Nyan. Download the newest version of redsn0w from the dev-team blog:
Dev-Team Blog
Download the 6.0 IPSW for your device on this page:
iClarified - iPhone - Where To Download iPhone Firmware Files From
Make sure you get the 6.0, not the 6.1.3.
Choose Extras in redsn0w and IPSW. Select the 6.0 IPSW.
Go back to the first page in redsn0w. Choose jailbreak. Follow the onscreen instructions.
If it gives you issues, go back to Extras, choose Just boot. Try the jailbreak again. It's a bit feisty as it isn't officially supported and is just the workaround.
In order to maintain jailbreak tweaks, after any power cycle you'll need to plug back into redsn0w and use that "Just Boot" option. Otherwise you'll be able to boot, but won't maintain jailbreak functionality.