Hacking WiFi

The dream of ubiquitous, free WiFi networking has been taunting us from just over the horizon ever since the first access points appeared in public. So far, it's still a dream.

Rather than enabling a utopian world of free, anywhere, anytime bandwidth, the practical realities of the WiFi market have crushed our dreams and left us in a morass of incompatible, for-fee, by-the-hour services. Even in the Red Carpet Club airline lounge – for which I dutifully pay $500 each year – I still have to pay extra if I want to check my email – and I can only do it through T-Mobile, the airline's preferred partner, of course.

Last month's announcement that AT&T will replace T-Mobile in Starbucks – perhaps the most popular WiFi hot spot in the market – could start a new era in wireless connectivity. According to the announcement, the service will be free for Starbucks patrons, which comprises the entire population of the world and a few lower life-forms.

Yes, you'll have to buy a Starbucks card, but there's no additional cost to use the wireless network. Until the cellphone companies include free data for our laptops, WiFi hotspots will continue to be the connectivity of choice for any casual traveler with a laptop.

Which is really good news for the bad guys.

I'm far from anti-WiFi, but let's face it: It's trivial to exploit the flaws in WiFi security. While the latest wireless encryption, WPA2, is rock solid when deployed properly, most WiFi hotspots offer absolutely no encryption or other security for clients. You're open to everything from sniffing to sidejacking to man-in-the-middle (MITM) attacks. My personal favorite is an MITM attack called the "Evil Twin" that's not only easy to execute, but fun to build.

The basic principle of an Evil Twin exploit is that you create your own wireless hotspot using the same name as the official one in the same location. You then trick clients into connecting to you instead of the real access point. By hijacking the connection, you can sniff traffic, redirect requests, insert your own traffic, and directly attack the client.

The most common way to execute the attack involves using a laptop with a couple of wireless cards, but I prefer to supersize things. I start with a hackable wireless access point, like a Linksys WRT54GL, a laptop with a broadband cellular wireless connection, a power-boosted WiFi antenna, a car battery jump starter, and a power inverter.

I've replaced the firmware on the access point with DD-WRT, a free download that replaces the manufacturer's firmware and allows you to run your own software on the device (you can also use OpenWRT). I boost the power of my access point and enable a feature called "NoCatSplash" so that anyone who connects to me sees my custom login page, which I've conveniently enhanced with a malicious image to exploit vulnerable systems.

The access point uses my laptop with the cellular card for Internet access, which also hosts my attack software (I use Core Impact, but Metasploit now supports this kind of attack). I power the access point off the car jump starter and stuff it all into a big, ridiculously heavy, laptop bag.

Once I'm ready, I just walk in to my target site, set the access point to the same network ID as the public WiFi, and use another laptop to start knocking people off the local network. Since my beast of an Evil Twin is more powerful than the local hardware, victims should reconnect through me. If they are vulnerable, I own them. If they aren't, I still control their connection, and I can sniff or change their network traffic.

This attack never fails to garner attention when I demonstrate it at conferences, and I'm working on a newer version, where I'll run Metasploit natively on the access point and reduce the need for the laptop. Then I could even hack the hardware into a lamp or other innocuous accessory that I could leave behind. Some hackers run the attack on handheld devices, but I like the extra power of access points.

So how can you protect yourself from this attack? I use a cellular connection or tunnel all of my public WiFi traffic through a hard-to-spoof virtual private network, especially on my iPhone. There isn't anything inherently wrong with free WiFi, but you definitely need to take precautions when using it in public.

— Rich Mogull is founder of Securosis LLC and a former security industry analyst for Gartner Inc. Special to Dark Reading.