Bugtraq: FON Router allows anonymous web access

[l.friedrichs () gbs nitag de]

Description:
"La Fonera" routers distributed by FON allow web access to unauthenticated users via DNS tunneling.

Explanation:
The router gives a client an DHCP answer but does not forward ip traffic until the client authenticates via the captive 
portal. The given DNS server address is the router itself so there is a DNS forwarder running on the router. Even an 
unauthorized client is allowed to surf certain sites as of obvious reasons (google, skype and the accesspoint's owner's 
site) but instead of filtering the dns requests for these few domains, it resolves all domains. This is where an DNS 
tunnel comes handy...

Environment:
Tested with router's standard config on 01/04/07. Runs smoothly with NSTX (http://nstx.dereference.de/nstx/ 
Version 1.1-beta6) and an ssh-session for connection testing without any authentication via the FON captive portal.

Impact:
Unauthorized ressource usage (internet bandwidth)

Solution:
New firmware from FON, workaround can be rate limiting DNS traffic on the real router (if possible...)