After You, Please: Browser Extensions Order Attacks and Countermeasures
This addresses a security vulnerability in browser extensions that affects millions of users, but it is incremental as it builds on known risks without introducing a new paradigm.
The paper tackles the problem of malicious browser extensions exploiting execution order to access private information from other extensions, demonstrating that an unprivileged extension can achieve this and proposing a countermeasure extension that effectively protects users against usual and strong attackers.
Browser extensions are small applications executed in the browser context that provide additional capabilities and enrich the user experience while surfing the web. The acceptance of extensions in current browsers is unquestionable. For instance, Chrome's official extension repository has more than 63,000 extensions, with some of them having more than 10M users. When installed, extensions are pushed into an internal queue within the browser. The order in which each extension executes depends on a number of factors, including their relative installation times. In this paper, we demonstrate how this order can be exploited by an unprivileged malicious extension (i.e., one with no more permissions than those already assigned when accessing web content) to get access to any private information that other extensions have previously introduced. Our solution does not require modifying the core browser engine as it is implemented as another browser extension. We prove that our approach effectively protects the user against usual attackers (i.e., any other installed extension) as well as against strong attackers having access to the effects of all installed extensions (i.e., knowing who did what). We also prove soundness and robustness of our approach under reasonable assumptions.