Fix Bash shell vulnerability under Linux OS .

If some Bash code outside of the curly brace then it will then be executed by the linux system.

env x='() { :;}; echo vulnerable' bash -c " bash test "

If your system is vulnerable, it will then output:

vulnerable
bash test 

How Do You Fix It ? Just open up a terminal, and type:

sudo apt-get update
sudo apt-get upgrade

or under Fedora with :

sudo yum update

Also you can see more about linux and linux tutorials here.