providers/settings/SettingsProvider.java in Android 7.0 before 2016-09-01 does not properly enforce the DISALLOW_CONFIG_VPN setting, which allows attackers to bypass an intended always-on VPN state via a crafted application, aka internal bug 29899712.
https://android.googlesource.com/platform/frameworks/base/+/335702d106797bce8a88044783fa1fc1d5f751d0
http://www.securitytracker.com/id/1036763