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Ajax Security
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Ajax Security

4.0 2
by Billy Hoffman, Bryan Sullivan

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ISBN-10: 0321491939

ISBN-13: 9780321491930

Pub. Date: 12/20/2007

Publisher: Addison-Wesley

The Hands-On, Practical Guide to Preventing Ajax-Related Security Vulnerabilities

More and more Web sites are being rewritten as Ajax applications; even traditional desktop software is rapidly moving to the Web via Ajax. But, all too often, this transition is being made with reckless disregard for security. If Ajax applications aren’t


The Hands-On, Practical Guide to Preventing Ajax-Related Security Vulnerabilities

More and more Web sites are being rewritten as Ajax applications; even traditional desktop software is rapidly moving to the Web via Ajax. But, all too often, this transition is being made with reckless disregard for security. If Ajax applications aren’t designed and coded properly, they can be susceptible to far more dangerous security vulnerabilities than conventional Web or desktop software. Ajax developers desperately need guidance on securing their applications: knowledge that’s been virtually impossible to find, until now.

Ajax Security systematically debunks today’s most dangerous myths about Ajax security, illustrating key points with detailed case studies of actual exploited Ajax vulnerabilities, ranging from MySpace’s Samy worm to MacWorld’s conference code validator. Even more important, it delivers specific, up-to-the-minute recommendations for securing Ajax applications in each major Web programming language and environment, including .NET, Java, PHP, and even Ruby on Rails. You’ll learn how to:

· Mitigate unique risks associated with Ajax, including overly granular Web services, application control flow tampering, and manipulation of program logic

· Write new Ajax code more safely—and identify and fix flaws in existing code

· Prevent emerging Ajax-specific attacks, including JavaScript hijacking and persistent storage theft

· Avoid attacks based on XSS and SQL Injection—including a dangerous SQL Injection variant that can extract an entire backend database with just two requests

· Leverage security built into Ajax frameworks like Prototype, Dojo, and ASP.NET AJAX Extensions—and recognize what you still must implement on your own

· Create more secure “mashup” applications

Ajax Security will be an indispensable resource for developers coding or maintaining Ajax applications; architects and development managers planning or designing new Ajax software, and all software security professionals, from QA specialists to penetration testers.

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Table of Contents

Preface xvii

Preface (The Real One) xvix

Chapter 1 Introduction to Ajax Security 1

An Ajax Primer 2

What Is Ajax? 2

Asynchronous 3

JavaScript 6

XML 11

Dynamic HTML (DHTML) 11

The Ajax Architecture Shift 11

Thick-Client Architecture 12

Thin-Client Architecture 13

Ajax: The Goldilocks of Architecture 15

A Security Perspective: Thick-Client Applications 16

A Security Perspective: Thin-Client Applications 17

A Security Perspective: Ajax Applications 18

A Perfect Storm of Vulnerabilities 19

Increased Complexity, Transparency, and Size 19

Sociological Issues 22

Ajax Applications: Attractive and Strategic Targets 23

Conclusions 24

Chapter 2 The Heist 25

Eve 25

Hacking HighTechVacations.net 26

Hacking the Coupon System 26

Attacking Client-Side Data Binding 32

Attacking the Ajax API 36

A Theft in the Night 42

Chapter 3 Web Attacks 45

The Basic Attack Categories 45

Resource Enumeration 46

Parameter Manipulation 50

Other Attacks 75

Cross-Site Request Forgery (CSRF) 75

Phishing 76

Denial-of-Service (DoS) 77

Protecting Web Applications from Resource Enumeration and Parameter

Manipulation 77

Secure Sockets Layer 78

Conclusions 78

Chapter 4 Ajax Attack Surface 81

Understanding the Attack Surface 81

Traditional Web Application Attack Surface 83

Form Inputs 83

Cookies 84

Headers 85

Hidden Form Inputs 86

Query Parameters 86

Uploaded Files 89

Traditional Web Application Attacks: A Report Card 90

Web Service Attack Surface 92

Web Service Methods 92

Web Service Definitions 94

Ajax Application Attack Surface 94

The Origin of the Ajax Application Attack Surface 96

Best of Both Worlds–for the Hacker 98

Proper Input Validation 98

The Problem with Blacklisting and Other Specific Fixes 99

Treating the Symptoms Instead of the Disease 102

Whitelist Input Validation 105

Regular Expressions 109

Additional Thoughts on Input Validation 109

Validating Rich User Input 111

Validating Markup Languages 111

Validating Binary Files 113

Validating JavaScript Source Code 114

Validating Serialized Data 120

The Myth of User-Supplied Content 122

Conclusion 123

Chapter 5 Ajax Code Complexity 125

Multiple Languages and Architectures 125

Array Indexing 126

String Operations 128

Code Comments 129

Someone Else’s Problem 130

JavaScript Quirks 132

Interpreted, Not Compiled 132

Weakly Typed 133

Asynchronicity 135

Race Conditions 135

Deadlocks and the Dining Philosophers Problem 139

Client-Side Synchronization 144

Be Careful Whose Advice You Take 144

Conclusions 145

Chapter 6 Transparency in Ajax Applications 147

Black Boxes Versus White Boxes 147

Example: MyLocalWeatherForecast.com 150

Example: MyLocalWeatherForecast.com “Ajaxified” 152

Comparison Conclusions 156

The Web Application as an API 156

Data Types and Method Signatures 158

Specific Security Mistakes 158

Improper Authorization 159

Overly Granular Server API 161

Session State Stored in JavaScript 164

Sensitive Data Revealed to Users 165

Comments and Documentation Included in Client-Side Code 166

Data Transformation Performed on the Client 167

Security through Obscurity 172

Obfuscation 173

Conclusions 174

Chapter 7 Hijacking Ajax Applications 175

Hijacking Ajax Frameworks 176

Accidental Function Clobbering 176

Function Clobbering for Fun and Profit 178

Hijacking On-Demand Ajax 184

Hijacking JSON APIs 190

Hijacking Object Literals 195

Root of JSON Hijacking 195

Defending Against JSON Hijacking 196

Conclusions 199

Chapter 8 Attacking Client-Side Storage 201

Overview of Client-Side Storage Systems 201

General Client-Side Storage Security 202

HTTP Cookies 204

Cookie Access Control Rules 206

Storage Capacity of HTTP Cookies 211

Lifetime of Cookies 215

Additional Cookie Storage Security Notes 216

Cookie Storage Summary 216

Flash Local Shared Objects 218

Flash Local Shared Objects Summary 225

DOM Storage 226

Session Storage 227

Global Storage 229

The Devilish Details of DOM Storage 231

DOM Storage Security 233

DOM Storage Summary 234

Internet Explorer userData 235

Security Summary 240

General Client-Side Storage Attacks and Defenses 240

Cross-Domain Attacks 241

Cross-Directory Attacks 242

Cross-Port Attacks 243

Conclusions 243

Chapter 9 Offline Ajax Applications 245

Offline Ajax Applications 245

Google Gears 247

Native Security Features and Shortcomings of Google Gears 248

Exploiting WorkerPool 251

LocalServer Data Disclosure and Poisoning 253

Directly Accessing the Google Gears Database 257

SQL Injection and Google Gears 258

How Dangerous Is Client-Side SQL Injection? 262

Dojo.Offline 264

Keeping the Key Safe 265

Keeping the Data Safe 266

Good Passwords Make for Good Keys 267

Client-Side Input Validation Becomes Relevant 268

Other Approaches to Offline Applications 270

Conclusions 270

Chapter 10 Request Origin Issues 273

Robots, Spiders, Browsers, and Other Creepy Crawlers 273

“Hello! My Name Is Firefox. I Enjoy Chunked Encoding, PDFs, and

Long Walks on the Beach.” 275

Request Origin Uncertainty and JavaScript 276

Ajax Requests from the Web Server’s Point of View 276

Yourself, or Someone Like You 280

Sending HTTP Requests with JavaScript 282

JavaScript HTTP Attacks in a Pre-Ajax World 284

Hunting Content with XMLHttpRequest 286

Combination XSS/XHR Attacks in Action 290

Defenses 292

Conclusions 294

Chapter 11 Web Mashups and Aggregators 295

Machine-Consumable Data on the Internet 296

Early 90’s: Dawn of the Human Web 296

Mid 90s: The Birth of the Machine Web 297

2000s: The Machine Web Matures 298

Publicly Available Web Services 299

Mashups: Frankenstein on the Web 301

ChicagoCrime.org 302

HousingMaps.com 303

Other Mashups 304

Constructing Mashups 304

Mashups and Ajax 306

Bridges, Proxies, and Gateways–Oh My! 308

Ajax Proxy Alternatives 309

Attacking Ajax Proxies 310

Et Tu, HousingMaps.com? 312

Input Validation in Mashups 314

Aggregate Sites 317

Degraded Security and Trust 324

Conclusions 327

Chapter 12 Attacking the Presentation Layer 329

A Pinch of Presentation Makes the Content Go Down 329

Attacking the Presentation Layer 333

Data Mining Cascading Style Sheets 334

Look and Feel Hacks 337

Advanced Look and Feel Hacks 341

Embedded Program Logic 345

Cascading Style Sheets Vectors 347

Modifying the Browser Cache 348

Preventing Presentation Layer Attacks 352

Conclusion 353

Chapter 13 JavaScript Worms 355

Overview of JavaScript Worms 355

Traditional Computer Viruses 356

JavaScript Worms 359

JavaScript Worm Construction 361

JavaScript Limitations 363

Propagating JavaScript Worms 364

JavaScript Worm Payloads 364

Putting It All Together 372

Case Study: Samy Worm 373

How It Worked 374

The Virus’ Payload 377

Conclusions About the Samy Worm 379

Case Study: Yamanner Worm (JS/Yamanner-A) 380

How It Worked 380

The Virus’ Payload 383

Conclusions About the Yamanner Worm 384

Lessons Learned from Real JavaScript Worms 387

Conclusions 389

Chapter 14 Testing Ajax Applications 391

Black Magic 391

Not Everyone Uses a Web Browser to Browse the Web 396

Catch-22 398

Security Testing Tools–or Why Real Life Is Not Like Hollywood 399

Site Cataloging 400

Vulnerability Detection 401

Analysis Tool: Sprajax 403

Analysis Tool: Paros Proxy 406

Analysis Tool: LAPSE (Lightweight Analysis for Program Security in Eclipse) 408

Analysis Tool:WebInspect™ 409

Additional Thoughts on Security Testing 411

Chapter 15 Analysis of Ajax Frameworks 413


ASP.NET AJAX (formerly Atlas) 414

ScriptService 417

Security Showdown: UpdatePanel Versus ScriptService 419


ValidateRequest 424

ViewStateUserKey 425

ASP.NET Configuration and Debugging 426

PHP 427

Sajax 427

Sajax and Cross-Site Request Forgery 430

Java EE 431

Direct Web Remoting (DWR) 432

JavaScript Frameworks 434

A Warning About Client-Side Code 435

Prototype 435

Conclusions 437

Appendix A Samy Source Code 439

Appendix B Source Code for Yamanner Worm 447

Index 453

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Ajax Security 4 out of 5 based on 0 ratings. 2 reviews.
Anonymous More than 1 year ago
webapplications More than 1 year ago
Covers well known (XSS, , SQL injection, CSRF) and more obscure CSS attacks including detailed descriptions of actual exploits.

If you are planning on (or already do) using Ajax read this before your site becomes a victim.