At work we mostly use Ubuntu for our Linux needs.
Recently our campus security officer started alarming a bunch of VNC services as having potentially been compromised by the RealVNC noauth exploit. Some of them I was morally positive were not vulnerable, so I decided I'd try out the metasploit 2.6 (latest stable at the time) bypass exploit from my trusty Ubuntu box. It didn't work, as expected, but I wanted to prove that it would work on vulnerable systems; such demonstrations carry a lot more weight. I have a VMWare Workstation for Linux license, so I made a new VM "PantsDown XP", installed XP SP2 to it, disabled updates, and disabled the firewall. I dug around and found a RealVNC 4.1 Windows executable - google is your friend - and installed it.
Then I RTFMed, fired up msfconsole, and exploited it. Or rather, I tried to. vncviewer would try to start, but nothing happened. I googled, I beat my head against it, I tried disabling the autolaunch of vncviewer and did it by hand, no joy. I made a Windows 98SE box, unpatched, and put the same VNC server on it. No luck. (At least the 98 box takes 1/4 the RAM.)
Finally, today, I fired up my Fedora Core 5 virtual machine whose only use to that moment had been to demonstrate how to sync such a machine against our local repositories, and installed metasploit 2.7 on it. (Couldn't find the perl packages for Readline that it really wants to use and I hate using CPAN and the like, so I lived without that.) Fired up msfconsole, and... poof. It worked against the 98 box.
I haven't tried it against the PantsDownXP box, but I'm sure it would work. Just now I fired up a Dapper Drake LiveCD (well, the install CD), enabled remote desktop, pointed metasploit at it, and started the install from the resulting VNC window. (In its defence, the Ubuntu box asked me if I wanted to let the Fedora box through.)
So, metasploit doesn't like Ubuntu very much, I guess, or at least not the realvnc exploit - I haven't tried any others. I'll see if I can figure out why, but figured I'd post this in case google finds it and anybody else has the same problems.