Just when Apple thought they were out of the woods, a new lockscreen vulnerability has been discovered. Apple released iOS 6.1.3 to fix a previously found lockscreen vulnerability, though it appears to have introduced a new one--or failed to fix one that was present in previous versions.
The bug isn't too difficult to activate, nor is it difficult to protect from. A person needs to simply make a telephone call by using Siri and remove the SIM card at the correct time. The bypass is demonstrated in the above embedded video.
To protect against the bypass until Apple fixes it, you just have to disable voice dial from the Password Lock screen. It's time for Apple to start working on iOS 6.1.4.