Web security: Securing Untrusted Web Content in Browsers

Web security: Securing untrusted web content at

browsers

Phu H. PhungUniversity of Illinois at Chicago

ACM Chicago Chapter seminarSeptember 10, 2014

Loyola University ChicagoComputer Science Department

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Web page is rendered at browsers

• Web pages contain JavaScript code, a scripting language run at browsers

• JavaScript can provide a lot of functionalities rich interactions

92% of all websites use JavaScript [w3techs.com]

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“88.45% of the Alexa top 10,000 web sites included at least one remote JavaScript

library”CCS’12

Web-based mobile applications

• HTML5 + JavaScript is a new trend for mobile developerso Cross-platform development,

“Write one run everywhere”

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Third-party JavaScript is everywhere

• Advertisementso Adhese ad network

• Social webo Facebook Connecto Google+o Twittero Feedsburner

• Trackingo Scorecardresearch

• Web Analyticso Yahoo! Web

Analyticso Google Analytics

• …

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Two basic composition techniques

• Iframe integration

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<html><body>…<iframe src=“http://3rdparty.com/frame.html”></iframe>…</body></html>

3rd party

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Two basic composition techniques

<html><body>…<script src=“http://3rdparty.com/script.js”></script>…</body></html>

3rd party

Script inclusion

Third-party JavaScript issues

• Third-party script inclusion run with the same privilege of the hosting page.

• Security issues:oMalicious third-party codeo Trusted third-party is compromised oConfidentiality, integrity, and other

security risks

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Difficult issues with JavaScript

• JavaScript is a powerful language, but the language design is bad for security, e.g.:o Dynamic scripts: document.write, eval, ...o Encapsulation leakageo ...

<script> document.write(‘<scr’);document.write(‘ipt> malic’);var i= 1;document.write(‘ious code; </sc’);document.write(‘ript>’);</script>

<script> malicious code; </script>

A lot of attacks were

launched in practice

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Samy attack on Myspace

• MySpace tries to filter out JavaScript code in user data

• BUT: The malicious code was injected in a “strange” way that escapes the filter

<div id=mycode style="BACKGROUND: url('java script:eval(document.all.mycode.expr)')" expr="var B=String.fromCharCode(34);………">

</div>

Another real world attack

• Million Browser Botnet (July 2013)

o Leverage Advertising Networks using JavaScript to launch Application-Level DDoS

o Paid on 2 ad networks for displaying treacherous advertisements on pages visited by hundreds of thousands of people

(Malicious code run automatically without user knowledge)

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Jeremiah Grossman & Matt JohansenWhiteHat SECURITY

A recent attack on Reuter homepage (June 2014)

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• Reuters website was compromised by the Syrian Electronic Armyo By code injection via a compromised third

party ad network.

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State-of-the-art

• Limit third-party code to safe subset of JavaScripto Facebook JS, ADSafe, ADSafety, ...

• Browser-based sandboxing solutionso ConScript, WebJail, Contego, ...

• Server-side transformations of scripts to be includedo Google Caja, BrowserShield, ...

No compatibility with existing scripts

Browser modifications imply short-term deployment issues

No direct script delivery to browserGreat runtime overhead

Our approachLightweight Self-Protecting

JavaScript

• A behavioral sandbox model for JavaScriptoUsing only JS libraries and wrappersoNo browser modification is required o The JS code is keep in originalo Easily dealing with dynamic features of

JavaScript

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API call interception

alert implementation

JavaScript execution environment(e.g. browsers)

Native implementations

code pointers User functions

alert(‘Hi!’) window.alert

alert wrapper(+policy code)

Attacker codealert = function(){...};

alert wrapper

unique

(enforced by SPJS)

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Deployment illustration

<html> <head> <script src=“selfprotectingJS.js"></script> <title>Self-protecting JavaScript </title> <meta content=…> <style>…</style> <script>…</script>  </head> <body> <script type="text/javascript"> (function() {..})(); </script>  </body></html>

Policy code and

enforcement code defined in a text file

The enforcement code can be

deployed anywhere: server side, proxy or browser plug-in, i.e.

no need for a modified browser

The orgininal

code is not syntactically modified

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66.03

0

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Self-Protecting BrowserShield

Slo

wd

ow

n (t

imes

)

Runtime overhead

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Effectiveness• Defend almost all of the known XSS attacker

vectorso 34 attack vectors over 38 successful attack

vectors

• Provide Security Policy Patterns to build realistic policies e.g. prevent the attack of Firesheep on Facebook

• Defend real-world exploitso phpBB 2.0.18 vulnerabilities – a stored XSS

attacko WebCal vulnerabilities –a reflected XSS attack

Lightweight Self-Protecting JavaScript

Lightweight Self-Protecting JavaScript

ASIACCS’09

Safe Wrappers and Sane Policies for Self-Protecting

JavaScriptAppSec Research ’10

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SPJS with Untrusted JavaScript

• No privilege distinguish between hosting code and external code

Self-Protecting JavaScript Code TRUSTED

UNTRUSTEDHosting

codeHosting

codeHosting

code

external code

external code

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Goals• Deploy SPJS in the context of untrusted JS

o Load and execute untrusted code without pre-processing the code

o No browser modification is required

• Enforce modular and fined-grained, stateful security policies for a piece of untrusted codeo Protect the hosting page from untrusted code

• Robust to potential flaws in security policieso Bad written policies might not break security

Two-tier Sandbox Architecture

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Sandbox running

untrusted code, defined in a separate

file e.g. `untrusted.js’

Sandbox running policy code, defined in a separate JS e.g. `policy.js’

Base-line API implementation,in e.g. `api.js’ file

JavaScript environme

nt, e.g. the DOM

The policy code can only access the base-line API and provided wrapper

functions (ensuring no leaks to global)

The untrusted code can only access objects returned by the outer sandbox

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Two-tier sandbox architecture

var api = loadAPI(…);

var outerSandbox = cajaVM.compileModule(policyCode);

var enforcedAPI = outerSandbox(api);

var innerSandbox = cajaVM.compileModule(untrustedCode);

innerSandbox(enforcedAPI);

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The architecture in multiple-principal untrusted code

Policy 2Policy 1

untrusted

Policy 3

untrusted

untrusted

Base-line API implementationin e.g. `api.js’ file

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Sandboxing untrusted code

• Use Secure ECMAScript (SES) library developed by Google Caja teamo Load a piece of code to execute within an

isolated environment• The code can only interact with the outside world via

provided APIs

var api = {...}; //constructingvar makeSandbox = cajaVM.compileModule(untrustedCodeSrc);var sandboxed = makeSandbox(api);

Isolation technique: The SES library

Object-capability environment• Scripts can accesso Objects they create themselveso Objects explicitly handed to them

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APIGlobal context

untrustedCode

sandbox

Isolation technique: The SES library

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Policy definition

• Base-line APIs implementationo Can enforce coarse-grained, generic policies, e.g.:

• Sanitize HTML• Ensure complete mediation

• Fine-grained policies for multiple untrusted JavaScript codeo Modular, principal-specific, e.g.: script1 is allowed to

read/write reg_A, script2 is allowed to read reg_A o Stafeful, e.g.: limit the number of popups to 3 o Cross-principal stateful policies, e.g: after script1

write to reg_A, disallow access from script2 to reg_A

Base-line APIs implementation

• Create a Virtual DOMo Intercepting wrapper around real DOMo Consult security policy on each operationo Use Harmony Proxies to generically intercept

property accesses on objects

• Virtual DOM implementation uses the Membrane Patterno Wrap any object passed from DOM to sandbox

(return values)o Unwrap any object passed from sandbox to DOM

(arguments)28

Deployment model

• Untrusted code is loaded into a string variableo Using server-side proxy + XMLHttpRequest (to

overcome same origin policy)o CORS/UMP headers set by the script provider

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<script src=“http://3rdparty.com/script.js”></script>

<script src=“ses.js”></script><script src=“api.js”></script><script src=“policy0.js”></script><script>var script = get(“http://3rdparty.com/script.js”);ses.execute(script,policy0);</script>

before

after

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Secure dynamic script evaluation

• Special handlers to intercept all methods that allow script tags to be addedo node.appendChild, node.insertBefore,

node.replaceChild, node.insertAftero document.write, …o Event handlers in HTML, e.g. <…onclick=“javascript:xyz(…)”>

1. Parse partial DOM tree/HTML2. Execute scripts in the sandbox

environment

Case studies• Single principal code

• Multiple-principal codeo Context-aware ads

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Two-tier Sandbox Architecture

A Two-tier Sandbox Architecture for

Untrusted JavaScript

JSTools’12 JSand: complete client-side sandboxing of

third-party JavaScript without browser

modificationsACSAC’12

A recent published workPhu H. Phung, Maliheh Monshizadeh, Meera Sridhar, Kevin W. Hamlen, and V.N. Venkatakrishnan. Between Worlds: Securing Mixed JavaScript/ActionScript Multi-party Web Content. IEEE Transactions on Dependable and Secure Computing (TDSC), forthcoming.

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Thank you!

[email protected]

Extra slides

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Wrapper example

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Different parsing techniques

• Via a sandboxed iframe1. Create sandbox iframe2. Set content via srcdoc attributeo More performanceo Parsed exactly as will be interpreted by

browsero Executed asynchronously

• (Alternative) Via a HTML parsing library in JavaScript

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Loading additional code in the sandbox

• Several use cases require external code to be executed in a previously set up sandboxo Loading API + glue codeoDynamic script loading

• Two new operations:o innerEval(code)o innerLoadScript(url)

Web security: Securing Untrusted Web Content in Browsers

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Transcript of Web security: Securing Untrusted Web Content in Browsers