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Ajax Security
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.
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 413
ASP.NET AJAX (formerly Atlas) 414
ScriptService 417
Security Showdown: UpdatePanel Versus ScriptService 419
ASP.NET AJAX and WSDL 420
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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