Web sites routinely incorporate JavaScript programs from several sources into
a single page. These sources must be protected from one another, which requires
robust sandboxing. The many entry-points of sandboxes and the subtleties of
JavaScript demand robust verification of the actual sandbox source. We use a
novel type system for JavaScript to encode and verify sandboxing properties.
The resulting verifier is lightweight and efficient, and operates on actual
source. We demonstrate the effectiveness of our technique by applying it to
ADsafe, which revealed several bugs and other weaknesses.Comment: in Proceedings of the USENIX Security Symposium (2011
