The most recent security vulnerability news is here. Bash can be used by an attacker to launch malicious code on the server. There’s a simple script to know if your server can be exploited.

env X="() { :;} ; echo shellshock" /bin/sh -c "echo completed"
env X="() { :;} ; echo shellshock" `which bash` -c "echo completed"

CentOS has just released it’s security update

Everyone on CentOS should do a simple yum update