Biblio

Browser extensions are small JavaScript, CSS and HTML programs that run inside the browser with special privileges. These programs, often written by third parties, operate on the pages that the browser is visiting, giving the user a programmatic way to configure the browser. The privacy implications that arise by allowing privileged third-party code to execute inside the users' browser are not well understood. In this paper, we develop a taint analysis framework for browser extensions and use it to perform a large scale study of extensions in regard to their privacy practices. We first present a hybrid approach to traditional taint analysis: by leveraging the fact that extension source code is available to the runtime JavaScript engine, we implement as well as enhance traditional taint analysis using information gathered from static data flow and control-flow analysis of the JavaScript source code. Based on this, we further modify the Chromium browser to support taint tracking for extensions. We analyzed 178,893 extensions crawled from the Chrome Web Store between September 2016 and March 2018, as well as a separate set of all available extensions (2,790 in total) for the Opera browser at the time of analysis. From these, our analysis flagged 3,868 (2.13%) extensions as potentially leaking privacy-sensitive information. The top 10 most popular Chrome extensions that we confirmed to be leaking privacy-sensitive information have more than 60 million users combined. We ran the analysis on a local Kubernetes cluster and were able to finish within a month, demonstrating the feasibility of our approach for large-scale analysis of browser extensions. At the same time, our results emphasize the threat browser extensions pose to user privacy, and the need for countermeasures to safeguard against misbehaving extensions that abuse their privileges.

In recent years, with the advances in JavaScript engines and the adoption of HTML5 APIs, web applications begin to show a tendency to shift their functionality from the server side towards the client side, resulting in dense and complex interactions with HTML documents using the Document Object Model (DOM). As a consequence, client-side vulnerabilities become more and more prevalent. In this paper, we focus on DOM-sourced Cross-site Scripting (XSS), which is a kind of severe but not well-studied vulnerability appearing in browser extensions. Comparing with conventional DOM-based XSS, a new attack surface is introduced by DOM-sourced XSS where the DOM could become a vulnerable source as well besides common sources such as URLs and form inputs. To discover such vulnerability, we propose a detecting framework employing hybrid analysis with two phases. The first phase is the lightweight static analysis consisting of a text filter and an abstract syntax tree parser, which produces potential vulnerable candidates. The second phase is the dynamic symbolic execution with an additional component named shadow DOM, generating a document as a proof-of-concept exploit. In our large-scale real-world experiment, 58 previously unknown DOM-sourced XSS vulnerabilities were discovered in user scripts of the popular browser extension Greasemonkey.

Cross site scripting (XSS) is a kind of common attack nowadays. The attack patterns with the new technical like HTML5 that makes detection task getting harder and harder. In this paper, we focus on the browser detection mechanism integrated with HTML5 and CORS properties to detect XSS attacks with the rule based filter by using browser extensions. Further, we also present a model of composition pattern estimation system which can be used to judge whether the intercepted request has malicious attempts or not. The experimental results show that our approach can reach high detection rate by tuning our system through some frequently used attack sentences and testing it with the popular tool-kits: XSSer developed by OWASP.