Date Added: Dec 2009
Browser extensions are remarkably popular, with one in three Firefox users running at least one extension. Although well-intentioned, extension developers are often not security experts and write buggy code that can be exploited by malicious web site operators. In the Firefox extension system, these exploits are dangerous because extensions run with the user's full privileges and can read and write arbitrary files and launch new processes. This paper analyzes 25 popular Firefox extensions and find that 88% of these extensions need less than the full set of available privileges. Additionally, one finds that 76% of these extensions use unnecessarily powerful APIs, making it difficult to reduce their privileges.