A CDN that can not XSS you. Using Subresource Integrity

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Peregrine Wilkins
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1 A CDN that can not XSS you Using Subresource Integrity

2 about:frederik Frederik Braun Security Engineer at Mozilla

3 Why am I here?

4 Content Delivery Networks

5 Who has seen code like this? <script src=" <link href=' ' rel='stylesheet' type='text/css'>

6 What does it do? <script src="

7 The Same-Origin Policy

8 Origins Explained :80

9 Can execute but most not read? <script src="

10 The Same Origin Policy

11 The Same Origin Policy XMLHttpRequest DOM Access Cookies Permissions

12 kotowicz's XSS-Track

13 kotowicz's XSS-Track

14 one vulnerability is enough

16 Picture from Cloudfare Popular JS libraries used for DDoS

17 Dear burglar, here's the combination to our safe. Please do not wake us up.

18 Subresource Integrity to the Rescue

20 SR I1.0 <script src=" integrity="sha256-c6cb9uyis9ujeqinphwthvqh/e1uhg5twh+y5qfqmyg=" crossorigin="anonymous"></script>

21 <script src=" integrity="sha256-c6cb9uyis9ujeqinphwthvqh/e1uhg5twh+y5qfqmyg=" SR I1.0 crossorigin="anonymous"></script>

22 Integrity Cryptographic Hash Functions

23 $ sha256sum ubuntu desktop-amd64.iso b970b014b3a2ea216fcf077328bfe32 18ed5c2f923fe2d9dfd2b41df9d735a5

24 Cryptographic Hash Functions Input Digest Fox cryptographic hash function DFCD 3454 BBEA 788A 751A 696C 24D CA99 2D17 The red fox jumps over the blue dog cryptographic hash function BB FB7D CBE2 823C ACC7 6CD1 90B1 EE6E 3ABC The red fox jumps ouer the blue dog cryptographic hash function 8FD F32 D1C6 76B1 79A9 0DA4 AEFE 4819 The red fox jumps oevr the blue dog cryptographic hash function FCD3 7FDB 5AF2 C6FF 915F D401 C0A9 7D9A 46AF FB45 The red fox jumps oer the blue dog cryptographic hash function 8ACA D682 D588 4C75 4BF D88 BCF8 92B9 6A6C Image released into the public domain by Wikipedia user Lichtspiel

25 Cryptographic Hash Functions Input normal jquery modified jquery Digest cryptographic hash function DFCD 3454 BBEA 788A 751A 696C 24D CA99 2D17 cryptographic hash function BB FB7D CBE2 823C ACC7 6CD1 90B1 EE6E 3ABC

26 Reading Cross-Origin Data?

27 { 'status': 'authenticated, 'username': 'Alice' }

28 Let's attack! <script src=" integrity="{ hash for Bob }"></script> <script src=" integrity="{ hash for Alice }"></script>

29 HTTP/ OK Accept-Ranges: bytes Cache-Control: max-age= Content-Type: text/html Date: Wed, 29 Apr :33:56 GMT Etag: " " Server: Content-Length: {'wifi_enabled': true,, 'password': 'admin'}

30 Cross Origin Resource Sharing (CORS)

31 Recap

32 CORS Required

33 Using CORS HTTP/ OK Accept-Ranges: bytes Cache-Control: max-age= Content-Type: text/html Date: Wed, 29 Apr :33:56 GMT Etag: " " Server: Access-Control-Allow-Origin: * Content-Length:

34 SR I1.0 <script src=" integrity="sha256-c6cb9uyis9ujeqinphwthvqh/e1uhg5twh+y5qfqmyg=" crossorigin="anonymous"></script>

35 The Fineprint

36 integrity Syntax SR I1.0 <script src=" integrity="sha256-c6cb9u qfqmyg=" crossorigin="anonymous"></script>

37 integrity Syntax SR I1.0 sha256-c6cb9u qfqmyg=

38 Multiple Hash Functions SR I1.0 <script src=" integrity="sha256-c6cb9u qfqmyg= sha384-h8brh8j48o9oyatfu5azz t1flm52t+ex6xo" crossorigin="anonymous"></script>

39 Multiple Hashes SR I1.0 <script src=" integrity="sha256-c6cb9uyis9ujeqinphwthvqh/e1uhg5twh+y5qfqmyg= sha256-qznlcsrox4gacp2dm0uckczcg+hiz1guq6zzdob/tng=" crossorigin="anonymous"></script>

40 Multiple Hashes SR I1.0 <script src=" integrity="sha256-c6cb9uyis9ujeqinphwth 5qFQmYg= sha256-qznlcsrox4gacp2dm0uck Dob/Tng= sha384-h8brh8j48o9oyatfu5azz t1flm52t+ex6xo sha384-vqh/e1uhg5twh+yczcg+h LznqHiZ1guq6ZZ" crossorigin="anonymous"></script>

41 Outdated Hash Function SR I1.0 <script src=" integrity="brokenalgo-c6cb9uyis9ujeqinphwh/e1uhg5twh+y5qfqmyg=" crossorigin="anonymous"></script>

42 over HTTP or HTTPS?

43 Failover

44 An evil script was blocked \o/

45 Manual Error Recovery <script src=" integrity="sha256-c6cb9uyis9ujeqinphwthvq " crossorigin="anonymous"></script> SR I1.0 <script>window.jquery document.write('<script src="/jquery-.min.js"><\/script>')</script>

46 Future Work

47 Built-in Error Recovery? NO T IN SP EC <script src=" integrity="sha256-c6cb9uyis9ujeqinphwthvq " crossorigin="anonymous" fallbacksrc="/jquery.min.js"> </script>

48 Integrity Policies & Error Reporting NO T IN SP EC Content-Security-Policy: integrity-policy: ("block" / "report" / "fallback") ["require-forall"]

49 More Use Cases SR I1.0 <link rel="stylesheet" href=" integrity="sha256-sdfwewfae wefjijfe"/>

50 NO T IN SP EC Integrity and videos

51 NO T IN SP EC Integrity and videos

52 We need your help!

53 Editor's Draft

54 Tool Support Needed

55 Enable CORS! Send Access-Control-Allow-Origin: * now!

56 Conclusion

57 You can soon add integrity to secure your script loads.

58 Extending the Web is non-trivial

59 Browser Security needs to step up (and will)

60 Frederik #security on irc.mozilla.org Obligatory Red Panda photo by Wikipedia user Aconcagua, CC-BY-SA-3.0 Thank you for listening!

Browser code isolation

CS 155 Spring 2016 Browser code isolation John Mitchell Acknowledgments: Lecture slides are from the Computer Security course taught by Dan Boneh and John Mitchell at Stanford University. When slides are