Cross-Origin JavaScript Capability Leaks: Detection, Exploitation, and Defense

We identify a class of Web browser implementation vulnerabilities, cross-origin JavaScript capability leaks, which occur when the browser leaks a JavaScript pointer from one security origin to another. We devise an algorithm for detecting these vulnerabilities by monitoring the “points-to” relation of the JavaScript heap. Our algorithm finds a number of new vulnerabilities in the opensource WebKit browser engine used by Safari. We propose an approach to mitigate this class of vulnerabilities by adding access control checks to browser JavaScript engines. These access control checks are backwardscompatible because they do not alter semantics of the Web platform. Through an application of the inline cache, we implement these checks with an overhead of 1–2% on industry-standard benchmarks.