Re: Wired detection of rogue access points

Haven't we gone through this before?

For each of you that thinks they have a way to detect a wireless
access point using only the LAN, please demonstrate how you would
detect this.

A wireless router is hooked up to the network jack of a printer. The
wireless router is configured to use the printer's MAC address. The
wireless router is set up with the printer's new IP address as it's
DMZ host[1]. From the outside, all port scans and probes are going to
the printer.

There might be some IP stack differences, but you'd have to have a
very comprehensive database to figure that out, and the time to scan
at that level could prevent that level of probing on large networks.

From Mr. Waters, I expect no less than the results of an actual scan
on a live network with
this set up running on it. :)

Now that was easy. No real expertise required on the person who set up
the rogue access point, just a little cleverness. So lets say I want
to put the rogue access point on your network.

Same router, new firmware. My new OS is reconfigured a bit.

The WAN port bridges to LAN1. WAN plugged in to wall, LAN1 plugged in
to printer. All other ports and the wireless are configured for the
private LAN on the router.

My OS sniffs packets and determines the IP address in use by the
printer. Now it statefully NAT's packets from it's private network to
the printer's IP address. It filters return packets on the bridge so
that the printer doesn't see any of the traffic.

Now how do you find it over ethernet with scanning or probing? It
doesn't respond to anything. It doesn't interfere with the printer's
IP stack fingerprints when the printer is probed. Only watching the
unusual traffic coming from the printer or scanning for the RF would
pick this up.

Oh yeah, heaven forbid that I go all out and not use normal wireless
frequencies. Maybe pop in an EVDO card instead of an 802.11 one. Who
would want their own Internet accessible back door into your intranet
anyway?

OK, so my OS isn't completely off the shelf, and I haven't had the
time to sit down and make it work yet. The open source pieces are all
there, however, just waiting for the right person to come along and
duct tape them all together.

Bottom line: Ethernet cannot be completely secured. Either encrypt
everything, watch everything, or physically control access to
everything.

Regards,
Eric Hacker, CISSP

[1] I hate using the term DMZ for this use, but that's what is used on
all the router configurations.

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