There is an easily way to check whether your server is vulnerable by the following command

Once execute the command you will get an output same as below there is no vulnerable.

# cd /tmp; rm -f /tmp/echo; env 'x=() { (a)=>\' bash -c "echo date"; cat /tmp/echo


date

cat: /tmp/echo: No such file or directory

If your server is vulnerable, then the following will be displayed (with the date):
 
# cd /tmp; rm -f /tmp/echo; env 'x=() { (a)=>\' bash -c "echo date"; cat /tmp/echo


bash: x: line 1: syntax error near unexpected token `='

bash: x: line 1: `'

bash: error importing function definition for `x'

Thu Oct  2 17:05:50 IST 2014

And the file /tmp/echo will be created.

You want to update Bash on your server, execute the commands
 
# yum clean all
            
# yum -y update bash

# yum -y update

referenced from the URL