The issue, uncovered by a YouTube user who posted a video demonstrating how it can be done, allows unlocking the phone and accessing call logs, contacts, voice mails, and even allows phone calls to be made, ZDNet reported Thursday.
The phones lock can be circumvented by quickly making and cancelling an emergency call while briefly holding down the power button.
Apple is reportedly working on a fix for the bug, but said it will require a software update.
"Apple takes user security very seriously," the company told CNET. "We are aware of this issue, and will deliver a fix in a future software update."