The Double Edged Sword: Identifying Authentication Pages and their Fingerprinting Behavior

Browser fingerprinting is often associated with cross-site user tracking, a practice that many browsers (e.g., Safari, Brave, Edge, Firefox, and Chrome) want to block. However, less is publicly known about its uses to enhance online safety, where it can provide an additional security layer against service abuses (e.g., in combination with CAPTCHAs) or during user authentication. To the best of our knowledge, no fingerprinting defenses deployed thus far consider this important distinction when blocking fingerprinting attempts, so they might negatively affect website functionality and security. To address this issue we make three main contributions. First, we introduce a novel machine learning-based method to automatically identify authentication pages (i.e. login and sign-up pages). Our supervised algorithm achieves 96-98% precision and recall on a manually-labelled dataset of almost 1,000 popular sites. Second, we compare our algorithm with methods from prior works on the same dataset, showing that it significantly outperforms all of them. Third, we quantify the prevalence of fingerprinting scripts across login and sign-up pages (10.2%) versus those executed on other pages (9.2%); while the rates of fingerprinting are similar, home pages and authentication pages differ in the third-party scripts they include and how often these scripts are labeled as tracking. We also highlight the substantial differences in fingerprinting on login and sign-up pages. Our work sheds light on the complicated reality that fingerprinting is used to both protect user security and invade user privacy; this dual nature must be considered by fingerprinting mitigations. CCS CONCEPTS • Security and privacy → Privacy protections; • General and reference → Measurement; • Computing methodologies → Classification and regression trees.