Protecting Browsers from Extension Vulnerabilities Adam Barth, Adrienne Porter Felt, Prateek Saxena Aaron Boodman University of California, Berkeley Google, Inc. fabarth, afelt,
[email protected] [email protected] Abstract browser’s full privileges. If an attacker can exploit an ex- tension vulnerability, the attacker can usurp the extension’s Browser extensions are remarkably popular, with one in broad privileges and install malware on the user’s machine. three Firefox users running at least one extension. Although At this year’s DEFCON, Liverani and Freeman presented well-intentioned, extension developers are often not security attacks against a number of popular Firefox extensions [24]. experts and write buggy code that can be exploited by ma- In one example, if the user dragged an image from a mali- licious web site operators. In the Firefox extension system, cious web page into the extension, the web site operator these exploits are dangerous because extensions run with could install a remote desktop server on the user’s machine the user’s full privileges and can read and write arbitrary and take control of the user’s mouse and keyboard. files and launch new processes. In this paper, we analyze These attacks raise the question of whether browser ex- 25 popular Firefox extensions and find that 88% of these tensions require such a high level of privilege. To investi- extensions need less than the full set of available privileges. gate this question, we examine 25 popular Firefox exten- Additionally, we find that 76% of these extensions use un- sions to determine how much privilege each one requires.