The CFNetwork Session component in Apple iOS before 8.3 and Apple OS X before 10.10.3 does not properly handle request headers during processing of redirects in HTTP responses, which allows remote attackers to bypass the Same Origin Policy via a crafted web site.
Apple Security Advisory 2015-04-08-3 - iOS 8.3 is now available and addresses code execution, access restriction, information disclosure, and various other vulnerabilities.