An issue was discovered in certain Apple products. macOS before 10.12.3 is affected. The issue involves the "Help Viewer" component, which allows XSS attacks via a crafted web site.
https://www.exploit-db.com/exploits/41443/
https://support.apple.com/HT207483
https://bugs.chromium.org/p/project-zero/issues/detail?id=1040