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Cisco Security Advisory:
Windows VPN Client Local Privilege Escalation Vulnerability
Document ID: 70332
Advisory ID: cisco-sa-20060524-vpnclient
http://www.cisco.com/warp/public/707/cisco
-sa-20060524-vpnclient.shtml
Revision 2.0
Last Updated 2006 July 27 2000 UTC (GMT)
For Public Release 2006 May 24 1600 UTC (GMT)
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Contents
========
Summary
Affected Products
Details
Impact
Software Versions and Fixes
Workarounds
Obtaining Fixed Software
Exploitation and Public Announcements
Status of This Notice: FINAL
Distribution
Revision History
Cisco Security Procedures
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Summary
=======
The Cisco VPN Client for Windows is affected by a local
privilege
escalation vulnerability that allows non-privileged users to
gain
administrative privileges.
A user needs to authenticate and start an interactive
Windows session
to be able to exploit this vulnerability.
Cisco has made free software available to address this
vulnerability
for affected customers. There is a workaround available to
mitigate the
effects of the vulnerability.
This advisory is posted at
http://www.cisco.com/warp/public/707/cisc
o-sa-20060524-vpnclient.shtml.
Affected Products
=================
Vulnerable Products
+------------------
The following versions of the Cisco VPN Client for Windows
(excluding
Windows 9x users) are affected:
* 2.x
* 3.x
* 4.0.x
* 4.6.x
* 4.7.x with the exception of version 4.7.00.0533 (see
below in
Products Confirmed Not Vulnerable.)
* 4.8.00.x
Products Confirmed Not Vulnerable
+--------------------------------
All other versions of Cisco VPN Client that are based on an
operating
system other than Microsoft Windows are not affected by this
vulnerability. These include:
* Any version of the Cisco VPN Client for Solaris
* Any version of the Cisco VPN Client for Linux
* Any version of the Cisco VPN Client for Macintosh (MacOS
X and
MacOS Classic)
Cisco VPN Client for Windows version 4.8.01.x and later are
not
affected by this vulnerability.
In addition, due to a regression, version 4.7.00.0533 of the
Cisco VPN
Client for Windows is not affected, even though other 4.7.x
are
affected. Users running version 4.7.00.0533 of the Cisco VPN
Client for
Windows do not need to upgrade to version 4.8.01 or later to
be
protected from this vulnerability.
No other Cisco products are currently known to be affected
by this
vulnerability.
Determining the Cisco VPN Client Version
+---------------------------------------
In order to determine which version of the Cisco VPN Client
is running
on the Microsoft Windows machine, open the Cisco VPN Client
graphical
user interface by selecting "Programs->Cisco
Systems VPN Client->VPN
Client" from the Start menu and then select the option
"About VPN
Client..." from the "Help" menu. This will
display a dialog box
containing text similar to "Cisco Systems VPN Client
Version 4.0.5(Rel)
". Please note that the location of the "Cisco
Systems VPN Client"
folder mentioned above in Windows' Start menu is where the
program is
installed by default; your system administrator may have
chosen to use
a different name or location.
Details
=======
The Cisco VPN Client is a software solution for the Sun
Solaris, Apple
MacOS Classic and MacOS X, Linux and Microsoft Windows
operating
systems that allows users running these operating systems to
establish
IPSec VPN tunnels to Cisco VPN-capable devices like Cisco
IOS routers,
the PIX Security Appliance, the VPN 3000 Series
Concentrators, and the
ASA 5500 Series Adaptive Security Appliances.
A vulnerability in the Cisco VPN Client for Windows
graphical user
interface (GUI), also known as the "VPN client
dialer", can be
exploited to elevate user privileges and obtain
LocalSystem-equivalent
privileges.
The vulnerability occurs when the Start Before Logon (SBL)
feature is
enabled on the Cisco VPN Client. This feature can be enabled
by
unprivileged users from the Cisco VPN Client GUI. Once this
feature is
enabled, the user will see a Cisco VPN Client GUI in the
Windows logon
screen. When the user accesses Cisco VPN Client help in this
GUI with
the F1 key, the Cisco VPN Client spawns a web browser
process. Since no
user has logged in yet, the Cisco VPN Client is running with
LocalSystem privileges, and therefore so will the spawned
web browser
process. After the logon sequence is completed, the user has
a web
browser window on the desktop, running with LocalSystem
privileges.
Additional information on the SBL feature can be found at:
http://www.cisco.com/unive
rcd/cc/td/doc/product/vpn/client/4_6/ugwin/vc7.htm#wp1301567
This issue is not related to any known issues in Microsoft
Windows
itself.
This vulnerability is documented by Cisco Bug ID CSCsd79265
For information about local system level privileges, please
refer to:
* The LocalSystem Account
http://msdn
.microsoft.com/library/default.asp?url=/library/en-us/dllpro
c/base/localsystem_account.asp
Impact
======
Successful exploitation of the vulnerability may result in a
normal
user or attacker gaining full control of the system, evading
any
controls put in place by the Windows system administrator.
Software Versions and Fixes
===========================
When considering software upgrades, also consult
http://www.cisco.com/go
/psirt and any subsequent advisories to
determine exposure and a complete upgrade solution.
In all cases, customers should exercise caution to be
certain the
devices to be upgraded contain sufficient memory and that
current
hardware and software configurations will continue to be
supported
properly by the new release. If the information is not
clear, contact
the Cisco Technical Assistance Center ("TAC") or
your contracted
maintenance provider for assistance.
This vulnerability is fixed in version 4.8.01.0300 of the
Cisco VPN
Client for Windows, which can be downloaded from the
following
location:
h
ttp://www.cisco.com/pcgi-bin/tablebuild.pl/windows
For information on how to upgrade the Cisco VPN Client,
including
automatic upgrades, please refer to the following chapter of
the VPN
Client Administrator Guide: Updating VPN Client Software.
Workarounds
===========
A workaround for this vulnerability is to prevent the
LocalSystem
account (also known as "SYSTEM") from launching
the application
associated with files with the ".html"
extension. After applying this
workaround, pressing the F1 key on the Cisco VPN Client GUI
in the
Windows logon screen has no effect.
This can be accomplished by attaching an Access Control List
(ACL)
entry to the Windows registry keys
HKEY_LOCAL_MACHINE\Software\Classes\.html and
HKEY_CLASSES_ROOT\.html
so that the NT-AUTHORITY\SYSTEM account is denied all
access to that key.
The following example uses the tool RegDACL (Copyright(c)
1999-2001
Frank Heyne Software), available from
http://ww
w.heysoft.de/Frames/f_sw_rt_en.htm , to apply the
Windows
registry ACL mentioned above:
C:\>regdacl HKLM\Software\Classes\.html /DGS:F
RegDACL 5.1 - Permissions Manager for Registry keys for
Windows NT 4 and above
Copyright (c) 1999-2001 Frank Heyne Software (http://www.heysoft.de)
This program is Freeware, use it on your own risk!
Denying F access for predefined group "System"
- adding new ACCESS DENY entry
- removing existing entry
C:\>regdacl HKCR\.html /DGS:F
RegDACL 5.1 - Permissions Manager for Registry keys for
Windows NT 4 and above
Copyright (c) 1999-2001 Frank Heyne Software (http://www.heysoft.de)
This program is Freeware, use it on your own risk!
Denying F access for predefined group "System"
- adding new ACCESS DENY entry
- removing existing entry
C:\>
Another tool that can be used to accomplish the same is the
Regini.exe
utility that comes with several versions of the Windows
Resource Kit.
For more information on how to use Regini.exe, please visit
the
following Microsoft Knowledge Base article:
* How to Use Regini.exe to Set Permissions on Registry
Keys
http://supp
ort.microsoft.com/?kbid=237607
Manually editing the Windows registry with RegEdit.exe will
also work,
but this method does not scale when the operation needs to
be performed
on a large number of machines.
While Cisco has tested the above workaround in Cisco's test
environment, the effectiveness and impact of any workaround
is
dependent on each customer's particular environment.
Customers electing
to apply any workaround (rather than upgrading to an updated
version of
the Cisco VPN Client) are encouraged to test such workaround
thoroughly
to ensure, among other things, that it does not negatively
impact any
other applications that may rely on applicable functionality
(e.g., the
ability of the LocalSystem account to launch HTML files from
any
application).
Obtaining Fixed Software
========================
Cisco has made free software available to address this
vulnerability
for affected customers. Prior to deploying software,
customers should
consult their maintenance provider or check the software for
feature
set compatibility and known issues specific to their
environment.
Customers may only install and expect support for the
feature sets they
have purchased. By installing, downloading, accessing or
otherwise
using such software upgrades, customers agree to be bound by
the terms
of Cisco's software license terms found at
http://www.cisco.com/public/sw-license-agreement.html,
or as otherwise
set forth at Cisco.com Downloads at
http://www.cisco.com/public/sw-center/sw-usingswc.shtml.
Do not contact either "psirt cisco.com" or
"security-alertcisco.com"
for software upgrades.
Customers with Service Contracts
+-------------------------------
Customers with contracts should obtain upgraded software
through their
regular update channels. For most customers, this means that
upgrades
should be obtained through the Software Center on Cisco's
worldwide
website at http://www.cisco.com.
Customers using Third-party Support Organizations
+------------------------------------------------
Customers whose Cisco products are provided or maintained
through prior
or existing agreement with third-party support organizations
such as
Cisco Partners, authorized resellers, or service providers
should
contact that support organization for guidance and
assistance with the
appropriate course of action in regards to this advisory.
The effectiveness of any workaround or fix is dependent on
specific
customer situations such as product mix, network topology,
traffic
behavior, and organizational mission. Due to the variety of
affected
products and releases, customers should consult with their
service
provider or support organization to ensure any applied
workaround or
fix is the most appropriate for use in the intended network
before it
is deployed.
Customers without Service Contracts
+----------------------------------
Customers who purchase direct from Cisco but who do not hold
a Cisco
service contract and customers who purchase through
third-party vendors
but are unsuccessful at obtaining fixed software through
their point of
sale should get their upgrades by contacting the Cisco
Technical
Assistance Center (TAC). TAC contacts are as follows.
* +1 800 553 2447 (toll free from within North America)
* +1 408 526 7209 (toll call from anywhere in the world)
* e-mail: taccisco.com
Have your product serial number available and give the URL
of this
notice as evidence of your entitlement to a free upgrade.
Free upgrades
for non-contract customers must be requested through the
TAC.
Refer to http://www.cisco.com/warp/public/687/Directory/DirTAC
.shtml
for additional TAC contact information, including special
localized
telephone numbers and instructions and e-mail addresses for
use in
various languages.
Exploitation and Public Announcements
=====================================
The Cisco PSIRT is not aware of any public announcements or
malicious
use of the vulnerability described in this advisory.
This vulnerability was independently reported to Cisco by
Andrew
Christensen from FortConsult and by Johan Ronkainen. Cisco
would like
to thank them for working with us towards coordinated
disclosure of
this vulnerability.
Applying an ACL to the HKCR\.html registry key in order to
prevent the
SYSTEM account from being able to launch a web browser was
suggested to
Cisco Systems by Johan Ronkainen.
FortConsult's advisory is available at the following
location:
http://www.fortconsult.net/images/pdf/cisco_advi
sory_may2006.pdf
Status of This Notice: FINAL
============================
THIS DOCUMENT IS PROVIDED ON AN "AS IS" BASIS
AND DOES NOT IMPLY ANY
KIND OF GUARANTEE OR WARRANTY, INCLUDING THE WARRANTIES OF
MERCHANTABILITY OR FITNESS FOR A PARTICULAR USE. YOUR USE OF
THE
INFORMATION ON THE DOCUMENT OR MATERIALS LINKED FROM THE
DOCUMENT IS AT
YOUR OWN RISK. CISCO RESERVES THE RIGHT TO CHANGE OR UPDATE
THIS
DOCUMENT AT ANY TIME.
A stand-alone copy or Paraphrase of the text of this
document that
omits the distribution URL in the following section is an
uncontrolled
copy, and may lack important information or contain factual
errors.
Distribution
============
This advisory is posted on Cisco's worldwide website at
http://www.cisco.com/warp/public/707/cisc
o-sa-20060524-vpnclient.shtml.
In addition to worldwide web posting, a text version of this
notice is
clear-signed with the Cisco PSIRT PGP key and is posted to
the
following e-mail and Usenet news recipients.
* cust-security-announcecisco.com
* first-teamsfirst.org
* bugtraqsecurityfocus.com
* vulnwatchvulnwatch.org
* ciscospot.colorado.edu
* cisco-nsppuck.nether.net
* full-disclosurelists.grok.org.uk
* comp.dcom.sys.cisconewsgate.cisco.com
Future updates of this advisory, if any, will be placed on
Cisco's
worldwide website, but may or may not be actively announced
on mailing
lists or newsgroups. Users concerned about this problem are
encouraged
to check the above URL for any updates.
Revision History
================
+-----------------------------------------------------------
--------------+
| | | * Added full details about
the |
| | | vulnerability (see the
Details |
| | | section.)
|
| | | * Provided possible
workarounds (see |
| Revision 2.0 | 2006-July-27 | the Workarounds
section). |
| | | * Added a link to
FortConsult's |
| | | advisory
|
| | | * Changed "Status of
this Notice" from |
| | | INTERIM to FINAL.
|
|--------------+--------------+-----------------------------
--------------|
| | |
|
| Revision 1.0 | 2006-May-24 | Initial public release.
|
| | |
|
+-----------------------------------------------------------
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Cisco Security Procedures
Complete information on reporting security vulnerabilities
in Cisco
products, obtaining assistance with security incidents, and
registering
to receive security information from Cisco, is available on
Cisco's
worldwide website at
http://www.cisco.com/en/US/produ
cts/products_security_vulnerability_policy.html.
This includes instructions for press inquiries regarding
Cisco security
notices. All Cisco security advisories are available at
http://www.cisco.com/g
o/psirt.
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All contents are Copyright 1992-2006 Cisco Systems, Inc. All
rights reserved.
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Updated: Jul 27, 2006
Document ID: 70332
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