An inconsistent user interface issue was addressed with improved state management. This issue is fixed in macOS High Sierra 10.13.1, Security Update 2017-001 Sierra, and Security Update 2017-004 El Capitan, watchOS 4.3, iOS 12.1. Processing a maliciously crafted text message may lead to UI spoofing.
Apple Security Advisory 2018-10-30-1 - iOS 12.1 is now available and addresses code execution, cross site scripting, denial of service, and resource exhaustion vulnerabilities.