Self-healing Javascript Errors Caused by the Browser Extension Privacy Badger

Sammanfattning: As today’s web is filled with privacy-invasive third-party trackers, users are turning to privacy extensions to prevent their browsing habits from leaking. However, research has shown that privacy extensions can decrease website quality and even break meaningful functionality. Our research addresses this problem by performing automated repairs on Javascript code that has been broken by Privacy Badger, a heuristics-based privacy extension. First, we study how the use of Privacy Badger affects the prevalence of Javascript errors on 11 665 urls. We find errors caused by Privacy Badger on 758 (6.5%) urls. We also observe a 74% increase in Javascript errors, and a 27% increase in urls affected by Javascript errors when browsing with Privacy Badger. Using this data, we investigate how BikiniProxy, an automated HTML and Javascript rewriting proxy consisting of five self-healing strategies, performs on errors caused by Privacy Badger. Out of 751 web pages with errors caused by Privacy Badger, 215 (29%) had at least one such error healed by BikiniProxy. Additionally, we recognize a shortcoming of BikiniProxy’s line skipper strategy, and propose an improvement to it. Repairing web pages using our modified version of BikiniProxy reduces the number of errors on 12.9% more urls. Finally, we show that repairing errors using BikiniProxy can restore functionality that has been broken by Privacy Badger. But we can only detect such cases in two urls out of the hundreds repaired, which shows that the repair approach suffers from overfitting in our context. Our most important insight is that privacy extensions can break functionality without blocking any resource that the functionality is dependent on, and that these are the cases where BikiniProxy can restore the functionality.