Because of its wide distribution, the vulnerability could be as wide-ranging and as potentially dangerous as the Heartbleed bug. The vulnerability affects versions 1.14 through 4.3 of GNU Bash. Patches have been issued by many of the major Linux distribution vendors for affected versions, including:

Red Hat Enterprise Linux (versions 4 through 7) and the Fedora distribution
CentOS (versions 5 through 7)
Ubuntu 10.04 LTS, 12.04 LTS, and 14.04 LTS
Debian
...
There is an easy test to determine if a Linux or Unix system is vulnerable. To check your system, from a command line, type:

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

If the system is vulnerable, the output will be:

vulnerable this is a test