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Xiang Pan § , Yinzhi Cao † , Yan Chen §

I Do Not Know What You Visited Last Summer: Protecting users from stateful third-party web tracking with TrackingFree browser. Xiang Pan § , Yinzhi Cao † , Yan Chen §. § Northwestern University † Columbia University. Roadmap. Background System Design Evaluation Summary. Tracker

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Xiang Pan § , Yinzhi Cao † , Yan Chen §

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  1. I Do Not Know What You Visited Last Summer: Protecting users from stateful third-party web tracking with TrackingFree browser Xiang Pan§, Yinzhi Cao†, Yan Chen§ § Northwestern University † Columbia University

  2. Roadmap • Background • System Design • Evaluation • Summary

  3. Tracker (doubleclick) User Referer : http://online.wsj.com/ Cookie : id = 12345 Referer : http://www.cnn.com/ Cookie : id = 12345 visit visit

  4. Web tracking is serious • Prevalent • More than 90% of Alexa Top 500 web sites [Roesner, NSDI 2012] • A web page usually has multiple tracking elements • “There is no such thing as anonymous online tracking” --- Arvind Narayanan • Not only browsing history, but also other sensitive information: location, name, email, … • Leaked out information can be correlated together 4

  5. No effective defense approach • Disable third-party cookie • Can be easily bypassed • Blacklist-based anti-tracking tools • Priori knowledge of tracking server • Do-not-track header • No enforcement 5

  6. TrackingFree Goals and Challenges • Anti-tracking Completeness • Functionality/compatbility • Performance Referer : http://online.wsj.com/ Cookie : id = 12345 Referer : http://www.cnn.com/ Cookie : id = 24578 Core Idea : TrackingFree partitions client-side states into multiple isolation units so that the identifiers still exists but not unique any more!

  7. Out-of-scope threats • TrackingFree doesn’t address following threats: • Within-Site Tracking. • Tracking by exploiting browser vulnerabilities • Stateless tracking.

  8. Roadmap • Background • System Design • Evaluation • Summary

  9. Architecture

  10. Contents Allocation Mechanism • Initial Contents Allocation • Handles those top frames that are navigated by users directly • Derivative Contents Allocation • Handles those frames that are generated due to the contents on other frames, which we call child frame 10

  11. Initial Contents Allocation 11

  12. Derivative Contents Allocation • Principal Switch • Should we switch principle for child frame? • Principal Selection • How to choose target principal? 12

  13. Principal Switch Same principal Different principal • The deficiencies of two intuitive yet extreme policies： • Not privacy-preserving (no switch) • Unnecessary overhead (too much switch) • Our solution: switch principal only if the following two conditions are met: • Cross-site • User-triggered 13

  14. Principal Selection • The deficiency of two intuitive yet extreme policies • Break compatibility (always create new principal) • Break anti-tracking capacity (create at most one principal for each domain) • Our solution: • Maintains an in-degree-bounded graph for principals • The in-degree of the graph is set to two 14

  15. Principal Communication • Explicit communication is widely used, but break the isolation mechanism. • Our solution: we restrict the use of explicit communication as follows: • Third-party elements in one principle can not explicitly communicate with other principals. • First-party elements can only explicitly communicate with the first-party elements placed in its neighbor principals 3119 4852 6 0 15

  16. Principal Communication • Implicit Communication • History Sharing • UI history manager • Accepts information from other managers • Only UI manager gets associated with browser UI • Communication through navigation URL 16

  17. Preference Configure • User preference can be abused to store tracking identifier. (e.g. strict transport security) • Completely isolating user preference affects user preference. • Our solution: • Isolate user preference. • Apply user-initiated changes to all of the principals. • Monitor GUI message to determine user-initiated preference change. 17

  18. Roadmap • Background • System Design • Evaluation • Summary

  19. Evaluation • Anti-tracking capability • Formal proof • Experiments with real world websites • Performance • Overhead (latency, memory, disk) • Compatibility

  20. Formal Proof • Use Alloy to formally analyzeTrackingFree ’s anti-tracking ability. • Alloy is the most popular formal proof system • Describe TrackingFree’s behaviors on an existing Alloy Web model [Akhawe et al. CSF 2010]. • Formally verified trackers can correlate TrackingFree user’s activities up to three principals without site collaboration. • Assumptions: • Non-tracking servers will not set tracking identifiers for third-party trackers. • On non-tracking host web sites, first-party elements will not send third-party tracking identifiers to other principals.

  21. Gathered tracking tokens on Alexa Top web sites by following the tracker detection of [Roesner et al. NSDI 2012]. • Detection based on the observation that each tracking request must contain the user’s globally unique identifier. • Some false negative, no false positive. Anti-tracking Capabilitywith Real World Web Sites 21

  22. Visit 2,032 valid URLsfrom Alexa Top 500 web sites. • Gathered 647 tracking tokens • TrackingFree eliminated all of them. Anti-tracking Capabilitywith Real World Web Sites Top 10 Tracking Hosts 22

  23. Performance Overall Overhead: ~3% - ~20% (2). Address Bar Navigation with Principal Avg. Overhead 3.36% (3). Cross Site Navigation Avg. Overhead 19.43% (4). Within-site Navigation Avg. Overhead 4.70% (1). Address Bar Navigation without Principal Avg. Overhead 8.29%

  24. Memory/Disk Overhead Memory Overhead on 12 Web Pages (~25MB/Principal) Disk Overhead on 12 Web Pages (~0.6MB/Principal)

  25. Compatibility • Manually tested TrackingFree’s compatibility on Alexa Top 50 websites • Compatibility on first-party websites • Results: 50/50 • Compatibility on third-party services • Cross-site online payments (1/1) • Cross-site content sharing (31/31) • Single sign-on (35/36) • Overall results: 67/68

  26. Case study: Logging Yahoo using Facebook Account 26

  27. Roadmap • Background • System Design • Evaluation • Summary 27

  28. Summary • We designed and implemented TrackingFree browser that completely protect users from third-party web tracking by isolating resources in different principals. • We theoretically and experimentally proved TrackingFree’s anti-tracking capability. • TrackingFree incurs affordable overhead and compatibility cost.

  29. Thanks & Questions?http://list.cs.northwestern.edu/WebSecurity

  30. Domain Data Manager • Backup slides…

  31. Related Work • Existing Anti-tracking Mechanisms • Do Not Track(DNT)： almost useless • Blacklist-based Tool: require priori knowledge • Disabling Third-party Cookie: easy to bypass • Existing Multi-principal Browsers • No anti-tracking capability

  32. Related Work

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