A cookie management issue was addressed with improved checks. This issue affected versions prior to iOS 11.4.1, macOS High Sierra 10.13.6, tvOS 11.4.1, watchOS 4.3.2, iTunes 12.8 for Windows, iCloud for Windows 7.6.
https://support.apple.com/kb/HT208932
https://support.apple.com/kb/HT208933
https://support.apple.com/kb/HT208935
https://support.apple.com/kb/HT208936