iPhone developer Joshua Hill of the Chronic Dev Team has publicly confirmed that he is going to release an updated version of GreenPois0n with support for iOS 4.2.1 jailbreak as soon as he is done adding sandbox patches.
Updated version of greenpois0n coming whenever I finish adding these new sandbox patches, sorry this has taken so long
For those of you who don’t know, GreenPois0n is based on Geohot’s Limera1n bootrom exploit which has already pwned all current iOS devices for life. This release of GreenPois0n though will most likely be a tethered jailbreak, much like what Redsn0w 0.9.6b6 can already achieve.
This so called tethered or semi-tethered jailbreak however only applies to the new devices like: iPhone 3GS (new bootrom), iPhone 4, iPad, iPod touch 2G (MC Model), iPod touch 3G and the iPod touch 4G. Old devices like iPhone 3GS (old bootrom), iPhone 3G and iPod touch 2G (Non-MC Model) can be jailbroken-untethered right now using tools such as Redsn0w 0.9.6b6. For untethered jailbreak, you will have to use Redsn0w 0.9.7 which requires you to have SHSH blobs of iOS 4.2b3 saved.
More updates as they come! Stay tuned !