iOS 6 beta 3 has been available to registered developers for a matter of hours, and already the software has a tethered jailbreak courtesy of the iPhone Dev-Team. Like previous beta jailbreaks, however, this will not install Cydia on your device.
The Dev-Team announced the update on its website:
The “dev3″ version covers today’s 6.0beta3 release (and also adds explicit support for 6.0beta2). Please point redsn0w at the 6.0b3 IPSW in order tojailbreak beta3 and boot tethered.
To perform the jailbreak, you just need to latest version of Redsn0w (0.9.13dev3) and the iOS 6 beta 3 IPSW file. Of course, you need to be a registered developer to obtain the latter, and if you attempt to install it without UDID activation you could end up with a bricked device that you then need to downgrade.
Again, this jailbreak won’t install Cydia, largely due to the fact that almost all the packages it features don’t yet support iOS 6. And it’s a tethered solution, which means you’ll need to ensure your device is plugged into your computer every time you need to boot it up.
With that said, this isn’t a jailbreak for the average user. It’s intended for developers only who need SSH access, so we’d advice you to avoid it until iOS 6 is released and a full user jailbreak arrives. It’s not going to give you access to all your favorite tweaks, so you can probably manage without it anyway.
Source: iPhone Dev-Team