You're in a potentially malicious network (free WiFi, guest network, or maybe your own corporate LAN). You're a security conscious netizen so you restrict yourself to HTTPS (browsing to HSTS sites and/or using a "Force TLS/SSL" browser extension). All your traffic is protected from the first byte. Or is it?
We will demonstrate that, by forcing your browser/system to use a malicious PAC (Proxy AutoConfiguration) resource, it is possible to leak HTTPS URLs. We will explain how this affects the privacy of the user and how credentials/sessions can be stolen. We will present the concept of "PAC Malware" (a malware which is implemented only as Javascript logic in a PAC resource) that features: a 2-way communication channel between the PAC malware and an external server, contextual phishing via messages, denial-of-service options, and sensitive data extraction from URI's. We present a comprehensive browser PAC feature matrix and elaborate more about this cross-platform (Linux, Windows, Mac) and cross-browser (IE, Chrome, Safari) threat.