Simon Willison’s Weblog

19th March 2018 - Link Blog

Protecting Against HSTS Abuse (via) Any web feature that can be used to persist information will eventually be used to build super-cookies. In this case it’s HSTS—a web feature that allows sites to tell browsers “in the future always load this domain over HTTPS even if the request specified HTTP”. The WebKit team caught this being exploited in the wild, by encoding a user identifier in binary across 32 separate sub domains. They have a couple of mitigations in place now—I expect other browser vendors will follow suit.