Securing JavaScript Information Flow with Staged Approach

This content discusses the challenges of third-party code affecting sensitive data in JavaScript and proposes a staged approach for securing information flow, emphasizing server-side context and policies to enforce confidentiality and integrity. The solution involves analyzing JavaScript staging to ensure no unauthorized data read or write operations occur, providing a syntactically enforceable method for improved security.

• JavaScript Security
• Information Flow
• Staged Approach
• Server-side Policies

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1. Staged Information Flow for JavaScript Ravi Chugh, Jeff Meister, Ranjit Jhala, Sorin Lerner UC San Diego

2. wsj.com <textbox id= SearchBox > <button onclick= doSearch(SearchBox.value) > <script type= javascript > searchUrl = wsj.com/search? ; doSearch = function(s) { var u = searchUrl + s; document.location = u; } z = get( a.com/ad.js ); eval(z); </script> 2

3. wsj.com <textbox id= SearchBox > <button onclick= doSearch(SearchBox.value) > <script type= javascript > searchUrl = wsj.com/search? ; doSearch = function(s) { var u = searchUrl + s; document.location = u; } a.com/ad.js displayAd = function() { ... } displayAd(); </script> 3

4. wsj.com <textbox id= SearchBox > <button onclick= doSearch(SearchBox.value) > <script type= javascript > searchUrl = wsj.com/search? ; doSearch = function(s) { var u = searchUrl + s; document.location = u; } a.com/ad.js displayAd = function() { ... } displayAd(); searchUrl = evil.com/ ; </script> 4

5. evil.com Script navigates to malicious page Exploits browser vulnerability 5

6. The Problem, Part 1 Third-party code may affect sensitive data e.g. writing doc.location e.g. reading doc.cookie Information flow policies e.g. integrity of doc.location e.g. confidentiality of doc.cookie JavaScript difficulties dynamic typing first-class functions objects, but no classes prototypes server code var doc = ...; third-party code doc.location = evil ; steal(doc.cookie); 6

7. The Problem, Part 2 Entire code not available until runtime server code Arrives in stages var doc = ...; third-party code doc.location = evil ; steal(doc.cookie); 7

8. Our Staged Approach: Server context Information Flow Policies Confidentiality policy: x should not be read policy Integrity policy: x should not be written 8

9. Our Staged Approach: Server context residual policy JavaScript Staging Analysis No Write No Read policy must-not-write vars must-not-read vars Summarizes how loaded code must behave Syntactically enforceable for speed 9

10. Our Staged Approach: Client Browser context JavaScript Engine residual policy Residual Policy Checker hole 10

11. wsj.com <textbox id= SearchBox > <button onclick= doSearch(SearchBox.value) > <script type= javascript > document.location searchUrl = wsj.com/search? ; No Write s searchUrl SearchBox.value doSearch = function(s) { var u = searchUrl + s; document.location = u; } No Read doSearch </script> 11

12. wsj.com <textbox id= SearchBox > <button onclick= doSearch(SearchBox.value) > <script type= javascript > document.location searchUrl = wsj.com/search? ; No Write searchUrl SearchBox.value doSearch = function(s) { var u = searchUrl + s; document.location = u; } No Read doSearch </script> 12

13. wsj.com <textbox id= SearchBox > <button onclick= doSearch(SearchBox.value) > <script type= javascript > document.location searchUrl = wsj.com/search? ; No Write searchUrl a.com/ad1.js SearchBox.value doSearch = function(s) { var u = searchUrl + s; document.location = u; } No Read displayAd = function() { if (version < 7) { ... } else { ... } } displayAd(); doSearch </script> 13

14. wsj.com <textbox id= SearchBox > <button onclick= doSearch(SearchBox.value) > <script type= javascript > document.location searchUrl = wsj.com/search? ; No Write searchUrl a.com/ad2.js SearchBox.value doSearch = function(s) { var u = searchUrl + s; document.location = u; } No Read searchUrl = evil.com/ ; doSearch </script> 14

15. wsj.com <textbox id= SearchBox > <button onclick= doSearch(SearchBox.value) > <script type= javascript > document.location searchUrl = wsj.com/search? ; No Write searchUrl a.com/ad3.js SearchBox.value doSearch = function(s) { var u = searchUrl + s; document.location = u; } No Read doSearch( foo ); doSearch </script> 15

16. Outline Overview JavaScript Static Analysis Computing Residual Policies Additional Challenges Evaluation 16

17. Information Flow Graph Analysis tracks information flow in program Flow-insensitive, set constraint-based Graph representation: program constants, variables, edges 0 x special nodes for function declarations and calls Fun 17

18. searchUrl = wsj.com/search?; doSearch = function(s) { var u = searchUrl + s; document.location = u; } searchUrl = wsj.com/search? ; doSearch = function(s) { var u = searchUrl + s; document.location = u; } doSearch(SearchBox.value); doSearch(SearchBox.value); /* a.com/ad1.js */ displayAd = function() { ... }; displayAd(); 18

19. wsj.com/search? searchUrl = wsj.com/search? ; doSearch = function(s) { var u = searchUrl + s; document.location = u; } doSearch(SearchBox.value); searchUrl /* a.com/ad1.js */ displayAd = function() { ... }; displayAd(); 19

20. wsj.com/search? searchUrl = wsj.com/search? ; doSearch = function(s) { var u = searchUrl + s; document.location = u; } doSearch(SearchBox.value); searchUrl /* a.com/ad1.js */ displayAd = function() { ... }; displayAd(); s Fun doSearch 20

21. wsj.com/search? searchUrl = wsj.com/search? ; doSearch = function(s) { var u = searchUrl + s; document.location = u; } doSearch(SearchBox.value); searchUrl /* a.com/ad1.js */ displayAd = function() { ... }; displayAd(); u s Fun doSearch 21

22. wsj.com/search? searchUrl = wsj.com/search? ; doSearch = function(s) { var u = searchUrl + s; document.location = u; } doSearch(SearchBox.value); searchUrl /* a.com/ad1.js */ displayAd = function() { ... }; displayAd(); u s Fun doSearch document.location 22

23. wsj.com/search? searchUrl = wsj.com/search? ; doSearch = function(s) { var u = searchUrl + s; document.location = u; } doSearch(SearchBox.value); searchUrl /* a.com/ad1.js */ displayAd = function() { ... }; displayAd(); u s Fun doSearch SearchBox.value Fun document.location 23

24. wsj.com/search? searchUrl = wsj.com/search? ; doSearch = function(s) { var u = searchUrl + s; document.location = u; } doSearch(SearchBox.value); searchUrl /* a.com/ad1.js */ displayAd = function() { ... }; displayAd(); u s Fun doSearch SearchBox.value Fun document.location 24

25. wsj.com/search? searchUrl = wsj.com/search? ; doSearch = function(s) { var u = searchUrl + s; document.location = u; } doSearch(SearchBox.value); searchUrl /* a.com/ad1.js */ displayAd = function() { ... }; displayAd(); u s Fun Fun doSearch displayAd SearchBox.value Fun document.location 25

26. wsj.com/search? searchUrl = wsj.com/search? ; doSearch = function(s) { var u = searchUrl + s; document.location = u; } doSearch(SearchBox.value); searchUrl /* a.com/ad1.js */ displayAd = function() { ... }; displayAd(); u s Fun Fun doSearch displayAd SearchBox.value Fun Fun document.location 26

27. wsj.com/search? searchUrl = wsj.com/search? ; doSearch = function(s) { var u = searchUrl + s; document.location = u; } doSearch(SearchBox.value); searchUrl /* a.com/ad1.js */ displayAd = function() { ... }; displayAd(); u s Fun Fun doSearch displayAd SearchBox.value Fun Fun document.location 27

28. wsj.com/search? searchUrl = wsj.com/search? ; doSearch = function(s) { var u = searchUrl + s; document.location = u; } searchUrl = wsj.com/search? ; doSearch = function(s) { var u = searchUrl + s; document.location = u; } doSearch(SearchBox.value); doSearch(SearchBox.value); searchUrl /* a.com/ad1.js */ displayAd = function() { ... }; displayAd(); u s Fun Fun doSearch displayAd SearchBox.value Fun Fun document.location 28

29. wsj.com/search? searchUrl = wsj.com/search? ; doSearch = function(s) { var u = searchUrl + s; document.location = u; } searchUrl = wsj.com/search? ; doSearch = function(s) { var u = searchUrl + s; document.location = u; } doSearch(SearchBox.value); doSearch(SearchBox.value); searchUrl evil.com/ /* a.com/ad2.js */ searchUrl = evil.com ; u s Fun doSearch SearchBox.value Fun document.location 29

30. wsj.com/search? searchUrl = wsj.com/search? ; doSearch = function(s) { var u = searchUrl + s; document.location = u; } searchUrl = wsj.com/search? ; doSearch = function(s) { var u = searchUrl + s; document.location = u; } doSearch(SearchBox.value); doSearch(SearchBox.value); searchUrl evil.com/ /* a.com/ad2.js */ searchUrl = evil.com ; u s Fun doSearch SearchBox.value Fun document.location 30

31. wsj.com/search? searchUrl = wsj.com/search? ; doSearch = function(s) { var u = searchUrl + s; document.location = u; } searchUrl = wsj.com/search? ; doSearch = function(s) { var u = searchUrl + s; document.location = u; } doSearch(SearchBox.value); doSearch(SearchBox.value); searchUrl /* a.com/ad3.js */ doSearch( foo ); u s Fun doSearch foo Fun SearchBox.value Fun document.location 31

32. wsj.com/search? searchUrl = wsj.com/search? ; doSearch = function(s) { var u = searchUrl + s; document.location = u; } doSearch(SearchBox.value); searchUrl /* a.com/ad3.js */ doSearch( foo ); u s Fun doSearch foo Fun SearchBox.value Fun document.location 32

33. Outline Overview JavaScript Static Analysis Computing Residual Policies Additional Challenges Evaluation 33

34. wsj.com/search? searchUrl = wsj.com/search? ; doSearch = function(s) { var u = searchUrl + s; document.location = u; } doSearch(SearchBox.value); Add taint to sensitive data and propagate searchUrl searchUrl No Write u u document.location s s Fun Fun searchUrl doSearch doSearch SearchBox.value No Read SearchBox.value SearchBox.value Fun doSearch document.location document.location 34

35. Residual Policies Difficulties: Aliasing First-class functions Don t want flow analysis in browser Solution: Conservatively taint functions Conservatively taint fields 35

36. No Write Taint Tainted Functions No Read Taint Transfer taints from parameters to functions Fun Fun No Write to No Read foo foo // hole redefines foo foo = function(t) { // reads t, hence cookie } No Read to No Write foo foo Fun Fun foo(document.cookie); Transfer taints from return values to functions 36

37. Aliasing and Tainted Fields No Write tmp = document; No Read z = tmp.cookie; document.cookie // reads z tmp.cookie z Residual policy misses future aliasing Conservative approach: if field f is tainted for some object, f tainted for all 37

38. Outline Overview JavaScript Static Analysis Computing Residual Policies Additional Challenges Evaluation 38

39. Objects Used pervasively in JavaScript Hence, analysis must be field-sensitive Encode setter and getter for field f using Fldf x = { f:1 }; x.g = 2; Fields can be dynamically added Initially assume no fields Iteratively add constraints until fixpoint 39

40. Prototypes JavaScript uses prototype-based inheritance Intuitively, each object x has a link to its parent inherits parent s fields x.parent x Ensures each object has fields of its ancestors 40

41. Indirect Flows if (document.cookie == foo ) { y = 1; } INDIRECT document.cookie y 1 Propagate taints along indirect flow edges But not program values 41

42. Outline Overview JavaScript Static Analysis Computing Residual Policies Additional Challenges Evaluation 42

43. Implementation Flow analysis and residual policy generator parse JavaScript (JSure) generate set constraints (6,000 lines of OCaml) solve constraints (Banshee + 400 lines of C) Stand-alone residual policy checker not yet incorporated into browser JavaScript collector Firefox extension (500 lines of JavaScript) 43

44. Experimental Setup Collect JavaScript for Alexa top 100 web sites server code Context: all server code Hole: all third-party code third-party code 97/100 have JavaScript 63/97 have holes 44

45. Experimental Setup Information flow analysis on context + hole cookie confidentiality / location integrity Compute residual policy, check it on hole / 45

46. Scalability of Full Analysis 90 80 70 Running time (seconds) 60 Average: 9.9 sec 50 80% run in <12 sec 40 30 20 10 0 0 5 10 15 Lines of code (thousands) 20 25 30 35 40 45 46

47. Average Running Times Full Analysis / 9.9 sec Staged Analysis / 14.0 sec 0.13 sec 47

48. Results of Analysis: Full 30 32 Hole satisfies cookie policy? 30 32 48

49. Results of Analysis: Staged 30 32 Hole satisfies cookie policy? Residual checker: 26 32 26/30 safe Imprecision: 4 false positives 4 49

50. Future Work Context-sensitivity Dynamically-constructed field names Test more complicated policies Embed residual policy checker in browser 50

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