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 https://sec.cloudapps.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

• 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 affected	Cisco Bug ID
  1. Local Privilege Escalation Through Microsoft Windows Dial-Up Networking Interface	All versions up to but not including 4.8.02.0010	CSCse89550 ( registered customers only)
  2. Local Privilege Escalation Through Default cvpnd.exe File Permissions	32-bit Cisco VPN Client: all versions up to but not including 5.0.01.0600	CSCsj00785 ( registered customers only)
  	64-bit Cisco VPN Client: 5.0.7.0240 and 5.0.7.0290	CSCtn50645 ( registered customers only) |(regression of fix for CSCsj00785 ( registered customers 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 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 https://sec.cloudapps.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) .

  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

  https://sec.cloudapps.cisco.com/security/center/cvssCalculator.x

  1. Local Privilege Escalation Through Microsoft Windows Dial-Up Networking Interface (CSCse89550 ( registered customers only) ) Calculate the environmental score of CSCse89550
  CVSS Base Score - 6.8
  Access Vector	Access Complexity	Authentication	Confidentiality Impact	Integrity Impact	Availability Impact
  Local	Low	Single	Complete	Complete	Complete
  CVSS Temporal Score - 5.9
  Exploitability		Remediation Level		Report Confidence
  High		Official-Fix		Confirmed

  2. Local Privilege Escalation Through Default cvpnd.exe File Permissions (CSCsj00785 ( registered customers only) and CSCtn50645 ( registered customers only) ) Calculate the environmental score of CSCsj00785 and CSCtn50645
  CVSS Base Score - 6.8
  Access Vector	Access Complexity	Authentication	Confidentiality Impact	Integrity Impact	Availability Impact
  Local	Low	Single	Complete	Complete	Complete
  CVSS Temporal Score - 5.9
  Exploitability		Remediation Level		Report Confidence
  High		Official-Fix		Confirmed