In this paper we examine security issues of functionality extension mechanisms supported by web browsers. Extensions (or "plug-ins") in modern web browsers enjoy unrestrained access at all times and thus are attractive vectors for malware. To solidify the claim, we take on the role of malware writers looking to assume control of a user's browser space. We have taken advantage of the lack of security mechanisms for browser extensions and implemented a malware application for the popular Firefox web browser, which we call browserSpy, that requires no special privileges to be installed. browserSpy takes complete control of the user's browser space, can observe all activity performed through the browser and is undetectable. We then adopt the role of defenders to discuss defense strategies against such malware. Our primary contribution is a mechanism that uses code integrity checking techniques to control the extension installation and loading process. We describe two implementations of this mechanism: a drop-in solution that employs JavaScript and a faster, in-browser solution that makes uses of the browser's native cryptography implementation. We also discuss techniques for runtime monitoring of extension behavior to provide a foundation for defending threats posed by installed extensions.

In this paper we examine the security issues in functionality extension mechanisms supported by web browsers. Extensions (or "plug-ins") in modern web browsers enjoy unlimited power without restraint and thus are attractive vectors for malware. To solidify the claim, we take on the role of malware writers looking to assume control of a user's browser space. We have taken advantage of the lack of security mechanisms for browser extensions and have implemented a piece of malware for the popular Firefox web browser, which we call BROWSER-SPY, that requires no special privileges to be installed. Once installed, BROWSER-SPY takes complete control of a user's browser space and can observe all the activity performed through the browser while being undetectable. We then adopt the role of defenders to discuss defense strategies against such malware. Our primary contribution is a mechanism that uses code integrity checking techniques to control the extension installation and loading process. We also discuss techniques for runtime monitoring of extension behavior that provide a foundation for defending threats due to installed extensions.