An issue was discovered in certain Apple products. iOS before 11 is affected. Safari before 11 is affected. iCloud before 7.0 on Windows is affected. The issue involves the "WebKit" component. It allows remote attackers to conduct Universal XSS (UXSS) attacks via a crafted web site that is mishandled during parent-tab processing.
https://support.apple.com/HT208142
https://support.apple.com/HT208116
https://support.apple.com/HT208112
http://www.securitytracker.com/id/1039385