An issue was discovered in certain Apple products. iOS before 11.3 is affected. macOS before 10.13.4 is affected. tvOS before 11.3 is affected. watchOS before 4.3 is affected. The issue involves the "CoreText" component. It allows remote attackers to cause a denial of service (application crash) via a crafted string.
https://support.apple.com/HT208698
https://support.apple.com/HT208696
https://support.apple.com/HT208693
https://support.apple.com/HT208692