Summary

• Cisco Secure Desktop (CSD) software is affected by three vulnerabilities that may:

  • Cause information produced and accessed during an Internet browsing session to be left behind on a computer after an SSL VPN session terminates.
    
  • Allow users to evade the system policy that prevents them from leaving the Secure Desktop while a VPN connection is active.
    
  • Allow local users to elevate their privileges.
    

  Cisco has made free software available to address these vulnerabilities for affected customers. There are workarounds available to mitigate the effects of some of these vulnerabilities.

  This advisory is posted at https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20061108-csd.

Affected Products

• This section provides details on affected products.

  Vulnerable Products

  The vulnerabilities described in this document exist in versions 3.1.1.33 and earlier of Cisco Secure Desktop.

  Products Confirmed Not Vulnerable

  Versions 3.1.1.45 and later of the Cisco Secure Desktop are not affected by these vulnerabilities.

  No other Cisco products are currently known to be affected by these vulnerabilities.

Details

• The Cisco Secure Desktop (CSD) seeks to minimize data from being left behind after an SSL VPN session terminates. In particular, CSD works to reduce, via encryption, the risk that cookies, browser history, temporary files, and downloaded content remain on a system after a remote user logs out or an SSL VPN session times out.

  CSD is affected by the following vulnerabilities:

  Information Leakage via Spawned Browser

  This vulnerability occurs when the Internet browser that is automatically spawned to display a home page after an SSL VPN session is established uses a directory outside of the vault maintained by CSD to store its session information, i.e. browser cache (also known as "temporary Internet files"), history, cookies, etc. This also allows users to save files downloaded during this Internet browsing session to outside of the CSD vault, which would result in unencrypted files remaining in the system after the SSL VPN connection terminates.

  Please note that this vulnerability only occurs when the Cisco SSL VPN Client is configured to spawn a home page after a successful connection. Spawning a home page after a successful connection is a configuration option of the VPN headend; that is, it is not a Cisco Secure Desktop configuration option and is not enabled by default.

  This vulnerability is documented by Cisco Bug ID CSCsg05935 ( registered customers only) — SVC's spawned browser saves to nonsecure desktop.

  System Policy Evasion

  This vulnerability allows users to switch between the Secure Desktop and the Local (nonsecure) Desktop when using certain applications that attempt to switch to the default desktop. This can occur even when the system administrator has configured CSD to prevent switching between the Secure Desktop and the Local Desktop.

  This vulnerability is documented by Cisco Bug ID CSCsg11636 ( registered customers only) — Applications that switch to the default desktop cause CSD to minimize.

  Local Privilege Escalation

  The default permissions of the directory where CSD is installed, and its parent directory, allow any user to modify the contents of a CSD installation, including renaming, deleting and overwriting files. Unprivileged users can make use of this to elevate their privilege and obtain LocalSystem-equivalent privileges by replacing certain CSD executables that are run as system services and with LocalSystem privileges.

  CSD is installed by default into the directory %SystemDrive%\Program Files\Cisco Systems\Secure Desktop\.

  Note:  %SystemDrive% is a Microsoft Windows environment variable that holds the drive that Windows was installed to. Normally, Windows is installed in the first hard disk and therefore %SystemDrive% is usually C:.

  Please note that there are other Cisco products that install their files in a directory under %SystemDrive%\Program Files\Cisco Systems\. When these products are installed they normally inherit the permissions from the parent directory (%SystemDrive%\Program Files\Cisco Systems\). Therefore, as a side effect of this vulnerability in CSD, other products may be affected if they are installed after a vulnerable version of CSD is installed.

  This vulnerability is documented by Cisco Bug ID CSCsg29650 ( registered customers only) — Insecure file and directory permissions in CSD installation.

  For information about local system level privileges, please refer to:

  • LocalSystem Account
    http://msdn.microsoft.com/library/default.asp?url=/library/en-us/dllproc/base/localsystem_account.asp
    

Workarounds

• This section describes workarounds for these vulnerabilities.

  Information Leakage via Spawned Browser

  A workaround for this vulnerability is to disable the spawning of a home page after a successful VPN connection. This setting is disabled by default and is a VPN headend configuration setting, not a Cisco Secure Desktop configuration setting.

  To disable the spawning of a home page after a successful VPN connection on the Cisco VPN 3000 Series Concentrators, log into the web administration interface of the concentrator via the URL:

  https://<IP address of concentrator>/admin/

  and then clear the Homepage URL under "Configuration | User Management | Groups | Modify {groupname}"

  For more information on setting a home page for the Cisco VPN 3000 Series Concentrators, visit the following URL:

  http://www.cisco.com/en/US/products/hw/vpndevc/ps2284/products_configuration_guide_chapter09186a00803ee1f0.html#wp2267654

  To disable the spawning of a home page on the PIX and ASA security appliances, modify the "homepage" attribute under WebVPN Group Policy and User Attributes.

  For more information on setting a home page for the Cisco PIX and ASA security appliances, visit the following URL:

  http://www.cisco.com/en/US/products/ps6120/products_configuration_guide_chapter09186a008063b194.html#wp1040653

  System Policy Evasion

  There are no workarounds for this vulnerability.

  Local Privilege Escalation

  A workaround for this vulnerability is to change the permissions of the directory where CSD is installed, and all files under it, so only users with administrative privileges can modify the contents of the CSD installation. CSD is installed by default into the directory %SystemDrive%\Program Files\Cisco Systems\Secure Desktop\.

  The actual permissions that need to be set can be inherited from the directory %SystemDrive%\Program Files\, which by default, have secure permissions.

  Changing directory permissions can be accomplished using the Windows Explorer or using the CACLS.EXE command-line utility distributed with modern versions of the Microsoft Windows operating system.

  As mentioned in the Details section, if another Cisco product that installs its files to its own directory under %SystemDrive%\Program Files\Cisco Systems\ is installed after a vulnerable version of CSD is installed, that other product may become affected as a side effect of the CSD vulnerability. Therefore, it is recommended to also fix permissions of directory and files of other Cisco products that have been installed after the installation of a vulnerable CSD version.

  Please note that uninstalling CSD will remove the %SystemDrive%\Program Files\Cisco Systems\Secure Desktop\ directory, but will not remove nor change the permissions of the parent directory, i.e. %SystemDrive%\Program Files\Cisco Systems\.

Fixed Software

• The vulnerabilities described in this document are fixed in version 3.1.1.45 of the Cisco Secure Desktop software.

  Cisco Secure Desktop software can be downloaded from the following location:

  http://www.cisco.com/pcgi-bin/tablebuild.pl/securedesktop?psrtdcat20e2 ( registered customers only)

  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.

Exploitation and Public Announcements

• The Cisco PSIRT is not aware of any public announcements or malicious use of the vulnerabilities and limitations described in this advisory.

  The "Information Leakage Via Spawned Browser" and the "System Policy Evasion" vulnerabilities were reported to Cisco by customers.

  The "Local Privilege Escalation" vulnerability was reported to Cisco by iDefense. iDefense's advisory is available at http://labs.idefense.com/intelligence/vulnerabilities/display.php?id=442 .

  Cisco would like to thank them for working with us towards coordinated disclosure of these vulnerabilities.

URL

• https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20061108-csd

Revision History

• Revision 1.2	2007-February-21	Clarified workaround for the "Information Leakage via Spawned Browser" vulnerability (CSCsg05935).
  Revision 1.1	2006-November-08	Included link to iDefense advisory.
  Revision 1.0	2006-November-08	Initial public release.

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