GNU Bash (Bourne Again SHell) is a command shell commonly used on Linux and Unix systems.
The Bash shell executes commands injected after function definitions contained in environment variables. This could be used by a remote attacker to cause arbitrary commands to execute if a web server hosts programs which invoke the Bash shell.
Apply updated Bash packages from the Linux or Unix vendor.
This exploit requires the path to a web program which invokes the Bash shell. This attack vector may not exist on all systems with affected versions of Bash, and other attack vectors may exist which are not covered by this exploit.