Cisco Security Advisory

Advisory ID: cisco-sa-20070815-vpnclient

http://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20070815-vpnclient

Revision 1.3

Last Updated  2011 March 24 17:00  UTC (GMT)

For Public Release 2007 August 15 16:00  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://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20070815-vpnclient.

Note: Releases 5.0.7.0240 (beta release) and 5.0.7.0290 (official release) of the 64-bit version of the Cisco VPN Client had a regression in the fix for the vulnerability "Local Privilege Escalation Through Default cvpnd.exe File Permissions". Release 5.0.7.0440 of the 64-bit Cisco VPN Client fixes this regression. 32-bit versions of the Cisco VPN Client did not have this regression.

Affected Products

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://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20060524-vpnclient.

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 ( registered customers only) .

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 ( registered customers only) .

Note: Releases 5.0.7.0240 (a beta release) and 5.0.7.0290 (an official release) of the 64-bit version of the Cisco VPN Client had a regression in the fix for CSCsj00785 ( registered customers only) and are also affected. Release 5.0.7.0440 of the 64-bit Cisco VPN Client fixes this regression. 32-bit versions of the Cisco VPN Client did not have this regression. The fix for the regression is documented in Cisco Bug ID CSCtn50645 ( registered customers only) .

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

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

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

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 .

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

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).

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.

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.

Note: It has been reported that upgrades to version 5.0.01.0600 of the Cisco VPN Client in non-English versions of Microsoft Windows may fail. This issue is being tracked by Cisco Bug ID CSCsj89801, and Cisco has made available a workaround in the form of an MSI transform, which is available from http://www.cisco.com/pcgi-bin/tablebuild.pl/windows?psrtdcat20e2 ( registered customers only) (file name vpnclient-international-transform-5.0.01.0600.zip). Future versions of the Cisco VPN Client for Windows will not require this workaround.

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 .

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/en/US/docs/general/warranty/English/EU1KEN_.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 Using Third-Party Support Organizations

Customers Without Service Contracts

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.

The regression in the fix for the" Local Privilege Escalation Through Default cvpnd.exe File Permissions" vulnerability (CSCtn50645) was found and reported to Cisco by Gavin Jones of NGS Secure. Cisco would like to thank Gavin Jones and NGS Secure for reporting this vulnerability and for working with us towards a coordinated disclosure of the vulnerability.

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.

This advisory is posted on Cisco's worldwide website at:

http://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20070815-vpnclient

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.

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.