providers/settings/SettingsProvider.java in Android 6.x before 2016-09-01 and 7.0 before 2016-09-01 allows physically proximate attackers to bypass the SAFE_BOOT_DISALLOWED protection mechanism and boot to safe mode via the Android Debug Bridge (adb) tool, aka internal bug 29900345.
https://android.googlesource.com/platform/frameworks/base/+/91fc934bb2e5ea59929bb2f574de6db9b5100745
http://www.securitytracker.com/id/1036763