Towards a Post-XSS World - JSConf EU 2013

Cross-site scripting attacks are pervasive and dangerously exploitable threats to modern web applications, undermining the critical assumption that your app’s code is actually under your control. But you know that already; you’re likely playing whack-a-mole right now with one of the dozens of potential attack vectors your app exposes.

Happily, we’re this close to eradicating XSS with some new tools like Content Security Policy. Come spend a half-hour of your life learning how you can stop worrying about maliciously injected script. You’ll be glad you did!

Transcript

1. Towards a Post- XSS World Mike West https://mikewest.org G+: mkw.st/+ Twitter: @mikewest Slides: https://mkw.st/r/jsconfeu13
2. http://www.html5rocks.com/en/tutorials/security/content-security-policy/ https://mkw.st/r/csp
4. Content injection is scary.
5. scheme://host:port
6. <script> beAwesome(); </script> <script> beEvil(); </script>
7. <script> beAwesome(); </script> <!-- <p>Hello, {$name}!</p> --> <p>Hello, <script> beEvil(); </script>!</p>
8. <style> p { color: {{USER_COLOR}}; } </style> <p> Hello {{USER_NAME}}, view your <a href="{{USER_URL}}">Account</a>. </p> <script> var id = {{USER_ID}}; </script> <!-- DEBUG: {{INFO}} -->
9. https://www.owasp.org/index.php/XSS_Filter_Evasion_Cheat_Sheet goo.gl/XE0aW
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11. [][(![]+[])[+[[+[]]]]+([][[]]+[])[+[[!+[]+!+[]+!+[]+!+[]+!+[]]]]+(![]+[])[+[[!+[]+!+[]]]]+(!![]+[]) [+[[+[]]]]+(!![]+[])[+[[!+[]+!+[]+!+[]]]]+(!![]+[])[+[[+!+[]]]]][([][(![]+[])[+[[+[]]]]+([][[]]+[]) [+[[!+[]+!+[]+!+[]+!+[]+!+[]]]]+(![]+[])[+[[!+[]+!+[]]]]+(!![]+[])[+[[+[]]]]+(!![]+[])[+[[!+[]+!+[] +!+[]]]]+(!![]+[])[+[[+!+[]]]]]+[])[+[[!+[]+!+[]+!+[]]]]+([][(![]+[])[+[[+[]]]]+([][[]]+[])[+[[!+[] +!+[]+!+[]+!+[]+!+[]]]]+(![]+[])[+[[!+[]+!+[]]]]+(!![]+[])[+[[+[]]]]+(!![]+[])[+[[!+[]+!+[]+!+[]]]] +(!![]+[])[+[[+!+[]]]]]+[])[+[[!+[]+!+[]+!+[]+!+[]+!+[]+!+[]]]]+([][[]]+[])[+[[+!+[]]]]+(![]+[])[+ [[!+[]+!+[]+!+[]]]]+(!![]+[])[+[[+[]]]]+(!![]+[])[+[[+!+[]]]]+([][[]]+[])[+[[+[]]]]+([][(![]+[])[+ [[+[]]]]+([][[]]+[])[+[[!+[]+!+[]+!+[]+!+[]+!+[]]]]+(![]+[])[+[[!+[]+!+[]]]]+(!![]+[])[+[[+[]]]]+ (!![]+[])[+[[!+[]+!+[]+!+[]]]]+(!![]+[])[+[[+!+[]]]]]+[])[+[[!+[]+!+[]+!+[]]]]+(!![]+[])[+[[+[]]]]+ ([][(![]+[])[+[[+[]]]]+([][[]]+[])[+[[!+[]+!+[]+!+[]+!+[]+!+[]]]]+(![]+[])[+[[!+[]+!+[]]]]+(!![]+ [])[+[[+[]]]]+(!![]+[])[+[[!+[]+!+[]+!+[]]]]+(!![]+[])[+[[+!+[]]]]]+[])[+[[!+[]+!+[]+!+[]+!+[]+!+[] +!+[]]]]+(!![]+[])[+[[+!+[]]]]]((![]+[])[+[[+!+[]]]]+(![]+[])[+[[!+[]+!+[]]]]+(!![]+[])[+[[!+[]+!+ []+!+[]]]]+(!![]+[])[+[[+!+[]]]]+(!![]+[])[+[[+[]]]]+([][(![]+[])[+[[+[]]]]+([][[]]+[])[+[[!+[]+!+ []+!+[]+!+[]+!+[]]]]+(![]+[])[+[[!+[]+!+[]]]]+(!![]+[])[+[[+[]]]]+(!![]+[])[+[[!+[]+!+[]+!+[]]]]+ (!![]+[])[+[[+!+[]]]]]+[])[+[[+!+[]]]+[[!+[]+!+[]+!+[]+!+[]+!+[]]]]+[+!+[]]+([][(![]+[])[+[[+[]]]]+ ([][[]]+[])[+[[!+[]+!+[]+!+[]+!+[]+!+[]]]]+(![]+[])[+[[!+[]+!+[]]]]+(!![]+[])[+[[+[]]]]+(!![]+[])[+ [[!+[]+!+[]+!+[]]]]+(!![]+[])[+[[+!+[]]]]]+[])[+[[+!+[]]]+[[!+[]+!+[]+!+[]+!+[]+!+[]+!+[]]]])() alert(1);
12. "I discount the probability of perfection." -Alex Russell
13. "We are all idiots with deadlines." -Mike West
14. http://traumwerk.stanford.edu/philolog/2009/10/homers_odyssey_in_art_sirens_f.html
15. http://w3.org/TR/CSP11
17. Content-Security-Policy: default-src 'none'; style-src https://mikewestdotorg.hasacdn.net; frame-src https://www.youtube.com https://www.speakerdeck.com; script-src https://mikewestdotorg.hasacdn.net https://ssl.google-analytics.com; img-src 'self' https://mikewestdotorg.hasacdn.net https://ssl.google-analytics.com; font-src https://mikewestdotorg.hasacdn.net
18. Content-Security-Policy: default-src ...; script-src ...; object-src ...; style-src ...; img-src ...; media-src ...; frame-src ...; font-src ...; connect-src ...; sandbox ...; report-uri https://example.com/reporter.cgi
19. Content-Security-Policy-Report-Only: default-src https:; report-uri https://example.com/csp-violations { "csp-report": { "document-uri": "http://example.org/page.html", "referrer": "http://evil.example.com/haxor.html", "blocked-uri": "http://evil.example.com/img.png", "violated-directive": "default-src 'self'", "original-policy": "...", "source-file": "http://example.com/script.js", "line-number": 10, "column-number": 11, } }
20. https://twitter.com/rwaldron/status/371801007829041153
21. <script> function handleClick() { ... } </script> <button onclick="handleClick()">Click me!</button> <a href="javascript:handleClick()">Click me!</a>
22. <!-- index.html --> <script src="clickHandler.js"></script> <button class="clckr">Click me!</button> <a href="#" class="clckr">Click me!</a> <!-- clickHandler.js --> function handleClick() { ... } function init() { for (var e in document.querySelectorAll('.clckr')) e.addEventListener('click', handleClick); }
23. Content-Security-Policy: script-src 'nonce-afbvjn+afpo-j1qer'; <button class="clckr">Click me!</button> <a href="#" class="clckr">Click me!</a> <script nonce="oafbvjn+afpo-j1qer"> function handleClick() { ... } function init() { var e; for (e in document.querySelectorAll('.clckr')) e.addEventListener('click', handleClick); } </script>
24. `eval()` is evil?
25. http://www.html5rocks.com/en/tutorials/security/sandboxed-iframes/ goo.gl/WJjv10
26. http://www.html5rocks.com/en/tutorials/security/content-security-policy/ https://mkw.st/r/csp
27. http://lcamtuf.coredump.cx/postxss/
28. https://mkw.st/r/jsconfeu13 https://mkw.st/r/csp Danke! Mike West https://mikewest.org G+: mkw.st/+ Twitter: @mikewest