There have been a number of reports about a new Firesheep tool that exposes a weakness in website security, letting attackers snoop on people using public networks, steal their cookies, access their accounts and pose as them on sites such as Facebook and Twitter. While the developers chose to use the Firefox add-on API, the tool could have just as easily been written and distributed as a stand-alone program.
The introduction of this tool reinforces the importance of websites configuring themselves to require secure connections.
Not too long ago we announced HTTP Strict-Transport-Security that can be used to — among other things — ensure your Facebook or Twitter cookies can’t be sniffed by someone using a tool like Firesheep. In fact, it’s built into Firefox 4. To protect their users from the this attack, a site simply needs to set the Strict-Transport-Security HTTP header when they serve you a secure log-in page, and make the rest of their site available over HTTPS. Firefox will take care of the rest: automatically fetching that site over a secure connection and blocking any third parties from seeing the unencrypted traffic.
We recommend that website authors make use of this header in order to protect their users.
But this technology is new to Firefox 4. To get HTTP Strict-Transport-Security support in Firefox 3.6, you will need to install an add-on that implements it such as ForceTLS. ForceTLS also gives you a way to opt-in to this extra security for sites who haven’t yet started sending that helpful HTTP header; it provides a user interface to add and remove sites that should never be contacted insecurely. Both HSTS and the manual opt-in are also available as part of NoScript. However, manually opting-in to HSTS on a site which does not yet make itself fully available securely may break the site; not all sites are ready for secure access.
If you are already using Firefox 4 beta or nightly versions, you can enable the additional controls with the STS-UI add-on. While the core Strict-Transport-Security features are already built into Firefox 4, this UI gives advanced users the ability to further ensure the security of their connections.