RE: Windows Remote Desktop

From: Shawn Jackson (sjackson_at_horizonusa.com)
Date: 01/15/04

  • Next message: Shawn Jackson: "RE: Please help with this strangeness"
    Date: Thu, 15 Jan 2004 13:50:38 -0800
    To: "Depp, Dennis M." <deppdm@ornl.gov>, <jamesworld@intelligencia.com>
    
    

            Well if you use that example everything is subject to a MiM
    attack. You could do that with websites, application servers, network
    programs, etc. With Citrix you can setup a HTTP gateway, protect it with
    SSL/HTTPS then use the Citrix ICA encryption on top of that, only give
    the Cert to client you wish to have access to the gateway. That is how
    Citrix can be more secure then RDP. If you are not using a separate
    system for your http gateway you mitigate the risk of a MiM attack.
    Additionally you can create ICA Client packages that have all the
    required information hard coded, this makes it hard for the user to
    change the server information and harder for it to connect to a 'wrong'
    server. The TSAC (Terminal Services Advanced Client) has a web TS
    interface; you can protect that the same way using SSL and certificates
    and only allow known people to access it. I've personally never used
    TSAC in this way, but I believe it's possible.

            The older NT 4 Terminal Service edition used Citrix ICA
    protocols. RDP5 is a Microsoft only protocol and was created mostly from
    scratch. A good comparison of the protocols is at
    http://www.purenetworking.net/RDPvsICA.htm.

            Everything is possible in the world of security; you can't
    protect yourself 100% no matter how hard you try. The only thing we as
    security processionals can do is try and decrease/mitigate the risk as
    much as possible. I agree that use of RDP/ICA can open up a hole into
    your network. But you can mitigate the risk of a RDP/ICA connection with
    planning, thoroughness and foresight.

    Shawn Jackson
    Systems Administrator
    Horizon USA
    1190 Trademark Dr #107
    Reno NV 89521

    www.horizonusa.com
    Email: sjackson@horizonusa.com
    Phone: (775) 858-2338
                 (800) 325-1199 x338

    -----Original Message-----
    From: Depp, Dennis M. [mailto:deppdm@ornl.gov]
    Sent: Thursday, January 15, 2004 1:14 PM
    To: Shawn Jackson; jamesworld@intelligencia.com
    Cc: Michael Gale; security-basics@securityfocus.com
    Subject: RE: Windows Remote Desktop

    Shawn,

    I still fail to see the difference between Citrix and RDP as far as
    security goes. RDP like Citrix can be configured on the server side.
    As for the MiM attack. Theoretically I can setup an machine and have it
    masquerade as your Citrix server. When you logon to my machine you
    enter your Username and Password. I pass this information on to your
    Citrix server and I have compromised your data. This is possible
    because no authentication is done at the client to ensure your machine
    is authentic. This is true for both the HTTP interface/gateway and the
    ICA client. The same also holds true for the RDP protocol. (Which I
    believe has a lot of Citrix components in it.)

    I still don't want end users accessing their home workstation via RDP,
    Citrix, PCAnywhere, VNC or any other protocol. This creates another
    portal into my network for virii and worms.

    Denny

    -----Original Message-----
    From: Shawn Jackson [mailto:sjackson@horizonusa.com]
    Sent: Thursday, January 15, 2004 3:52 PM
    To: Depp, Dennis M.; jamesworld@intelligencia.com
    Cc: Michael Gale; security-basics@securityfocus.com
    Subject: RE: Windows Remote Desktop

            Citrix ICA defaults to the setting on the server side, so if you
    configured your server with *some* security then a 'basic default' is
    not the case. Personally I separate raw data (Files, Databases, etc) and
    interactive 'streaming' data. Raw data is a file/component in transit on
    the wire that can be sniffed and recompiled, while streaming data can't
    be recompiled into anything but can be sifted through for information.

            Capturing interface information from even an unencrypted RDP
    connection is difficult. Setup three workstations on a hub then setup
    VNC server on 1 and the viewer on the 2nd. From the 3rd workstation use
    SNORT and sniff the traffic between the two. Have another person play
    with the viewer to give you something too look at.

            To my understanding Citrix is only at risk of a MiM attack when
    using the HTTP interface/gateway and not the ICA client. If I'm
    incorrect please supply a link to information about this attack. Also I
    don't believe you can use SSL with XP RDP and that's Terminal Services.

            Personally I can justify the need of using RDP to my workstation
    at home, but then again I know that system and its security. I setup and
    maintain that network and servers so I can be reasonably sure that my
    connection is clean and my systems are not at risk. Would I personally
    let my users have RDP access to their workstations at home, nope. My
    reasoning for this is that they could be violating the company policy
    (browsing bad sites, playing games, listening to their MP3 collection,
    etc) and we can't see it. Would I let our IT/IS guys, yep. I'm not
    worried about people taking data offsite because everyone has USB drives
    already. I'm also not *too* worried about virii or hackers; it's that it
    just walks too fine a line with our security policy. But then again, if
    them have a business need...

            My 2,000,000 cents! :-)

    Shawn Jackson
    Systems Administrator
    Horizon USA
    1190 Trademark Dr #107
    Reno NV 89521

    www.horizonusa.com
    Email: sjackson@horizonusa.com
    Phone: (775) 858-2338
                 (800) 325-1199 x338

    -----Original Message-----
    From: Depp, Dennis M. [mailto:deppdm@ornl.gov]
    Sent: Thursday, January 15, 2004 10:29 AM
    To: Shawn Jackson; jamesworld@intelligencia.com
    Cc: Michael Gale; security-basics@securityfocus.com
    Subject: RE: Windows Remote Desktop

    Two statements I don't agree with:

    1) "Additionally no actual 'data' is transferred through the RDP
    connection, it's just interface information (mouse movement, button
    clicks, typing) and screen refreshes. Now if you were using the resource
    mapping then data would traverse the RDP connection and would be subject
    to its encryption."
            Data is sent over the wire concerning keystrokes, mouse
    movements and screen refresh data. Obviously this information,
    particularly keystrokes can provide data to a hacker. However all
    information set via RDP is encrypted the default is 56-bit with the
    capacity to use 128-bit RC4. Even when using local resources, the data
    is still encrypted with 128-bit security.

    2) "All in all I think that PCAnywhere and Citrix have
    more secure RDP/VNC like interfaces"
            The default security setting in Citrix is basic (no encryption)
    PCAnywhere maybe better, I'm not sure. Both Citrix and RDP are
    vulnerable to MiM attacks. Citrix does have the capability to use SSL
    but this is comprable to Microsoft's VPN solution.

    Denny

    -----Original Message-----
    From: Shawn Jackson [mailto:sjackson@horizonusa.com]
    Sent: Wednesday, January 14, 2004 6:36 PM
    To: jamesworld@intelligencia.com
    Cc: Michael Gale; security-basics@securityfocus.com
    Subject: RE: Windows Remote Desktop

            Well transferring data outside a company is easier then pie
    these days. With everything from encrypted email to USB drives it's hard
    to use that as a sole point 'ban' RDP to offsite resources. Unless
    you're running at high level security i.e. Military, Extremely Sensitive
    Work, National Security the movement of data offsite would be a
    secondary concern.

            The RDP encryption is 'in transit' protection and won't protect
    the resources. I personally never use the clipboard sharing,
    drive/printer mapping, etc. Access to those resources should be dictated
    by the company security policy and doesn't follow the 'security' of the
    protocol/connection. Seaming the connection is one-way (From Workstation
    or RDP Host) it hard to open a hole/exploit through an infected RDP host
    and use the RDP interface to your advantage.

            Additionally no actual 'data' is transferred through the RDP
    connection, it's just interface information (mouse movement, button
    clicks, typing) and screen refreshes. Now if you were using the resource
    mapping then data would traverse the RDP connection and would be subject
    to its encryption. All in all I think that PCAnywhere and Citrix have
    more secure RDP/VNC like interfaces but RDP is pretty secure by itself.
    Just as James stated, watch the local resource mapping.

    Shawn Jackson
    Systems Administrator
    Horizon USA
    1190 Trademark Dr #107
    Reno NV 89521

    www.horizonusa.com
    Email: sjackson@horizonusa.com
    Phone: (775) 858-2338
                 (800) 325-1199 x338

    -----Original Message-----
    From: jamesworld@intelligencia.com [mailto:jamesworld@intelligencia.com]

    Sent: Wednesday, January 14, 2004 3:03 PM
    To: Shawn Jackson
    Cc: Michael Gale; security-basics@securityfocus.com
    Subject: RE: Windows Remote Desktop

    Ahh,,

    but what about the option to connect local resources......

    Drives
    Printers
    Serial Ports
    Smart Cards

    ....

    Talk about the ability to transfer company data out... What is
    protecting
    the actual data, MS RDP encryption which defaults to "medium" security
    by
    default.

    Again it comes back to.......What is the company policy? If it doesn't
    cover it, the policy needs to be updated.

    -James

    At 12:14 01/14/2004, Shawn Jackson wrote:

    > Eh' for 'Testing' I use a remote SSH server off my backbone. I
    >do 'periodically' login to my remote XP workstation and do some work.
    >Because only screen information is transmitted even if that system was
    >hacked or infected with a virus it won't affect my network at work. My
    >XP system doesn't sit directly on the Internet through; it goes through
    >a Debian box running iptables.
    >
    >Shawn Jackson
    >Systems Administrator
    >Horizon USA
    >1190 Trademark Dr #107
    >Reno NV 89521
    >www.horizonusa.com
    >
    >Email: sjackson@horizonusa.com
    >Phone: (775) 858-2338
    > (800) 325-1199 x338
    >
    >-----Original Message-----
    >From: Michael Gale [mailto:michael@bluesuperman.com]
    >Sent: Tuesday, January 13, 2004 8:35 PM
    >To: security-basics@securityfocus.com
    >Subject: Windows Remote Desktop
    >
    >Hello,
    >
    > I have a question, I have locked down a company network
    allowing
    >only
    >web browsing, SSH and FTP. Nothing else is need and soon SSH and FTP
    >will be gone hopefully once the VPN is final.
    >
    >Right now a internal user is complaining about the fact their remote
    >desktop connection to their home PC is no longer working.
    >
    >The justification is that a remote PC out side the network is needed
    for
    >testing. At which point I gladly offered to setup a out side box for
    >testing. :)
    >
    >Any ways the question I have is, do you feel that Remote Desktop (into
    >WinXP) is a secure enough connection to allow it. I mind you that this
    >is supposed to be a outbound connection only but you never know with
    >windows.
    >
    >
    >--
    >Hand over the Slackware CD's and back AWAY from the computer, your geek
    >rights have been revoked !!!
    >
    >Michael Gale
    >Slackware user :)
    >Bluesuperman.com
    >
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  • Next message: Shawn Jackson: "RE: Please help with this strangeness"

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