'BlackSheep' Sniffs Out Firesheep WiFi-Hacking

A researcher today released a Firefox plug-in that serves as an early warning system of sorts for WiFi users whose Web sessions are either at risk or have been already hijacked by someone running the Firesheep sidejacking tool.

The so-called BlackSheep tool is meant as a counter-punch to the new Firesheep plug-in for Firefox that makes it possible for anyone, technical or not, to easily hijack another user's HTML session cookies over a WiFi network. The Firesheep sidejacking tool, developed by Eric Butler, a Seattle-based Web application software developer and researcher, takes a new spin on an already known attack: it basically makes these types of attacks point-and-click.

The tool shows a "Start Capturing" button, which when clicked, shows names and photos of Facebook users on their accounts on the WiFi network at the coffee shop or hotel. Firesheep has attracted hundreds of thousands of downloads since Butler unleashed it during Toorcon last month.

Enter BlackSheep: its author Julien Sobrier, senior security researcher at Zscaler, says the tool is meant to alert WiFi users when someone is running Firesheep on the network. "If you used BlackSheep and were on WiFi, you could see a warning that someone on the same wireless network was using Firesheep. You would know someone is spying on you and trying to sniff your session, so you shouldn't go to Facebook," for example, Sobrier says. "It warns you to be careful."

It basically warns you to log off WiFi or risk getting hacked, or that your Facebook or other online account may already have been hacked.

There's no easy way to block Firesheep, he says. "The only way is to use encryption, which most websites are not designed for," he says. A virtual private network (VPN), which encrypts communications, is another way to protect yourself from sidejacking and other forms of WiFi sniffing.

But critics argue that because BlackSheep does nothing to actually prevent sidejacking, it doesn't really do much to protect users. "Its protection is poor," says Robert Graham, CEO of Errata and developer of sidejacking tool Hamster. "[And] there are numerous holes in the 'detection.' It would fail to detect my Hamster tool, for example, because Hamster does not make automated queries to fetch a user's picture like Firesheep does. It would also fail to detect hackers using two connections."

Graham says the Electronic Frontier Foundation's HTTPS-Anywhere tool does more to protect users at least for sites that offer SSL sessions. "The correct solution is encryption. Any company solving this problem without encryption is providing snake oil," Graham says.

Sidejacking, or hijacking a user's HTML session cookies, is a well-known attack vector and risk of using WiFi unprotected. SSL-based websites are safe as long as they are encrypted throughout the session. Many websites just use SSL for their login pages and then go unencrypted for the rest of the session.

BlackSheep works like this: it emits phony session ID information on the network and then watches to see if that session ID gets hijacked. Once Firesheep makes a request for that same domain, BlackSheep is clued in that Firesheep is there and active. It then alerts the user that Firesheep is on the network.

Zscaler says that Firesheep and BlackSheep can only run on the same machine if they are installed in separate Firefox profiles.

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