Recently there has been the new vulnerability on bash in unix system allowing unauthenticated access to applications and services to atackers. Following are quick steps as displayed on Red hat support portal to identify whether your RHEL/CentOS is vulnerable or not.
Go to command prompt then type the following command:
env 'x=() { :;}; echo vulnerable' 'BASH_FUNC_x()=() { :;}; echo vulnerable' bash -c "echo test"
If you see in the result some word like “vulnerable” then you need to update your bash to the latest or rater patched version.
To be on the safer side please keep your bash updated with latest fixes
yum update bash
Further Reading:
https://access.redhat.com/articles/1200223?sc_cid=70160000000e8eaAAA