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Vulnerability-driven filtering of network data can offer a fast and easy-to-deploy alternative or intermediary to software patching, as exemplified in Shield 43. In this paper, we take Shield’s vision to a new domain, inspecting and cleansing not just static content, but also dynamic content. The dynamic content we target is the dynamic HTML in web pages, which have become a popular vector for attacks. The key challenge in filtering dynamic HTML is that it is undecidable to statically determine whether an embedded script will exploit the browser at run-time. We avoid this undecidability problem by rewriting web pages and any embedded scripts into safe equivalents, inserting checks so that the filtering is done at run-time. The rewritten pages contain logic for recursively applying run-time checks to dynamically generated or modified web content, based on known vulnerabilities. We have built and evaluated BrowserShield, a system that performs this dynamic instrumentation of embedded scripts, and that admits policies for customized run-time actions like vulnerabilitydriven filtering. 1
Reis et al. (Mon,) studied this question.