Apple has released security update OS X Bash Update 1.0.
The patch is available as three separate downloads for OS X Mavericks 10.9.5, OS X Mountain Lion, and OS X Lion. A patch for OS X Yosemite Public Beta and Developer Preview releases are not yet available.
The download is very small, around 3.5MB.
More information at OS X Daily: http://osxdaily.com/2014/09/29/os-x-bash-update-1-0-shellshock-patch/