http://alblue.bandlem.com/2014/09/bash-remote-vulnerability.html
As you’ve probably heard, there’s a remote vulnerability in Bash, which means that an attacker can supply a malicious code by virtue of passing in an environment variable with a specially crafted value that is then executed by Bash when a new shell starts up. This could potentially give an attacker control over an account running requests, which could include any HTTP request (variables such as REMOTE_HOST are passed through to CGI scripts by default) as well as certain environment variables in SSH (such as TERM).
I have written about this more at InfoQ, and most major operating system vendors have published updates to their versions of Bash.
Apple typically take time to fix these issues, so in the meantime, if you have an OSX server estate you are advised to upgrade to a new version of bash immediately.
If you have the Xcode developer tools available, you can compile it yourself as follows:
