redsn0w 0.9.6 Beta 2 can jailbreak Golden control build of iOS 4.2.
Statement of hacker proof that:
"Today Apple released to developers the GM seed for 4.2. Tinkerers will find that yesterday’s redsn0w jailbreaks today’s 4.2 GM seed, simply by pointing redsn0w at the 4.1 IPSW.Right now it mostly only makes sense for JB app developers to do that because many apps need to be updated for 4.2. However, if all you want to do is enable afc2, or to tweak settings like Battery % and Homescreen wallpapers, then go for it."