VULNERABILITY DETAILS
I opened an incognito window on a notebook I do not own and logged in on Gmail and Facebook. When I finished I just closed the incognito windows without logging out on Gmail or Facebook.

When I opened the same computer a few hours later, again opened incognito mode and checked Facebook and gmail, I was still logged in. On regular (non-incognito mode) the computer's owner is logged in at the same time on these services.


VERSION
Chrome Version: 57.0.2987.133 (64-bit) + stable
Operating System: MacOS Sierra 10.12.4 (16E195) on MacBook Air (13-inch, Mid 2011)

REPRODUCTION CASE