CNN Report on Microsoft Vulnerability
and until Microsoft gets a patch out (RSN, really) you can find a fix here:
If you're interested in a detailed explanation of why this needs to be patched now, instead of waiting for the official patch, please check out:
SANS Internet Storm Center - Cooperative Cyber Threat Monitor and Alert system: WMF: Patches and workarounds explained
I should probably put a disclaimer in here about how applying any patch to you system is changing it and change can be bad on un-backed up systems, do this at your own risk,
But guys, read the articles, you'll get as scared as I am and apply the patches.