server/wm/WindowManagerService.java in Android 6.x before 2016-09-01 does not enforce the DISALLOW_SAFE_BOOT setting, which allows physically proximate attackers to bypass intended access restrictions and boot to safe mode via unspecified vectors, aka internal bug 26251884.
https://android.googlesource.com/platform/frameworks/base/+/69729fa8b13cadbf3173fe1f389fe4f3b7bd0f9c
http://www.securitytracker.com/id/1036763