The advent of Web 2.0 has lead to the proliferation of client-side code that is typically written in JavaScript. This code is often combined or mashed-up with other code and content from disparate, mutually untrusting parties, leading to undesirable security and reliability consequences. This paper proposes GATEKEEPER, a mostly static approach for soundly enforcing security and reliability policies for JavaScript programs. GATEKEEPER is a highly extensible system with a rich, expressive policy language, allowing the hosting site administrator to formulate their policies as succinct Datalog queries. The primary application of GATEKEEPER is in reasoning about JavaScript widgets such as those hosted by widget portals Live.com and Google/IG. Widgets submitted to these sites can be either malicious or just buggy and poorly written, and the hosting site has the authority to reject the submission of widgets that do not meet the site’s security policies. To show the practicality of our approach, we describe nine representative security and reliability policies. Statically checking these policies results in 1,341 verified warnings in 684 widgets, no false negatives, due to the

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. 1