Re: VNC Security

From: Alexandre Zglav (azglav_at_heritage.ch)
Date: 04/21/05

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    To: "Bart Crijns <gorby" <gorby@skynet.be>
    Date: Thu, 21 Apr 2005 09:39:15 +0200
    
    

    Hi all,

    Aside from SSH tunneling, do you think that there would be a way to use
    regular SSL to encrypt the vnc stream between two computers ? Or maybe
    something more complicated such as RSA and securid autentication ? I
    thinking of this in the purpose of offering remote assistance services for
    a wide set of users. Such a practice would require me to sufficiently
    secure the stream between my help desk center and my users whilst I cannot
    afford to spend too much time explaining port forwarding and SSH etc ...

    Thanks

    ________________________________________________

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    Alexandre Zglav
    Heritage Bank & Trust
    12 cours des bastions
    P.O. Box 3341
    1211 Geneva
    Switzerland
    Phone : ++ 41 22 817 31 11
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    azglav@heritage.ch
    www.heritage.ch
    ________________________________________________

                                                                                                                                       
                          Bart Crijns
                          <gorby@skynet.be> To: Andy Bruce - softwareAB <andy@softwareab.net>
                                                   cc: Steve Bostedor <Steveb@tshore.com>, security-basics@securityfocus.com,
                          19.04.05 23:15 vnc-list@realvnc.com
                                                   Subject: Re: VNC Security
                                                                                                                                       

    Andy Bruce - softwareAB wrote:

    > 5. Tell them to turn off port forwarding from the router (if they
    > could grok it), or just have them connect their PC back to the router
    > and their router back to the cable/dsl modem. In either case, 5900
    > isn't available to the outside world so there's no risk even if they
    > were running VNC in service-mode.

    Another (very easy) way to make these connections more secure with those
    users is the following:
    I'm using UltraVNC, so I'm not certain that everything is possible in
    other VNC variants.
    - set a very long and very difficult password for the server (it will
    never be used anyway in this approach)
    - disable the 'accept socket connections' checkbox in the server
    properties (may be UltraVNC only)
    - when the users need assistance let them start the server, and instead
    of connecting to their PC, you start the viewer in listen mode
    - tell them your IP, and have them add a client throug the system tray
    icon's menu, and have them enter your IP when requested.
    You'll need to have your router setup for port forwarding to the ports
    for the listening viewer...

    That way noone needs to know their password, and with UltraVNC the
    server isn't even accepting connections in the unlikely event that the
    password is known by someone. No password is transmitted, and the only
    thing that could be captured is the data sent during the VNC session,
    which isn't too much of a problem in most cases when helping someone out.
    Furthermore, no incoming ports need to be opened on their router,
    because most users aren't really capable of changing that themselves.

    Of course, when connecting to my own PC via VNC, I use a SSH tunnel.

    > Am I missing something here?

    Other than the fact that in the unlikely event of someone malignant
    actually taking over their PC, you'll be the one who's blamed... no :-)
    I think the method I described is a bit safer, and also very easy to
    explain to the person at the other end of the line. If I may have missed
    something in my plan, please correct me.

    Kind Regards,
        Bart Crijns

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