Cookie Swap Party: Abusing First-Party Cookies for Web Tracking Quan Chen Panagiotis Ilia
[email protected] [email protected] North Carolina State University University of Illinois at Chicago Raleigh, USA Chicago, USA Michalis Polychronakis Alexandros Kapravelos
[email protected] [email protected] Stony Brook University North Carolina State University Stony Brook, USA Raleigh, USA ABSTRACT 1 INTRODUCTION As a step towards protecting user privacy, most web browsers perform Most of the JavaScript (JS) [8] code on modern websites is provided some form of third-party HTTP cookie blocking or periodic deletion by external, third-party sources [18, 26, 31, 38]. Third-party JS li- by default, while users typically have the option to select even stricter braries execute in the context of the page that includes them and have blocking policies. As a result, web trackers have shifted their efforts access to the DOM interface of that page. In many scenarios it is to work around these restrictions and retain or even improve the extent preferable to allow third-party JS code to run in the context of the of their tracking capability. parent page. For example, in the case of analytics libraries, certain In this paper, we shed light into the increasingly used practice of re- user interaction metrics (e.g., mouse movements and clicks) cannot lying on first-party cookies that are set by third-party JavaScript code be obtained if JS code executes in a separate iframe. to implement user tracking and other potentially unwanted capabil- This cross-domain inclusion of third-party JS code poses security ities.