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Integrity protection for 3rd-party JavaScript François Marier @fmarier mozilla

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Firefox Security & Privacy

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Web Platform

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Web Platform

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Content Security Policy aka CSP

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Content Security Policy aka CSP mechanism for preventing XSS

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telling the browser what external content is allowed to load

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what does CSP look like?

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$ curl --head https://mega.nz HTTP/1.1 200 OK Content-Type: text/html Content-Length: 1989 Content-Security-Policy: default-src 'self' *.mega.co.nz *.mega.nz http://*.mega.co.nz http://*.mega.nz; script-src 'self' mega.co.nz mega.nz data: blob:; style-src 'self' 'unsafe-inline' *.mega.nz *.mega.co.nz data: blob:; frame-src 'self' mega:; img-src 'self' *.mega.co.nz *.mega.nz data:

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Hi you alert('p0wned'); ! Tweet! What's on your mind?

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without CSP

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Hi you! John Doe - just moments ago p0wned Ok

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with CSP

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Hi you! John Doe - just moments ago

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Content-Security-Policy: script-src 'self' https://cdn.example.com

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inline scripts are blocked unless unsafe-inline is specified

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script-src object-src style-src img-src media-src frame-src font-src connect-src

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$ curl --head https://twitter.com HTTP/1.1 200 OK content-length: 58347 content-security-policy: … report-uri https://twitter.com/csp_report violation reports:

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"csp-report": { "document-uri": "http://example.org/page.html", "referrer": "http://evil.example.com/haxor.html", "blocked-uri": "http://evil.example.com/image.png", "violated-directive": "default-src 'self'", "effective-directive": "img-src", "original-policy": "default-src 'self'; report-uri http://example.org/..." }

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support for inline scripts Content-Security-Policy: script-src 'sha256-YWIzOW...'

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Strict Transport Security aka HSTS

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Strict Transport Security aka HSTS mechanism for preventing HTTPS to HTTP downgrades

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telling the browser that your site should never be reached over HTTP

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GET bank.com.au 301 → GET https://bank.com.au 200 → no HSTS, no sslstrip

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GET bank.com.au → 200 no HSTS, with sslstrip

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what does HSTS look like?

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$ curl -i https://login.xero.com HTTP/1.1 200 OK Cache-Control: private Content-Type: text/html; charset=utf-8 Strict-Transport-Security: max-age=31536000 X-Frame-Options: SAMEORIGIN

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with HSTS, with sslstrip GET https://bank.com.au 200 →

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silent client-side redirects HTTP → HTTPS

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no HTTP traffic for sslstrip to tamper with

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except for the very first connection

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https://hstspreload.appspot.com/

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pop quiz! how many .au sites are on the preload list?

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aurainfosec.com.au bcm.com.au bigbrownpromotions.com.au comssa.org.au data.qld.gov.au dreamsforabetterworld.com.au dylanscott.com.au fatzebra.com.au freethought.org.au netrider.net.au publications.qld.gov.au technotonic.com.au thomastimepieces.com.au tracktivity.com.au tradingcentre.com.au webandwords.com.au 16

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aurainfosec.com.au bcm.com.au bigbrownpromotions.com.au comssa.org.au data.qld.gov.au dreamsforabetterworld.com.au dylanscott.com.au fatzebra.com.au freethought.org.au netrider.net.au publications.qld.gov.au technotonic.com.au thomastimepieces.com.au tracktivity.com.au tradingcentre.com.au webandwords.com.au

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2015?

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https://ajax.googleapis.com /ajax/libs/jquery/1.8.0/ jquery.min.js

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how common is this?

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what would happen if that server were compromised?

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Bad Things™ steal sessions leak confidential data redirect to phishing sites enlist DDoS zombies

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simple solution

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instead of this:

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do this:

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You owe me $10.00. f4243c12541be6f79c73e539c426e07a f2f6c4ef8794894f4903aee54542586d

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You owe me $1000. 1ebd7a8d15a6dab743f0c4d147f731bc fc6b74752afe43afa5389ba8830a2215

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guarantee: script won't change or it'll be blocked

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limitation: won't work for scripts that change all the time

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3 types of scripts

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dynamically-generated script: not a good fit for SRI I

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immutable scripts: perfect for SRI II

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https://ajax.googleapis.com /ajax/libs/jquery/1.8.0/ jquery.min.js

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what about your own scripts? (they change, but you're the one changing them)

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III scripts under your control: good fit for SRI

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can usually add the hashing to your static resource pipeline

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#!/bin/sh cat src/*.js > bundle.js HASH=`sha256sum bundle.js |cut -f1 -d' '` mv bundle.js public/bundle-${HASH}.js

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public/bundle-c2498bc358....js Cache-Control: max-age=∞

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<script src=”app.js”> <script src=”menu.js”>

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what else?

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integrity=” sha256-9Cm9ekBvKrtQ0A... “ sha256-rKSr3LcX+EkeM=... sha256-1z4uG/+cVbhShP... sha384-RqG7UC/QK2TVRa... sha512-AODL7idgffQeNs... ”

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integrity=” sha256-9Cm9ekBvKrtQ0A... sha256-rKSr3LcX+EkeM=... sha256-1z4uG/+cVbhShP... “ sha384-RqG7UC/QK2TVRa... sha512-AODL7idgffQeNs... ”

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integrity=” sha256-9Cm9ekBvKrtQ0A... sha256-rKSr3LcX+EkeM=... sha256-1z4uG/+cVbhShP... sha384-RqG7UC/QK2TVRa... sha512-AODL7idgffQeNs... ”

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what about cross-origin requests?

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“a web browser permits scripts contained in a first web page to access data in a second web page, but only if both web pages have the same origin” same-origin policy

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example.com/index.html

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example.com/index.html example.com/data.js: var secret = 42;

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example.com/index.html example.com/data.js: var secret = 42; evil.net/widget.js: exfiltrate(secret);

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example.com/index.html example.com/data.js: var secret = 42; evil.net/widget.js: exfiltrate(secret);

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on the server: Access-Control-Allow-Origin: *

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on the server: Access-Control-Allow-Origin: * on the client: crossorigin=”anonymous”

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complete example:

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complete example:

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cat file.js | openssl dgst -sha256 -binary | openssl enc -base64 -A

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SRIhash.org

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status?

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spec is being finalized

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(initial implementations)

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demo

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Bug 992096 - Implement SRI

This should be red if the hash matches!

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h1 { color: red; }

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Bug 992096 - Implement SRI

This should be red if the hash matches!

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Questions? feedback: [email protected] mozilla.dev.security [email protected] © 2015 François Marier This work is licensed under a Creative Commons Attribution-ShareAlike 4.0 License.

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photo credits: bank notes: https://www.flickr.com/photos/epsos/8463683689 web devs: https://www.flickr.com/photos/mbiddulph/238171366 explosion: https://www.flickr.com/photos/-cavin-/2313239884/