Content Security Policy

Why not let domains specify what should be loaded from their websites? This idea has been proposed as a "Content Security Policy" [3]. Unfortunately, the project is new and hasn't gained a lot of traction (on the plus side, there is a working specification and an example add-on for Firefox to implement). In the future, one hopes this project will become more mainstream.

Here Comes Linux

If you can't globally disable JavaScript and if controlling it on a domain-by-domain basis is hit or miss, how are you supposed to surf the web safely and have access to JavaScript-based websites? By using the power of Linux, of course! Chances are good that if you're reading this magazine, you're using Linux (if not, be amazed at how simply a complicated problem can be solved).

Multi-User OS(Linux) + xhost

If you're running the X Window System (XFree86, which begat Free Desktop, which is what you're probably running), you're running a desktop that was designed to, among other things, allow different users and even systems to run and display programs on the desktop. The X server renders and displays the information to the user. The X client runs the program and sends the data to be displayed to the X server. To allow other local users and remote systems to interact safely with the X server on a given host, access controls are implemented. With the program xhost [4], you can manipulate these access controls. If you want to browse the web without worrying about a remote site executing hostile code and taking over your box, simply create a new user for the express purpose of running Firefox. The new user will have permission to run and display programs on your desktop:

Setup (as root):
# adduser webuser
# passwd webuser
Setup (as yourself):
$ xhost +SI:localuser:webuser

This code adds and sets a password for a user called webuser. Next, it adds access for the webuser account that allows programs to run and display on your monitor with the use of xhost.

Log in as the "webuser" account
$ su -- webuser [enter password]
Run firefox
$ firefox

When you want to surf the web, you can just open a terminal, use su to change to the web user you have created, and then run Firefox, which will execute and display to the monitor as it normally would. If you wanted to go an extra step, you could run and configure Firefox (installing add-ons, saving passwords, etc.) and then tar up the web user's home directory. After running Firefox, you would simply blow the home directory away and restore it:

Create a backup
# cd /home/
# tar --cvf webuser.tar /webuser
Restore the backup
# rm --rf /home/webuser
# tar --xvf /home/webuser.tar --C /home/

Anything an attacker has done to compromise that account will be removed (unless the attacker has launched a second attack against the local system, but this is unlikely).

Of course, any changes you have made in Firefox are lost. Although this is not the most seamless way to go, it is very effective. Unless an attacker manages to execute code and then launch a local attack against your system to elevate privileges, he will be booted off the next time you refresh the account.