The latest version of
Forbes's Andy Greenberg reports that
The bug involves using the new Control Center feature from the lock screen to access the Clock app. From there, a person can use a combination of clicks of the power and home buttons to get access to multitasking on the device.
If the Camera app has been recently used, the person then has access to photos on the device. From there, they can use iOS 7's sharing features to get to email and Twitter.
Mark Gurman has an article on 9to5Mac with the steps to replicate the bug.
Apple says it's working on a fix for the bug.
Here's a video showing the bug in action: