A flaw was found in the way Bash evaluated certain specially crafted environment variables. An attacker could use this flaw to override or bypass environment restrictions to execute shell commands. Certain services and applications allow remote unauthenticated attackers to provide environment variables, allowing them to exploit this issue.
Red Hat has a command you can use to test if you’re vulnerable, along with some nice details.
Update bash on your boxes, or if you can’t, shut down SSH and block it with your firewall rules.
On FreeBSD, uninstall it and make tcsh your friend again.