WKWebView in WebKit in Apple iOS before 10, iTunes before 12.5.1 on Windows, and Safari before 10 does not properly verify X.509 certificates from HTTPS servers, which allows man-in-the-middle attackers to spoof servers and obtain sensitive information via a crafted certificate.
Apple Security Advisory 2016-09-20-2 - Safari 10 is now available and addresses cross site scripting, code execution, and various other vulnerabilities.