An issue was discovered in certain Apple products. iOS before 11.4 is affected. macOS before 10.13.5 is affected. tvOS before 11.4 is affected. watchOS before 4.3.1 is affected. The issue involves the "Messages" component. It allows local users to perform impersonation attacks via an unspecified injection.
https://support.apple.com/HT208851
https://support.apple.com/HT208850
https://support.apple.com/HT208849