Cisco Systems VPN Client allows local logon with Elevated Privileges

From: Nick Staff (Nick.Staff_at_FOX.COM)
Date: 05/14/03

  • Next message: Henk van de Kamer: "Windows XP activation"
    Date:         Wed, 14 May 2003 10:09:15 -0700
    To: NTBUGTRAQ@LISTSERV.NTBUGTRAQ.COM
    
    

    Note: This is similar to the exploit where it's possible to log on to a
    Windows machine as local system by making a copy of cmd.exe and naming
    it logon.scr.

    The Cisco VPN client can be configured to start before the Windows log
    on in case a user needs to make a VPN connection before logging onto
    their domain. To that same effect the Cisco VPN client can also be
    configured to load a 3rd party application, like a dialer, to connect to
    an ISP. By default these settings are not locked to standard users
    because the configuration file responsible for holding these settings
    (vpnclient.ini) is installed to a non-restricted path
    (systemdrive%\program files\CiscoVPN).

    To log onto their workstation as the local system a standard user would
    simply need to configure their Cisco client to start up before windows
    log on and launch explorer.exe - this would bring them to the desktop
    where they could then do anything the local system could (add themselves
    to the local admins group, change file permissions, etc).

    Steps to Reproduce:

    - Install any 3.x version of the Cisco Systems VPN Client (could be
    other versions, but I've only tested using 3.x)
    - Open the VPN Dialer.
    - Select Options > Windows log on properties
    - Make sure all three boxes are selected (you must select the first box
    before the second box becomes active)
    - Click OK and then go to Options > Properties
    - Click on the connections tab and check the box next to 'Connect to the
    Internet via dial-up'
    - Select the radio button next to 3rd party dial-up application and
    enter the full path and file name of explorer.exe (i.e.
    c:\winnt\explorer.exe)
    - Click OK, Close, and then log out

    Note - if your desktop doesn't appear right away and instead you just
    get a 'welcome to windows' or 'configure you server' window, then close
    them, press ctrl-alt-del, and click connect when the Cisco client opens
    - then you will get the full desktop.

    Workarounds:

    Edit the ginadll value located in the registry key
    HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows
    NT\CurrentVersion\Winlogon. Change the valuedata back to msgina.dll
    (Cisco client changes it to csgina.dll).

    or

    Set the security on the vpnclient.ini file to deny write permission for
    standard users (note this will prevent them from being able to import
    additional connection entries or configure any options from within the
    client).

    Thanks,

    Nick Staff

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  • Next message: Henk van de Kamer: "Windows XP activation"

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