Random thoughts on wifi and vpn.
Posted Tue, 29 Aug 2006
Food for thought: My home vpn is a very simple poptop setup. It does not use certificates. How do I verify that my vpn connection is untainted? How difficult would it be to intercept my vpn connection request with a rogue vpn?
Let's say I'm on Google's free wifi here in Mountain View, and someone's being naughty by putting up the following rogue services: dhcp, dns, and vpn. It is trivial to advertise a route on the network and redirect vpn connections to a rogue vpn service. This vpn service could use the intended vpn as an authentication service. In doing so, the "bad guy" can quite easily join the two vpn tunnels such that the victim has no idea he has been victimized.
Put simply, how hard would it be for me, personally, to do this? Tools that come to mind, are: FreeRadius, Poptop server, isc-dhcp server, BIND 9, pf. Tack on a trivial script to interrupt the normal network services such as DHCP and DNS, and you've got something that can easily be deployed on a laptop.
I'm sure there are technologies to prevent this kind of MITM attack on vpns, right? IPSec, perhaps? I don't know. More research is required.
How secure are you on your favorite wifi hotspot? How secure are the "secure" services we rely on?