Here is an explanation of how the vulnerability works:
http://seclists.org/oss-sec/2014/q3/650

Steps to Test

1 - Please SSH into the Console of AO (Super, Worker, or Collector) as root

2 - Run the following Command:

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

Affected Output

vulnerable
this is a test

Patch Instructions

1 - cd /etc/yum.repos.d

2 - cp ../yum.repos.d.orig/CentOS-* /etc/yum.repos.d/

• NOTE:  If the above copy command does not work please run the following:
• ls -l /etc/yum.repos.d/
• Make sure CentOS-Base.repo is in this directory
• If the above file is there - Please move forward to step 3

3 - yum update bash -y

4 - Test Again:  env x='() { :;}; echo vulnerable' bash -c "echo this is a test"

Expected results

bash: warning: x: ignoring function definition attempt
bash: error importing function definition for `x'

this is a test

NOTE: Latest Bash patch will have the following result only:

this is a test