iOS 6.1.2 dropped today, and fixes certain issues with Exchange sync. It was assumed by many that this update would also patch the hole that was being used to jailbreak devices, but that wasn’t the case. Either because Apple doesn’t care, or because they haven’t been able to implement a stable fix, the exploit remains open. The Evad3rs today updated their Evasi0n jailbreak tool to work with iOS 6.1.2, bringing the version number to 1.4.
To update a jailbroken device, simply download and restore to the new firmware. Note that it is always a good idea to backup before restoring a device to prevent data loss, though be aware that any Cydia apps or tweaks will not carry over after the update. After the update is over, simply run Evasi0n again and – voila – your device is jailbroken again. Proceed to install any tweaks, apps, or themes you had before the update.
Also of note: if you don’t have issues with Exchange, then you can probably feel free to skip this update. No mission-critical bugs are fixed (the lockscreen bypass bug is still present), and the Exchange bug only affects a limited number of users.