Local privilege escalation vulnerability in Cisco VPN client

2007.08.19
Credit: ngssoftware
Risk: High
Local: Yes
Remote: No
CWE: CWE-Other


CVSS Base Score: 6.8/10
Impact Subscore: 10/10
Exploitability Subscore: 3.1/10
Exploit range: Local
Attack complexity: Low
Authentication: Single time
Confidentiality impact: Complete
Integrity impact: Complete
Availability impact: Complete

======= Summary ======= Name: Permissively-ACLed cvpnd.exe allows interactive users to run arbitrary binaries with Local System Privileges Release Date: 16 August 2007 Reference: NGS00503 Discover: Dominic Beecher <dominic (at) ngssoftware (dot) com [email concealed]> Vendor: Cisco Vendor Reference: cisco-sa-20070815-vpnclient Systems Affected: All versions up to but not including 5.0.01.0600 Risk: High Status: Published ======== TimeLine ======== Discovered: 18 May 2007 Released: 22 May 2007 Approved: 11 June 2007 Reported: 23 May 2007 Fixed: 15 August 2007 Published: 16 August 2007 =========== Description =========== Impact: locally logged-on users of affected hosts can cause arbitrary binaries to be executed in the context of Local System. This effectively compromises the host. ================= Technical Details ================= Cisco's VPN client for Windows installs a Windows service, the "Cisco Systems, Inc. VPN Service" or CVPND, whose associated binary is C:\Program Files\Cisco Systems\VPN Client\cvpnd.exe. By default, the CVPND service runs as Local System. SERVICE_NAME: CVPND TYPE : 110 WIN32_OWN_PROCESS (interactive) START_TYPE : 2 AUTO_START ERROR_CONTROL : 0 IGNORE BINARY_PATH_NAME : "C:\Program Files\Cisco Systems\VPN Client\cvpnd.exe" LOAD_ORDER_GROUP : TAG : 0 DISPLAY_NAME : Cisco Systems, Inc. VPN Service DEPENDENCIES : TCPIP SERVICE_START_NAME : LocalSystem Interactive Users (i.e. those who have logged on locally) are granted Modify permissions to cvpnd.exe (and its parent directory), denoted by NT AUTHORITY\INTERACTIVE:C in the cacls output below. C:\Program Files\Cisco Systems\VPN Client\cvpnd.exe NT AUTHORITY\INTERACTIVE:C BUILTIN\Users:R BUILTIN\Power Users:C BUILTIN\Administrators:F NT AUTHORITY\SYSTEM:F BUILTIN\Administrators:F This allows normal users who have logged on to a susceptible host to move cvpnd.exe to another location, and substitute another binary for cvpnd.exe. When the CVPND service restarts (e.g. on reboot), the replaced cvpnd.exe will run in the context of Local System. This effectively escalates users' privileges, thereby compromising the host. =============== Fix Information =============== Upgrade to a fixed version of the Cisco VPN client: see Cisco's advisory at the URL below for more details. http://www.cisco.com/warp/public/707/cisco-sa-20070815-vpnclient.shtml Alternatively, as a workaround, revoke access rights for NT AUTHORITY\INTERACTIVE from cvpnd.exe, e.g.: C:\Program Files\Cisco Systems\VPN Client>cacls cvpnd.exe /E /R "NT AUTHORITY\INTERACTIVE" -- NGSSoftware Insight Security Research


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