An issue was discovered in certain Apple products. iOS before 11.1 is affected. tvOS before 11.1 is affected. watchOS before 4.1 is affected. The issue involves the "CoreText" component. It allows remote attackers to cause a denial of service (application crash) via a crafted text file.
https://support.apple.com/HT208222
https://support.apple.com/HT208220
https://support.apple.com/HT208219