First Hamster, now Firesheep: A researcher has now made it possible for the average Joe to hijack a WiFi user's Facebook, Twitter, or other unsecured account session while sipping a cup of Joe at the local coffee shop.

The new tool for "sidejacking," or hijacking someone's HTML session cookies, is a Firefox extension called Firesheep, which was released over the weekend in conjunction with the Toorcon hacker conference. Firesheep was developed by Eric Butler, a Seattle-based Web application software developer and researcher.

Sidejacking attacks are nothing new--WiFi is notoriously risky, and most websites aren't SSL-encrypted today, leaving users open to having their sessions sniffed and hijacked when they log onto sites such as Facebook from the WiFi at Starbucks. Firesheep basically makes this type of attack easy enough for any nontechnical person to do: The tool pops up a window, you click the "Start Capturing" button, and it finds and displays user accounts currently on insecure websites via the WiFi network.

"Their name and photo will be displayed: Double-click on someone, and you're instantly logged in as them," Butler explains in his blog post about Firesheep.

The tool has been downloaded more than 129,000 times thus far, according to Butler.

Robert Graham, CEO at Errata Security, who developed and released his Hamster sidejacking tool three years ago, says although sidejacking has been a well-known threat for 10 years, Firesheep makes the attack more visual and easy to execute. "The way I did it with [my tool], I had to guess where the cookies were going," Graham says, adding that Firesheep grabs that information via the browser and more quickly. "[Butler's] tool works in cases where mine doesn't. It's a better solution."

Firesheep takes advantage of websites that don't SSL-encrypt logins, so when a user visits Facebook, Twitter, Hotmail, or YahooMail, his cookies can be automatically lifted and used by an attacker on the WiFi network to take over his account.

"This made it insanely easy and visible," says Beth Jones, a security expert with Sophos. "Everyone has been able to hack into cookies forever. But it's never been so easy, and [with] graphics."

The underlying problem, of course, is that most websites are not SSL-secured. Even Twitter's SSL site is an option and not the default version. Aside from using a VPN connection or a proxy--neither of which would be practical for many consumers--you can download another Firefox add-on called Force-TLS. which automatically directs you to the SSL version of a site if one exists.

Butler, meanwhile, says he hopes Firesheep will force websites to go SSL. "Websites have a responsibility to protect the people who depend on their services. They've been ignoring this responsibility for too long, and it's time for everyone to demand a more secure Web. My hope is that Firesheep will help the users win," he said in his blog post.

Errata's Graham says he'd like to be able to say that sidejacking is old news. "I should be able to say that," he says. "But I can't because I can take this down to Starbucks and hack people, and get to their email and their bank account. That should not work."

Firesheep is free and currently available now for Mac OS X and Windows; it will later run on Linux as well.

"People have been living under the impression that capturing a session by stealing a cookie can only be done by skilled hackers with special tools," blogged Mikko Hypponen, chief research officer for F-Secure. "This has now changed."

Have a comment on this story? Please click "Discuss" below. If you'd like to contact Dark Reading's editors directly, send us a message.