tl;dr Apple Safari for OS X was prone to URI spoofing vulnerability (and more general a user interface spoofing). Apple released security updates for Safari 9 on OS X and assigned CVE-2015-5764. Accidentally this vulnerability was also present in iOS. Instant demo In Safari up to 8.0.8 : go to https://asanso.github.io/CVE-2015-5764/file0.html click "click me!" notice the address bar being "data:text/html,%3CH1%3EHi!!%3C/H1%3E" go back using the browser button click "click me!" notice the address bar being http://www.intothesymmetry.com/CVE-2015-5764/file0.php !!!! Well this looks a clear caching problem to me, right :) ? The Introduction (Oldie but goldie) Several months ago (almost a year!!) I was reading the great book written by lcamtuf (aka Michal Zalewski) named The Tangled Web . I know, I know I was a bit late for the party :) Said that, this book contained a really interesting Chapter (for the record Chapter 10) that is de