The method for bypassing the lock screen was documented in a handy video by the folks over at the Jailbreak Nation (above). It involves making -- and then immediately canceling -- an emergency call and holding down the power button a couple of times during the process.
By following the precise steps in the video, anyone can view and modify contacts, listen to your voicemail, and browse your photos (by attempting to add a photo to the accessible contact list). It doesn't appear as if the exploit grants access to email or the web.
AppleInsider was able to verify the glitch using an AT&T model iPhone 5 running iOS 6.1.
Coincidentally, a nearly identical vulnerability reared its ugly head back in October of 2010 when it was discovered that a glitch in iOS 4.1 similarly allowed anyone to access contacts, call history and voicemail on a passcode-locked handset without knowing the numeric entry code required to formally unlock the phone.
The precise steps to reproduce the bypass, for those readers without video access, are as follows:
1. Lock device
2. Slide to unlock
3. Tap emergency call
4. Hold sleep button until the power down prompt shows. Click cancel, you will notice the status bar turn blue. Type in 211 or your emergency number and click call then cancel it asap so the call dosen?t go through.
5. Lock your device with the sleep button then turn it on using the home button.
6. Slide to unlock then hold the sleep button and in 3 seconds tap emergency call. This will cause a conflict in the phone's firmware and cause it to open.