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Cisco Security Advisory: 
Local Privilege Escalation Vulnerabilities in Cisco VPN Client

Advisory ID: cisco-sa-20070815-vpnclient

http://www.cisco.com/warp/public/707/cisco-sa-20070815-vpnclient.shtml

Revision 1.0

For Public Release 2007 August 15 1600 UTC (GMT)

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

Summary
=======

Two vulnerabilities exist in the Cisco VPN Client for Microsoft Windows
that may allow unprivileged users to elevate their privileges to those of
the LocalSystem account.

A workaround exists for one of the two vulnerabilities disclosed in this
advisory.

Cisco has made free software available to address these vulnerabilities
for affected customers.

This advisory is posted at 
http://www.cisco.com/warp/public/707/cisco-sa-20070815-vpnclient.shtml.

Affected Products
=================

Vulnerable Products
+------------------

The vulnerabilities described in this document apply to the Cisco VPN
Client on the Microsoft Windows platform. The affected versions are
included in the following table:

+----------------------------------------------------------------+
|     Vulnerability Name      |     Versions     | Cisco Bug ID  |
|                             |     affected     |               |
|-----------------------------+------------------+---------------|
| 1. Local Privilege          | All versions up  | CSCse89550    |
| Escalation Through          | to but not       |               |
| Microsoft Windows Dial-Up   | including        |               |
| Networking Interface        | 4.8.02.0010      |               |
|-----------------------------+------------------+---------------|
| 2. Local Privilege          | All versions up  | CSCsj00785    |
| Escalation Through Default  | to but not       |               |
| cvpnd.exe File Permissions  | including        |               |
|                             | 5.0.01.0600      |               |
+----------------------------------------------------------------+

Note: The VPN Client for Windows software is distributed as both a
Microsoft Installer (MSI) package and an InstallShield (IS) package. Only
the MSI package for version 5.0.01.0600 of the VPN Client contains the fix
for the "Local Privilege Escalation Through Default cvpnd.exe File
Permissions" vulnerability. The IS package does not contain the fix for
that vulnerability and has been removed from http://www.cisco.com.
Customers who have downloaded and installed the IS package for version
5.0.01.0600 of the VPN Client will need to apply the workaround listed in
the Workarounds section of this advisory or migrate to the MSI package to
address these vulnerabilities.

Products Confirmed Not Vulnerable
+--------------------------------

Versions of the Cisco VPN Client for platforms other than Microsoft
Windows are not affected by these vulnerabilities. Specifically, the
following versions of the Cisco VPN client are not affected:

  * Cisco VPN Client for Solaris
  * Cisco VPN Client for Linux
  * Cisco VPN Client for Macintosh (Mac OS Classic and Mac OS X)

The Cisco AnyConnect VPN Client is not affected by these vulnerabilities.

No other Cisco products are known to be affected by the vulnerabilities
described in this advisory.

Determining the Cisco VPN Client Version
+---------------------------------------

To determine which version of the Cisco VPN Client is running on a
Microsoft Windows machine, follow the following steps:

 1. Select "Programs->Cisco Systems VPN Client->VPN Client" from the Start
    menu. This action will open the Cisco VPN Client graphical user
    interface.
 2. Select the option "About VPN Client..." from the "Help" menu. This
    menu option will display a dialog box that contains text similar to
    "Cisco Systems VPN Client Version 4.8.01.0300."

Note: By default, the "Cisco Systems VPN Client" folder is located in the
"Programs" sub-menu of the Windows Start menu. The system administrator
may have chosen to use a different name or location.

Alternatively, the Cisco VPN Client version information can be obtained
from a Microsoft Windows Command Prompt using the "vpnclient.exe version"
command. For example:

    C:\Program Files\Cisco Systems\VPN Client>vpnclient version
    4.8.01.0300


Details
=======

The Cisco VPN Client is a software solution for the Microsoft Windows, Sun
Solaris, Linux, and Apple MacOS Classic and MacOS X operating systems. It
allows users to establish IPSec VPN tunnels to Cisco VPN-capable devices,
such as Cisco IOS routers, the PIX Security Appliance, the VPN 3000 Series
Concentrators, and the ASA 5500 Series Adaptive Security Appliances.

Two vulnerabilities exist in the Cisco VPN Client for Microsoft Windows
that may allow local, unprivileged users to elevate their privileges.

Note: The following vulnerabilities are different from the vulnerability
that was detailed in the Cisco Security Advisory for the Cisco VPN Client
for Windows available at 
http://www.cisco.com/warp/public/707/cisco-sa-20060524-vpnclient.shtml.


1. Local Privilege Escalation Through Microsoft Windows Dial-Up Networking
Interface


Unprivileged users can elevate their privileges to those of the
LocalSystem account by enabling the Start Before Logon (SBL) feature
and configuring a VPN profile to use the Microsoft Dial-Up Networking
interface. When these two settings are enabled and configured
concurrently, the Cisco VPN Client Graphical User Interface (GUI)
will be available in the Windows logon screen. It should be noted
that configuring these two settings does not require the user to have
administrative privileges.

- From the Windows logon screen, users can leverage a VPN profile that is
configured to utilize Microsoft dial-up networking to launch a dial-up
networking dialog box. This action may allow users to elevate their
privileges.

This vulnerability has been addressed by requiring that the configuration
option "Allow launching of third party applications before logon," which
is located in the "Windows Logon Properties" dialog box (available under
Options-> Windows Logon Properties...), be enabled to use, from the
Windows logon screen, a VPN profile that is configured for Microsoft
Dial-Up Networking.

Note: Enabling "Allow launching of third party applications before
logon" can itself raise some security issues; by design, only users with
administrative rights can enable this option.

This vulnerability is documented in Cisco Bug ID CSCse89550 

Additional information on the SBL feature can be found at 
http://www.cisco.com/en/US/docs/security/vpn_client/cisco_vpn_client/vpn_client46/win/user/guide/vc7.html#wp1301567
For information about the LocalSystem account and its privileges, please
refer to http://msdn2.microsoft.com/en-us/library/ms684190.aspx


2. Local Privilege Escalation Through Default cvpnd.exe File Permissions


Unprivileged users can execute arbitrary programs that run with the
privileges of the LocalSystem account by replacing the Cisco VPN Service
executable with arbitrary executables. This vulnerability exists because
the default file permissions assigned during installation to cvpnd.exe
(the executable for the Cisco VPN Service) allow unprivileged, interactive
users to replace cvpnd.exe with any file.

Because the Cisco VPN Service is a Windows service running with
LocalSystem privileges, unprivileged users can easily elevate their
privileges.

It is possible to work around this vulnerability without a software
upgrade. Please refer to the Workarounds section of this advisory.

This vulnerability is documented in Cisco Bug ID CSCsj00785 

Vulnerability Scoring Details
+----------------------------

Cisco is providing scores for the vulnerabilities in this advisory based
on the Common Vulnerability Scoring System (CVSS). The CVSS scoring in
this Security Advisory is done in accordance with CVSS version 2.0.

Cisco will provide a base and temporal score. Customers can then compute
environmental scores to assist in determining the impact of the
vulnerability in individual networks.

Cisco PSIRT will set the bias in all cases to normal. Customers are
encouraged to apply the bias parameter when determining the environmental
impact of a particular vulnerability.

CVSS is a standards-based scoring method that conveys vulnerability
severity and helps determine urgency and priority of response.

Cisco has provided an FAQ to answer additional questions regarding CVSS at

http://www.cisco.com/web/about/security/intelligence/cvss-qandas.html.

Cisco has also provided a CVSS calculator to help compute the
environmental impact for individual networks at

http://intellishield.cisco.com/security/alertmanager/cvss

Local Privilege Escalation Through Microsoft Windows Dial-Up Networking 
Interface (CSCse89550)

CVSS Base Score - 6.8 
    Access Vector -            Local
    Access Complexity -        Low
    Authentication -           Single
    Confidentiality Impact -   Complete
    Integrity Impact -         Complete
    Availability Impact -      Complete
    Impact Bias -              Normal

CVSS Temporal Score - 5.9     
    Exploitability -           High
    Remediation Level -        Official-Fix
    Report Confidence -        Confirmed



Local Privilege Escalation Through Default cvpnd.exe File Permissions 
(CSCsj00785)

CVSS Base Score - 6.8 
    Access Vector -            Local
    Access Complexity -        Low
    Authentication -           Single
    Confidentiality Impact -   Complete
    Integrity Impact -         Complete
    Availability Impact -      Complete
    Impact Bias -              Normal

CVSS Temporal Score - 5.9     
    Exploitability -           High
    Remediation Level -        Official-Fix
    Report Confidence -        Confirmed


Impact
======

Successful exploitation of any the vulnerabilities described in this
document may result in a valid, unprivileged user gaining full control of
the system.

Software Version 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.

Each row of the Cisco VPN Client software table (below) describes one of
the vulnerabilities described in this document. For each vulnerability,
the earliest possible release that contains the fix (the "First Fixed
Release") and the anticipated date of availability for each are listed in
the "First Fixed Release" column. A device running a release that is
earlier than the release in a specific column (less than the First Fixed
Release) is known to be vulnerable. The release should be upgraded at
least to the indicated release or a later version (greater than or equal
to the First Fixed Release label).

+----------------------------------------------------------------+
|                 Vulnerability                  |  First Fixed  |
|                                                |    Release    |
|------------------------------------------------+---------------|
| 1. Local Privilege Escalation Through          | 4.8.02.0010   |
| Microsoft Windows Dial-Up Networking Interface | (MSI and IS   |
| (CSCse89550)                                   | packages)     |
|------------------------------------------------+---------------|
| 2. Local Privilege Escalation Through Default  | 5.0.01.0600   |
| cvpnd.exe File Permissions (CSCsj00785)        | (MSI package  |
|                                                | only)         |
+----------------------------------------------------------------+

Note: The VPN Client for Windows software is distributed as both a
Microsoft Installer (MSI) package and an InstallShield (IS) package. Only
the MSI package for version 5.0.01.0600 of the VPN Client contains the fix
for the "Local Privilege Escalation Through Default cvpnd.exe File
Permissions" vulnerability. The IS package does not contain the fix for
that vulnerability and has been removed from http://www.cisco.com.
Customers who have previously downloaded and installed the IS package for
version 5.0.01.0600 of the VPN Client will need to apply the workaround
listed in the Workarounds section of this advisory or migrate to the MSI
package to address these vulnerabilities.

Note: Customers who want to deploy a software version containing fixes for
the two vulnerabilities disclosed in this advisory should deploy the MSI
package for v5.0.01.0600 of the VPN Client.

The Cisco VPN Client for Windows is available for download from the
following location on cisco.com:

http://www.cisco.com/pcgi-bin/tablebuild.pl/windows?psrtdcat20e2

Please note that security fixes are not applied to older versions of the
Cisco VPN Client for Windows software. Customers looking for a version
containing fixes for all published vulnerabilities affecting the Cisco VPN
Client for Windows should download and install the latest MSI package
available from the previously listed URL.

Workarounds
===========

1. Local Privilege Escalation Through Microsoft Windows Dial-Up Networking
Interface

There are no workarounds for this vulnerability.

2. Local Privilege Escalation Through Default cvpnd.exe File Permissions

An effective workaround for this vulnerability is to revoke access rights
for NT AUTHORITY\INTERACTIVE from cvpnd.exe. For example:

    C:\Program Files\Cisco Systems\VPN Client>cacls cvpnd.exe /E /R "NT AUTHORITY\INTERACTIVE"


Note: Windows Vista includes icacls, an updated partial replacement for
cacls. More information about icacls can be found at 
http://www.microsoft.com/technet/technetmag/issues/2007/07/SecurityWatch/default.aspx 

Obtaining Fixed Software
========================

Cisco will make free software available to address these vulnerabilities
for affected customers. This advisory will be updated as fixed software
becomes available. 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-alert@cisco.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: tac@cisco.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 vulnerabilities described in this advisory.

The "Local Privilege Escalation Through Microsoft Windows Dial-Up
Networking Interface" vulnerability (CSCse89550) was reported to Cisco by
a customer.

The "Local Privilege Escalation Through Default cvpnd.exe File
Permissions" vulnerability (CSCsj00785) was reported to Cisco by Dominic
Beecher of Next Generation Security Software Ltd. Dominic also provided a
viable workaround for this vulnerability. Cisco would like to thank
Dominic Beecher and Next Generation Security Software Ltd. for reporting
this vulnerability and for working with us towards a coordinated
disclosure of the vulnerability.

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/cisco-sa-20070815-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-announce@cisco.com
  * first-teams@first.org
  * bugtraq@securityfocus.com
  * vulnwatch@vulnwatch.org
  * cisco@spot.colorado.edu
  * cisco-nsp@puck.nether.net
  * full-disclosure@lists.grok.org.uk
  * comp.dcom.sys.cisco@newsgate.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
================

+----------------------------------------------------------------+
| Revision 1.0   | 2007-August-15   | Initial public release     |
+----------------------------------------------------------------+

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/products/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/go/psirt.

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All contents are Copyright 2006-2007 Cisco Systems, Inc. All rights
reserved. 
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Updated: May 25, 2007                                   Document ID: 91923

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