Redsn0w 0.9.6rc9

The 4.3.1 untether exploit comes courtesy of Stefan Esser (@i0n1c on twitter), a security researcher based in Germany. Stefan has a long history of vulnerability research, and ironically his first contribution to the iPhone jailbreak community was improved security — last year he beat Apple to the punch and implemented ASLR for jailbroken iPhones with his “antid0te” framework. We’re happy to see that Stefan then turned his iPhone attention over to an untethered jailbreak exploit!

WARNING — ultrasn0w users don’t update yet! See a few paragraphs down!

The 4.3.1 untether works on all devices that actually support 4.3.1 except for the iPad2:
• iPhone3GS
• iPhone4 (GSM)
• iPod touch 3G
• iPod touch 4G
• iPad1
• AppleTV 2G (PwnageTool only for now)
The reason the untether won’t work as-is on the iPad2 is that it requires a bootrom or iBoot-level exploit to install, and the iPad2 is not susceptible to either the limera1n or SHAtter bootrom exploits.
WARNING WARNING — ultrasn0w users don’t update yet! We need to first release an update to ultrasn0w that fixes some incompatibilities when FW 4.3.1 is used on the older basebands supported by ultrasn0w. And remember once we do fix ultrasn0w for 4.3.1 (we’ll announce it here and on twitter), you must only get there via a custom IPSW from PwnageTool, Sn0wbreeze or xpwn! Don’t ever try to restore or update to a stock IPSW, or you’ll lose the unlock!

Link for more information: http://anonymz.com/?http://www.iphone-hacks.com/2011/04/04/redsn0w-pwnagetool-released-untethered-ios-4-3-1-jailbreak/