GreenPois0n should be updated to support 4.2.1 (tethered or semitethered) within a few days.
What’s more, the Dev-Team has just posted a summary of what today’s iOS release means for users, and it looks like limera1n is a-go for 4.2.1, and an updated version should be available later today (“barring any unforeseen problems”).
The best news of all is for owners of iPhone3G, older iPhone3GS, and non-MC iPod touch 2G. Due to a combination of our original pwnage2 exploit, the arm7_go exploit, 24kpwn, and limera1n, your device is “just as jailbreakable as ever.” You reap the full benefit of an untethered 4.2.1 jailbreak.
Next are the owners of all the more recent devices. The good news there is that due to geohot’s limera1n exploit, all recent devices can be jailbroken (this will be true until Apple released new hardware that fixes geohot’s limerain exploit in the bootrom).
So when does all this 4.2.1 jailbreak action happen? Well if you’re a JB developer or tinkerer, you’ve already probably used the redsn0w mentioned in our last post to jailbreak 4.2.1 and at least get SSH working. But beyond that, there are still some last minute issues with MobileSubstrate and comex’s kernel patches that are being fixed. We’ll tweet and post a blog update when it’s all available (we hate to give ETAs, but barring any unforeseen problems, probably later today).
Remember, backup your SHSH blobs using TinyUmbrella (which will be updated tonight).