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Memento: A Framework for Hardening Web Applications

ABSTRACT We propose a generic framework called Memento for systematically hardening web applications. Memento models a web application's behavior using a deterministic finite automata (DFA), where each server-side script is a state, and state transitions are triggered by HTTP requests. We use this DFA to defend against cross-site request forgery (CSRF) and cross-site-scripting (XSS) attacks. The client web browser and the application server each maintain a view of the application state. XSS and CSRF attacks either create an interaction that does not conform to the interaction model or force the web applica-tion's view of the state to diverge from the user's view. Memento derives behavior models directly from the application, and limits all run-time interactions to the derived interaction models, flagging any state divergence as an attack. We implemented Memento for the Apache web server and evaluated it using 8 open source web applications. We created Memento instances for the 8 web applications and verified Memento's defense on 14 CSRF and 46 XSS attacks. Memento was able to detect all the attacks with zero false positives and a performance overhead of 28%. Memento does not require any modifications in the web applications it protects.

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May 28, 2014