Some sites that will test urls for various methods of exploiting this:
http://www.shellshocktest.com/
http://shellshock.brandonpotter.com/
http://bashsmash.ccsir.org/
Can't 100% vouch for the trustworthiness of these sites and what they do with the test results, so use of your own back. Don't think there will be any issues using them though.
If you are using debian or Ubuntu and are worried doing all the upgrades may break things, you can use this to just update bash:
Code:
sudo apt-get update && sudo apt-get install --only-upgrade bash