Tools Gut Firesheep Cookie Hijacking Attack

How Firesheep Can Hijack Web Sessions

Scared by the recent arrival of Firesheep, a controversial plug-in for Firefox that allows attackers to hijack your web sessions? The cookie-stealing tool, downloaded at least 600,000 times to date, works against users of a number of Web 2.0 websites, including Facebook, Twitter, and Flickr.

Now, however, free tools are appearing to help users defend themselves.

On Monday, SaaS security firm Zscaler released BlackSheep, a free Firesheep countermeasure. (As with Firesheep, Windows users must first install Winpcap.) BlackSheep works by making HTTP requests using fake variables to the websites watched by Firesheep. BlackSheep then detects and blocks Firesheep clients at work on the local network when they attempt to reuse the fake variables.

Meanwhile, Gunnar Atli Sigurdsson, a 21-year-old engineering students at the University of Iceland, released FireShepherd for Windows, "a small console program that floods the nearby wireless network with packets designed to turn off Firesheep." The tool has the added benefit of blocking Firesheep for anyone else using the same Wi-Fi connection.

Another workaround is HTTPS Everywhere, from the Tor Project and Electronic Freedom Foundation, which forces websites to SSL-encrypt every page. The only caveat is that websites must offer HTTPS.

Countermeasures aside, controversy continues to rage over whether Firesheep itself is good or bad. The goal of releasing it, according to its creator, Eric Butler, was to expose the lack of security inherent to using unencrypted Wi-Fi networks.

"Facebook is constantly rolling out new 'privacy' features in an endless attempt to quell the screams of unhappy users, but what's the point when someone can just take over an account entirely?" said Butler. Indeed, the necessary packet-sniffing tools, including free utilities such as NetStumbler and Kismet, have been available for years -- and Firesheep blockers won't even detect them.

Accordingly is it "mission accomplished" for publicizing Wi-Fi insecurity? "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. This has now changed," said F-Secure's chief research officer, Mikko Hypponen.

"What can users do right now? Force SSL on if you can. Don't use Wi-Fis without encryption. Or, use a VPN," said Hypponen. "If you have a VPN, always turn it on when you are on a hotspot, even if you're not 'working' but just surfing Facebook. All good VPN products will encrypt all of the traffic, even to Facebook."

Why not simply SSL-enable for Facebook, Twitter, and everything else under the sun? Many sites do use SSL, but only for encrypting logon information. With the exception of Gmail, few use SSL for the entire session.

Previously, using SSL took a bite out of performance. But today, said Google software engineer Adam Langley, "SSL/TLS is not computationally expensive anymore." In other words, "you too can afford to enable HTTPS for your users."

According to statements made by Facebook and Twitter, they're working on it.