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Csp july2015
This document discusses Content Security Policy (CSP), which defines an HTTP header to whitelist approved sources of content like scripts to prevent XSS attacks. It describes how CSP directives like script-src restrict where code can be loaded from to enhance security. The speaker then demonstrates how to construct CSP policies and explains options like 'unsafe-inline' that disable the protection CSP is meant to provide. In the end, resources on CSP that informed the presentation are listed.
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Csp july2015
- 1. Content Security Policy OR HOWTO MAKE DEVELOPERS EVEN MORE LAZIER RIYAZ WALIKAR
- 2. whoami Security evangelist Do not work at a Big 4 One of the 3 OWASP Bangalore chapter leaders Extremely talkative
- 3. Same Origin Policy So you own http://banana.com Code from http://potato.com should not be able to access data from http://banana.com Browser’s sandbox and Origin protection XSS to bypass SOP
- 4. For the loveof XSS Reflected, Stored, DOM based
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- 7. The core issueexploited by XSS attacks is the browser’s inability to distinguish between script that’s intended to be part of your application, and script that’s been maliciously injected by a third-party. http://www.html5rocks.com/en/tutorials/security/content-security-policy/
- 8. I had youat Header Content Security Policy (CSP) defines the Content-Security-Policy HTTP header Whitelist script sources of trusted content Even if vulnerable to XSS, injected script will not trigger due to header definition
- 9. Building the policy So you trust scripts only from http://banana.com and your own domain (non inline) Content-Security-Policy: script-src 'self' http://banana.com So you want to load images only from http://potato.com and flash content from your own domain. Also, absolutely no scripts. Content-Security-Policy: script-src 'none'; img-src http://potato.com; object-src 'self'
- 10. CSP Directives default-src script-src style-src img-src connect-src font-src object-src media-src child-src sandbox report-uri The default-src is the default policy for loading content such as JavaScript, Images, CSS, fonts, AJAX requests, Frames and HTML5 Media Defines valid sources of JavaScript Defines valid sources of css (stylesheets) Defines valid sources of images Defines sources to which XMLHTTPRequest (AJAX), WebSocket or EventSource can fetch data from Defines valid sources of fontsDefines valid sources of plugins (for example: flash, embed tag, applet etc.) Defines valid source of audio and video Defines valid source for workers and embedded frame contents. frame-src is deprecated. child-src should be used. More about this laterInstructs the browser to POST a reports of policy failures to a specified URI.
- 11. CSP Source Declarations SourceValue Meaning * Wildcard, allows all origins. 'self' Allow same origin (current origin). 'none' Don't allow any resources of this directive to load. domain.example.com Allow a domain (explicit declaration) *.example.com Allow all subdomains on a domain. Exclude TLD. https://example.com Exact match including protocol https: Load from any domain but https data: Allow data uri (eg: Base64 encoded image)
- 12. unsafe-inline When script-srcor style-src are declared, inline script tags and css are disabled You can specify 'unsafe-inline' to execute inline script but that is precisely what CSP was designed to prevent!
- 13. unsafe-eval CSP disablesthe JavaScript function eval() by design To enable this explicitly, add 'unsafe-eval' to a script-src directive Not advised!
- 14. sandbox If present,browser treats the page as if it loaded inside an iframe with a sandbox attribute The browser severely restricts the page’s functionality, disabling JS, form submissions, plugins and objects You can keep the sandbox value empty to keep all restrictions in place, or add values: allow-forms allow-same-origin allow-scripts, and allow-top-navigation
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- 17. CSP 2.0! Severalnew enhancements including support for inline scripts in combination with a cryptographic nonce or hash sharing of the script itself Content-Security-Policy: script-src 'nonce-AY778asa229b2DEADBEEF' http://www.w3.org/TR/CSP2/
- 18. I read thefollowing to make this presentation http://www.w3.org/TR/2012/CR-CSP-20121115/ http://www.html5rocks.com/en/tutorials/security/content-security- policy/ http://content-security-policy.com/ http://caniuse.com/#feat=contentsecuritypolicy https://html.spec.whatwg.org/multipage/browsers.html#sandboxin g-flag-set http://www.w3.org/TR/CSP2/
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