Security Basics mailing list archives
RE: VNC Security
From: "Joshua Berry" <jberry () PENSON COM>
Date: Tue, 19 Apr 2005 17:42:48 -0500
To the original poster: It is my *opinion* that using VNC should be avoided completely. The last time that I used VNC it only support a password, and no user name. This leaves only the password to brute-force, considerably lessening the time needed to break in. Also, you are making the assumption that everyone uses plain text POP, I only use POP over SSL, IMAP over SSL or HTTPS to access my email. Also, this is not a good example because POP user accounts/passwords only give you someone's email, a VNC password will give you full access to the server/desktop it is running on. The passwords can be sniffed on your local network or they can be sniffed on the network that the server/desktop you are connecting to resides on. If this is a critical box, then now anyone that can sniff the network can also gain a login to this box to do whatever they want. I believe that VNC includes SSL or some other decent means of encryption now. To the first follow up poster: a. Somebody just needs to get the password in that 20 minute interchange, which is not too hard if they are only sniffing for X sessions. They can just dump that to a file and leave it running until it picks something up. Also, you can setup something to probe the box on that port, so the next time VNC is enabled they can login. I am curious how you would notice someone sniffing the network? I only see this as being possible if the host was running linux/unix and forwarding their syslogs to you, so that you could see when a NIC entered promiscuous mode. Lastly: I have seen several VNC exploits available over the years, so this is just a whole new service that you are exposing to risk that you often don't need to (because if it is Linux you have SSH, and if it is a windows box you have Terminal Services) -----Original Message----- From: Andy Bruce - softwareAB [mailto:andy () softwareab net] Sent: Tuesday, April 19, 2005 7:55 AM To: Steve Bostedor Cc: security-basics () securityfocus com; vnc-list () realvnc com Subject: Re: VNC Security This is a very interesting question to me. In my own case, I do have SSH setup thru Cygwin (http://www.cygwin.com/) for my local network and I use VNC thru that connection when I need to manage my own stuff remotely. However, I have to admit that when I use VNC to aid remote clients (which happens quite frequently) I don't worry about encryption whatsoever. FWIW, here's my approach: 1. I don't even try to explain setting up an SSH daemon to them. I simply have them install the VNC server in user-mode and start it. 2. If I can't explain to them in 5 min or less how to do port forwarding, I just have them connect directly to their cable/dsl modem. 3. Get the debugging and/or support done. 4. Have them stop the VNC server. Since it isn't running as a service, it won't start up next time and so won't be a security risk. 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. I have to agree with Steve that this is, for all practical purposes, a non-existent security risk. The only things that could go wrong: a. "Somebody" is sniffing the packet stream while the VNC passwords are being exchanged, and, during that 20 minute interchange, cracks the password and logs onto the VNC server. Of course, we would notice this problem on both ends! b. I have never captured the data shared between client and server (screen/UI deltas) and so have no idea if these pose a security risk or not. c. While the VNC server is running and they are connected to the internet (port forwarding has the same problem as direct connect) a port sniffer detects that 5900 is available and immediately zooms in thru some VNC security hole. Wez would know a lot more about this possibility than me, though! Am I missing something here? Steve Bostedor wrote:
I'd like to know if anyone has any working examples of why an unencrypted VNC session over the Internet is seen as such a horrible security risk. I understand that unencrypted ANYTHING over the
Internet
lends the chance for someone to decode the packets (assuming that they capture every one of them) but in reality, what are the real risks here and has anyone successfully captured a VNC session from more than 2 router hops away and actually gotten any meaningful information from
it?
I've captured a big chunk of a LOCAL session using Ethereal and the
only
thing that I can see that is usable is the password exchange. Agreed that this could be a problem if someone just happened to be sniffing your local LAN segment at that exact moment and happened to capture
your
encrypted VNC password, he could crack the password and log in himself. But how paranoid is it to go through all of the trouble of setting up SSH to avoid that when you could just change your VNC password often
and
make sure that your local LAN is reasonably secure from prying eyes? How about once it gets out on the Internet? Packets bounce all over
the
place on the Internet. What are the odds that someone out there will pick your VNC packets out of all of the millions of packets running through the back bone routers without being noticed, capture enough of them to possibly replay a session, and actually have the patience or
the
tools to do so. I've scoured the web out of this curiosity, looking
for
a tool to put VNC packets together into something useful for a hacker. There's nothing. Nada. So, I guess that what I'm asking is; what all of the fuss is about? Your POP3 password likely gets passed unencrypted but we're being asked to be paranoid about an encrypted VNC password? This is all coming
from
a discussion that I had with someone over the merits of using SSH with VNC over the internet for a 10 minute VNC session. Does anyone have anything that's not hypothetical? Is there a tool
that
I'm missing out there that does more than just crack a VNC password? Does anyone know of any reported security breaches where VNC was a weakness? _______________________________________________ VNC-List mailing list VNC-List () realvnc com To remove yourself from the list visit: http://www.realvnc.com/mailman/listinfo/vnc-list
Current thread:
- Re: VNC Security, (continued)
- Re: VNC Security Zachary Mutrux (Apr 20)
- Re: VNC Security Scott C. Best (Apr 27)
- Re: VNC Security Mike Miller (Apr 26)
- Re: VNC Security Andy Bruce - softwareAB (Apr 26)
- Re: VNC Security Mike Miller (Apr 26)
- Re: VNC Security Zachary Mutrux (Apr 20)
- Re: VNC Security Alexander Bolante (Apr 20)
- Re: VNC Security Times Enemy (Apr 20)
- Re: VNC Security Zachary Mutrux (Apr 20)
- Windows Remote Access Tools Sagiko (Apr 28)
- Re: Windows Remote Access Tools Adam Jones (Apr 29)
- RE: VNC Security Joshua Berry (Apr 20)
- RE: VNC Security Steve Bostedor (Apr 20)
- Re: VNC Security Alexander Bolante (Apr 20)
- RE: VNC Security Steve Bostedor (Apr 20)
- RE: VNC Security Steve Bostedor (Apr 20)
- RE: VNC Security Joshua Berry (Apr 20)
- RE: VNC Security Steve Bostedor (Apr 20)
- RE: VNC Security Joshua Berry (Apr 21)
- RE: VNC Security Joshua Berry (Apr 21)
- Re: VNC Security Alexandre Zglav (Apr 21)
- RE: VNC Security Conlan Adams (Apr 26)
(Thread continues...)