An issue was discovered in certain Apple products. iOS before 10.2 is affected. watchOS before 3.1.1 is affected. The issue involves the "Accounts" component, which allows local users to bypass intended authorization restrictions by leveraging the mishandling of an app uninstall.
https://support.apple.com/HT207487
https://support.apple.com/HT207422
https://lists.apple.com/archives/security-announce/2016/Dec/msg00001.html