GTK+ 3.10.9 and earlier, as used in cinnamon-screensaver, gnome-screensaver, and other applications, allows physically proximate attackers to bypass the lock screen by pressing the menu button.
https://github.com/linuxmint/cinnamon-screensaver/issues/44
https://bugzilla.redhat.com/show_bug.cgi?id=1064695
https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=759145
http://www.ubuntu.com/usn/USN-2475-1
http://seclists.org/oss-sec/2014/q1/331