ShellShock, or Bash Bug, is a nickname for the bug in the Bash (Bourne-again Shell) command line interpreter, also known as a shell. Bash is software that has been around since 1989 and is used to control the command prompt on a variety of Unix-based systems, including Linux and Mac OS X, basically telling your computer what you want it to do. With this latest bug, outsiders could take control of the affected device to install programs or run commands. However, there are multiple types of command shells, so even if Bash is installed, the system could actually be using a different one.
If you currently use any Avocent or Liebert products through Emerson Network Power, know that they have been auditing their systems since the bug was discovered and are keeping an up-to-date log of their status. They have listed out any Avocent and Liebert branded product families that contain Bash and are providing updates for each of those products, including ones that are not directly exposed to the bug vulnerability.