Vulnerability in Bash Shell widespread and serious

Upgrade now, if you can. A bug discovered in the widely used Bash command interpreter poses a critical security risk to Unix and Linux systems - and, thanks to their ubiquity, the internet at large.

From the Register:

It lands countless websites, servers, PCs, OS X Macs, various home routers, and more, in danger of hijacking by hackers.

The vulnerability is present in Bash up to and including version 4.3, and was discovered by Stephane Chazelas. It puts Apache web servers, in particular, at risk of compromise: CGI scripts that use or invoke Bash in any way - including any child processes spawned by the scripts - are vulnerable to remote-code injection. OpenSSH and some DHCP clients are also affected on machines that use Bash.

Now is also a good time to wipe your servers and reinstall Minix or Plan9 as a precaution. ;)