to External Site)
Date:  Feb 14 2006
Impact:   Modification of system information, Modification of user information, User access via network
Vendor Confirmed:  Yes  
Version(s): 5.01, 5.5, 6.0
Description:   Matthew Murphy reported a vulnerability in Microsoft Internet Explorer. A remote user can cause arbitrary code to be executed on the target user's system. Some interaction with the target user is required to exploit this vulnerability.

The Internet Explorer (IE) browser does not properly process certain drag-and-drop events. A remote user can create HTML that exploits the timing of a target user's drag-and-drop operation to potentially cause arbitrary files to be installed on the target user's system.

IE permits file objects within a folder view to be dragged. A remote user can create specially crafted HTML. When the target user drags an object within the top-level window of the specially crafted HTML, then the remote user's scripting code can potentially redirect the target user's inputs to other top-level windows. The exploitability depends on the ability of the HTML code to predict the timing of the drag event.

The vendor was notified on August 3, 2005.

Impact:   A remote user may be able to cause an arbitrary file to be written to a specified location on the target user's system. Some interaction with the target user is required.
Solution:   No solution was available at the time of this entry. The vendor plans to include a fix as part of Windows Server 2003 SP2 and Windows XP SP3. No fix is planned for Windows 2000.

The vendor has posted limited information on the vulnerability at:

http://blogs.technet.com/msrc/archive/2006/02/13/419439.aspx

The author of the report has provided the following unofficial workarounds [quoted]:

1. Set a Kill Bit on the Shell.Explorer Control
-----------------------------------------------

Setting a kill bit on this control will prevent Internet Explorer from displaying the
rich folder view interface that gives rise to this attack. For more information
about setting kill bits, please see Microsoft Knowledge Base Article 240797:

http://support.microsoft.com/kb/240797

The CLSID of this component as deployed on Windows XP is:

{8856F961-340A-11D0-A96B-00C04FD705A2}

Tools to automate the process of setting this kill bit have been provided at:

http://student.missouristate.edu/m/matthew007/tools/shellkill.zip
PGP signature: http://student.missouristate.edu/m/matthew007/tools/shellkill.zip.asc

Included in this archive are an Administrative Template (.adm) and a VBScript file
(.vbs) which implement this setting. The Administrative Template also allows an
administrator to work around a specific case of functionality loss caused by the
implementation of this workaround. Instructions on using both files are contained
within the readme file in the archive.

IMPACT: This workaround will cause Internet Explorer to no longer render folder views
for local directories, network file shares, FTP directories and web folders by
default. The ability to browse FTP directories in Internet Explorer can be restored
by clearing the "Enable Folder View for FTP Sites" option in Internet Explorer's
"Advanced" options. However, this countermeasure is known to expose another security
vulnerability that does not appear to have been fixed as of this writing:

http://lists.grok.org.uk/pipermail/full-disclosure/2003-June/005321.html

For ordinary browsing purposes, the Windows Explorer tool is unaffected by this
change. This defensive measure has been successfully implemented in at least one
commercial software product and tested on a significant scale prior to the release of
this advisory. Therefore, it is the belief of the author that potential loss of
functionality *should* be minimal. As with all measures, you are encouraged to test
the impact of this workaround prior to making any decision about deployment.

2. Prevent Automatic Navigation to Local Intranet Zone (Windows XP SP2, Windows
Server 2003 SP1)
------------------------------------------------------------------------------------------------

This workaround will prevent internet content in Internet Explorer from automatically
navigating to URLs within the Local Intranet Zone. This effectively prevents the
introduction of malicious code to the local system via the network redirector. To
implement this workaround, follow these steps:

1. In Internet Explorer's Tools menu, choose "Internet Options..."

2. Select the "Security" tab and choose "Local Intranet"

3. Click the "Custom Level" button

4. Set the "Web sites in less privileged content zone can navigate into this
zone" setting to "Disable" or "Prompt".

5. Click OK to close any dialogs and optionally, close Internet Explorer.

IMPACT: This workaround will block or prompt before allowing any navigation to LAN
resources from the Internet Zone. Direct access to LAN resources continues to
function normally. As a result of this workaround, attempts to access local intranet
content (for instance, web applications on corporate intranets) from web sites
outside of the LAN will fail or produce prompts, depending upon the chosen setting.

3. Disable Active Scripting
---------------------------

This workaround will prevent internet content from executing script that could
potentially cause the exploitation of this vulnerability. To implement this
workaround, follow these steps:

1. In Internet Explorer's Tools menu, choose "Internet Options..."

2. Select the "Security" tab and choose "Internet"

3. Click the "Custom Level" button

4. Set the "Active scripting" option to "Prompt" or "Disable".

IMPACT: This workaround will block or prompt before allowing web sites to execute any
script statement. Scripting in more-privileged zones (Local Intranet, Trusted Sites)
continues to function normally. Setting this option to "Prompt" may cause a
significant increase in the number of security prompts received while browsing and
may be ineffective in closing this vulnerability for users not capable of making an
assessment of a web site's relative trustworthiness.

Vendor URL:  www.microsoft.com/ (Links to External Site)
Cause:   Access control error, State error
Underlying OS:  Windows (Any)

Message History:   None.


 Source Message Contents

Subject:  Advisory: Internet Explorer Drag and Drop Redeux [CVE-2005-3240]

-----BEGIN PGP SIGNED MESSAGE-----
Hash: RIPEMD160

My apologies to those who are receiving this late or are otherwise
inconvenienced by the staggered release.  I had unexpected, last-minute
travel issues that interfered somewhat with today's release.

Of note since the initial drafting of the advisory is that Microsoft has
released a blog post on the MSRC blog about the vulnerability report,
which can be read here:

http://blogs.technet.com/msrc/archive/2006/02/13/419439.aspx

The technical/strategic points about the exploit that are raised in the
post are indeed accurate (though it references MS05-014, when I believe
the correct reference is MS05-008/MS05-013).  The exploit has a greater
dependence on timing than previous, related attacks.  As such,
Microsoft's decision not to include this issue in a standalone patch is
seemingly justified at this point.  However, the point of disagreement
with Microsoft remains the choice of release *timeline*.

I released the information about this issue to a trusted colleague (Gadi
Evron) for publication today, after what I felt was a reasonable time,
in light of my difficulties obtaining internet access.

Though there are disagreements between myself and Microsoft about the
nature of this vulnerability, I would like to thank Brian Schafer of the
MSRC for adhering to a high level of professionalism and technical
accuracy in that post and for continuing to work with me once it was
made clear that the issue would imminently become public.

Also of note is that there was a typo in the information I provided
originally to SecuriTeam.  The proper candidate is CVE-2005-3240, not
*3840* as was originally reported by me.  SecurityFocus has also
informed me that my original BID reservation was a casualty of a data
migration and that the proper BID associated with this vulnerability is
now BID 16352, which is public in full detail as of this writing.

There have also been some incorrect reports made to SecuriTeam that this
issue does not affect Windows XP Service Pack 2.  These reports are not
correct -- my testing during this investigation was done exclusively on
current installations of Windows 2000 and Windows XP.  These systems had
all service packs applied and all updates installed when tests were
performed.

Thanks to Gadi Evron for doing some of my bidding today and taking some
of the heat for my fat-fingers.

The final advisory, corrected with the now-accurate references is
attached with an armored-format PGP signature inline.

- --
"Social Darwinism: Try to make something idiot-proof,
nature will provide you with a better idiot."

                                -- Michael Holstein

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Version: GnuPG v1.4.2 (MingW32)
Comment: http://pgp.mit.edu:11371/pks/lookup?op=get&search=0xB5444D38

iD8DBQFD8Shufp4vUrVETTgRA/hpAJ9DobMIa4EH8otBMNlzIPK6RrMGUgCfcrrj
ZI9G00rer59rLkwI5uH0KGQ=
=DQ2a
-----END PGP SIGNATURE-----




Microsoft Internet Explorer Drag-and-Drop Redeux

I. SYNOPSIS

Affected Systems:
	* Microsoft Internet Explorer 5.01
	* Microsoft Internet Explorer 5.5
	* Microsoft Internet Explorer 6.0
		- Windows 98
		- Windows 98 Second Edition
		- Windows Millennium Edition
		- Windows 2000
		- Windows XP
		- Windows Server 2003

Risk: Medium
Impact: Potential remote code execution with some user interaction
Status: Uncoordinated Release
Author: Matthew Murphy (mattmurphy@kc.rr.com)

II. VULNERABILITY OVERVIEW

Microsoft Internet Explorer suffers from a vulnerability in its handling of certain 
drag-and-drop events.  As a result, it is possible for a malicious web site to 
predict and exploit the timing of a drag-and-drop operation such that any drag 
operation (including using scroll-bars) could potentially lead to the installation of 
arbitrary files in sensitive locations that may enable further system compromise.

III. TECHNICAL DESCRIPTION

As a result of recent updates to its drag-and-drop functionality, Internet Explorer 
now imposes a rigid set of restrictions on most drag-and-drop sources:

	* Input to the browser from other applications is not permitted.
	* Dragging an object from inside a frame is not permitted.
	* Dragging an HTML element from a top-level window will produce a security 
warning.

However, certain objects not derived from an HTML document (specifically, file 
objects within a folder view) remain draggable.  This gives rise to a potential race 
condition in the handling of user input.  If an attacker can persuade a user to drag 
any object within the top-level window that his/her site is contained in, malicious 
script can redirect these inputs to other top-level windows, potentially resulting in 
an unintended consequence such as file installation.

Proof-of-concept code has been developed that utilizes a pop-under window pointing to 
a malicious file share.  This window can be created using window.open() or other 
stealthier methods that are known to evade Internet Explorer's built-in pop-up 
blocking.  Focus is then returned to the opening window, where the user is encouraged 
to drag an object (image, link, etc.) in a seemingly "safe" fashion.

Immediately prior to this object being dragged, a mouseOver event is triggered that 
enables the attacker to (with a varying degree of success) predict the imminent drag 
attempt.  The pop-under can then be returned to focus by way of a window.blur() 
executed in the current window.  If the timing of the transition is accurate to a 
margin of error within a user's reaction time threshold, the user will unwittingly 
initiate a drag of a file from the pop-under instead of the object originally used as 
a lure by the attacker.

As soon as it transfers focus, the window with the original interactive content may 
set a timer (via window.setTimeout()) that returns focus to the window with a simple 
window.focus() call.  After a split-second delay, focus is returned to the 
interactive window.  At this point, on-demand alteration of CSS attributes can be 
used to display previously-hidden objects (such as inline frames).  These objects 
serve as "drop target" windows and will initiate the copying of the file dropped from 
the (presumably malicious) pop-under window.

While Internet Explorer blocks hiding or resizing of certain "suspect" objects 
(IFRAMEs, for instance), so-called container objects (DIV, SPAN, etc.) suffer no such 
restrictions, even when they contain one of the objects in the former category.  The 
proof-of-concept code as developed simply stores a full-screen inline frame in a 
container initially marked with the "hidden" visibility style.

The pop-under window, in this instance, would be a folder on a malicious server.  
This could be accessed via SMB (\\HOSTILESERVER\SHARE), FTP 
(ftp://hostileserver/somedirectory) or even HTTP (web folders) using certain link 
behaviors in combination with the click() method of a hyperlink object.  In the third 
case, the pop-under would be targeted to an HTML document initally, which would then 
open the web folder containing hostile content.

The path to the drop target (the hidden frame in the original window) requires a 
little more creativity.  Particularly in Windows XP Service Pack 2, Microsoft has 
done a fairly good job of locking down access to local resources.  The most 
interesting vector for the purposes of this attack is via the network redirector.  By 
using the IP address or machine name of the local system (typically obtainable via 
any number of means), such as:

	\\MACHINENAME\share

It becomes possible to access resources offered by the network redirector on the 
local system.  Of most interest is the "Scheduled Tasks" folder:

	\\MACHINENAME\Scheduled Tasks

Items dropped into this folder execute automatically at a system-determined time (3 
AM local time in tests on Windows XP Professional Service Pack 2) each day as the 
user dropping the file.  Also of interest are common shares such as the 
administrative shares (C$, D$, etc.) and typical share names like "SharedDocs" on 
Windows XP.  In most cases, this is at least a partial functional equivalent to local 
file system access and is not subject to zone restrictions, even on Windows XP 
Service Pack 2.

IV. IMPACT

A malicious web site, with a minimum of social engineering, may be able to compromise 
user systems by triggering an unintended installation of malicious software.  Typical 
defense-in-depth measures may mitigate this issue.  For those who run Internet 
Explorer with administrative privileges, the impact of any successful exploitation is 
complete control of the affected system.  A malicious web site could install software 
that would add or delete privileged user accounts, alter, destroy or disclose the 
content of personal or otherwise sensitive files, record personal information or any 
number of other activities.

Users who do not browse with such high levels of privilege would be at a 
significantly reduced risk from exploitation of this vulnerability.  In the case of a 
user with limited privileges, this vulnerability could only be exploited by an 
attacker to install software that executes with the privileges of that user.

V. WORKAROUNDS

The following workarounds are believed at the time of this writing to be effective 
against the exploitation of this vulnerability in some form:

1. Set a Kill Bit on the Shell.Explorer Control
-----------------------------------------------

Setting a kill bit on this control will prevent Internet Explorer from displaying the 
rich folder view interface that gives rise to this attack.  For more information 
about setting kill bits, please see Microsoft Knowledge Base Article 240797:

	http://support.microsoft.com/kb/240797

The CLSID of this component as deployed on Windows XP is:

  	{8856F961-340A-11D0-A96B-00C04FD705A2}

Tools to automate the process of setting this kill bit have been provided at:

	http://student.missouristate.edu/m/matthew007/tools/shellkill.zip
	PGP signature: http://student.missouristate.edu/m/matthew007/tools/shellkill.zip.asc

Included in this archive are an Administrative Template (.adm) and a VBScript file 
(.vbs) which implement this setting.  The Administrative Template also allows an 
administrator to work around a specific case of functionality loss caused by the 
implementation of this workaround.  Instructions on using both files are contained 
within the readme file in the archive.

IMPACT: This workaround will cause Internet Explorer to no longer render folder views 
for local directories, network file shares, FTP directories and web folders by 
default.  The ability to browse FTP directories in Internet Explorer can be restored 
by clearing the "Enable Folder View for FTP Sites" option in Internet Explorer's 
"Advanced" options.  However, this countermeasure is known to expose another security 
vulnerability that does not appear to have been fixed as of this writing:

	http://lists.grok.org.uk/pipermail/full-disclosure/2003-June/005321.html

For ordinary browsing purposes, the Windows Explorer tool is unaffected by this 
change.  This defensive measure has been successfully implemented in at least one 
commercial software product and tested on a significant scale prior to the release of 
this advisory.  Therefore, it is the belief of the author that potential loss of 
functionality *should* be minimal.  As with all measures, you are encouraged to test 
the impact of this workaround prior to making any decision about deployment.

2. Prevent Automatic Navigation to Local Intranet Zone (Windows XP SP2, Windows 
Server 2003 SP1)
------------------------------------------------------------------------------------------------

This workaround will prevent internet content in Internet Explorer from automatically 
navigating to URLs within the Local Intranet Zone.  This effectively prevents the 
introduction of malicious code to the local system via the network redirector.  To 
implement this workaround, follow these steps:

	1. In Internet Explorer's Tools menu, choose "Internet Options..."

	2. Select the "Security" tab and choose "Local Intranet"

	3. Click the "Custom Level" button

	4. Set the "Web sites in less privileged content zone can navigate into this 
zone" setting to "Disable" or "Prompt".

	5. Click OK to close any dialogs and optionally, close Internet Explorer.

IMPACT: This workaround will block or prompt before allowing any navigation to LAN 
resources from the Internet Zone.  Direct access to LAN resources continues to 
function normally.  As a result of this workaround, attempts to access local intranet 
content (for instance, web applications on corporate intranets) from web sites 
outside of the LAN will fail or produce prompts, depending upon the chosen setting.

3. Disable Active Scripting
---------------------------

This workaround will prevent internet content from executing script that could 
potentially cause the exploitation of this vulnerability.  To implement this 
workaround, follow these steps:

	1. In Internet Explorer's Tools menu, choose "Internet Options..."

	2. Select the "Security" tab and choose "Internet"

	3. Click the "Custom Level" button

	4. Set the "Active scripting" option to "Prompt" or "Disable".

IMPACT: This workaround will block or prompt before allowing web sites to execute any 
script statement.  Scripting in more-privileged zones (Local Intranet, Trusted Sites) 
continues to function normally.  Setting this option to "Prompt" may cause a 
significant increase in the number of security prompts received while browsing and 
may be ineffective in closing this vulnerability for users not capable of making an 
assessment of a web site's relative trustworthiness.

VI. MITIGATION RECOMMENDATIONS

1. Limit Viewing to Trusted Web Sites
-------------------------------------

In some situations, browsing can be successfully limited to only trustworthy sites 
without significant loss of productivity.  Users should be extremely cautious while 
browsing unknown or untrusted web sites, as such web sites are often able to 
introduce hostile code.

2. Run Exposed Applications With Reduced Privilege
--------------------------------------------------

Users who log on interactively without the privileges of powerful groups such as the 
"Administrators" or "Power Users" groups are at a much lower risk of damage from 
successful exploitation of software vulnerabilities in client applications.  This 
mitigation step greatly reduces the likelihood of a successful malware installation 
if this vulnerability is exploited.

VII. VENDOR RESPONSE

Microsoft was informed of this vulnerability on August 3, 2005.  Currently, the 
company has no plans to issue a security update to correct this vulnerability.  Fixes 
for this issue are scheduled to be included in Service Pack 2 of Windows Server 2003 
and Service Pack 3 of Windows XP.  Of particular note is that Windows 2000 users will 
*NOT* receive an update to correct this vulnerability.

Microsoft's internal risk-assessment concluded that this issue was not sufficiently 
serious to be fixed in a security bulletin.  This conclusion appears fundamentally 
inconsistent with the way related issues were handled by Microsoft.  In particular, 
the drag-and-drop vulnerability patched by MS05-013 received an "Important" rating.

I disagree with the technical conclusion behind Microsoft's decision and I further 
find the timeframe of delivery and deployment for maintenance releases to be largely 
unsuitable for security fixes of any significant magnitude.  I find the harm this 
decision could potentially inflict upon down-level users (most importantly, users of 
Windows 2000) to be unjustified by the technical concern Microsoft has raised to me.  
Microsoft also rejected a request that it consider the issue for inclusion in a later 
security update as a "Moderate" risk issue.

Due to Microsoft's noncommittal and generally unimpressive response to the issue, 
this advisory is being issued to inform users of this vulnerability such that 
defensive action may be taken as desired.

VIII. REFERENCES/STANDARDS

* CVE

The MITRE Common Vulnerabilities and Exposures (CVE) project has assigned the name 
CVE-2005-3840 to this issue.  Status information and related references for this 
candidate may be found at:

	http://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2005-3840

* OSVDB

The Open Source Vulnerability Database (OSVDB) project has assigned OSVDB 
vulnerability ID #2707 to this issue.  Information will be available shortly after 
the publication of this advisory at the following URL:

	http://www.osvdb.org/displayvuln.php?osvdb_id=2707

* SecurityTracker

SecurityTracker has pre-assigned an alert number in its internal database to 
reference this issue.  Information will be available shortly after the publication of 
this advisory at the following URL:

	http://www.securitytracker.com/id?1015049

* SecurityFocus

SecurityFocus has pre-assigned BugTraq ID #15089 to reference this issue.  
Information will be available shortly after the publication of this advisory at the 
following URL:

	http://www.securityfocus.com/bid/15089

IX. ACKNOWLEDGEMENTS

* The Administrative Template file supplied in the workaround ZIP was authored by 
Steven Platt.

X. CONTACT

The author may be contacted via e-mail at mattmurphy@kc.rr.com

XI. LEGAL

This document is believed accurate based upon information available at the time it 
was written.  However, the information offered is offered in an AS-IS condition, 
without warranty.  By acting upon this information in any way you accept all 
responsibility for damage that may occur as a result.

This document may be reproduced in whole without limitation and in part provided that 
a full copy of the original document is readily accessible and the author of the 
document is duly acknowledged.
 
 


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