Shellshock – A bug discovered in the widely used Bash command interpreter.
It does poses a critical security risk to Unix and Linux systems –and, thanks to their ubiquity, the internet at large.
More info here:
http://www.theregister.co.uk/2014/09/24/bash_shell_vuln/
Some more nice info:
https://blog.cloudflare.com/inside-shellshock/