Cross Context Scripting (XCS) is a type of XSS (Cross Site Scripting) injection which occurs from an untrusted zone, typically a web page on the Internet into the context of a trusted browser zone.
XSS injection in a trusted browser zone can be 'lethal', as injected payload runs as privileged code. No SOP (Same-Origin Policy) restrictions are enforced and direct interfacing with the underlying OS is possible.
To exploit such bugs, there is no need to use ROP gadgets, spray the heap or attempt other complex techniques. At the opposite, only few elements are required for a successful exploit, such as the right injection point and a tailored exploit payload.
This presentation will examine XCS in details and will provide a demonstration of XCS exploits of both unpatched and patched vulnerabilities in Firefox, Opera, Maxthon and Avant browsers.