Securing PHP Web Applications Book

Acknowledgments xiii

About the Authors xv

Part I: Web Development Is a Blood Sport–Don't Wander onto the Field Without a Helmet 1

Chapter 1: Security Is a Server Issue and Other Myths 3

Reality Check 3

Security Is a Server Issue 5

Security Through Obscurity 7

Native Session Management Provides Plenty of Security 9

“My Application Isn’t Major Enough to Get Hacked” 9

The “Barbarians at the Gate” Syndrome 10

Wrapping It Up 10

Part II: Is That Hole Really Big Enough to Drive a Truck Through? 11

Chapter 2: Error Handling 13

The Guestbook Application 13

Users Do the Darnedest Things . . . 15

Building an Error-Handling Mechanism 19

Wrapping It Up 26

Chapter 3: System Calls 27

Navigating the Dangerous Waters of exec(), system(), and Backticks 27

Using escapeshellcmd() and escapeshellarg() to Secure System Calls 30

Create an API to Handle All System Calls 31

Patch the Guestbook Application 32

Wrapping It Up 34

Part III: What's In a Name? More Than You Expect 35

Chapter 4: Buffer Overflows and Variable Sanitation 37

What Is a Buffer, How Does It Overflow, and Why Should You Care? 37

Prevent Buffer Overflows by Sanitizing Variables 46

Patch the Application 49

Wrapping It Up 52

Chapter 5: Input Validation 53

New Feature: Allow Users to Sign Their Guestbook Comments 53

The Problem: Users Who Give You More Than You Asked For 54

Assumptions: You Know What Your Data Looks Like 55

The Solution: Regular Expressions to Validate Input 57

Wrapping It Up 67

Chapter 6: Filesystem Access: Accessing the Filesystem for Fun and Profit 69

Opening Files 69

Creating and Storing Files 73

Changing File Properties Safely 76

Patching the Application to Allow User-Uploaded Image Files 88

Wrapping It Up 90

Part IV: “Aw come on man, you can trust me” 93

Chapter 7: Authentication 95

What Is User Authentication? 95

Privileges 100

How to Authenticate Users 101

Storing Usernames and Passwords 115

Patching the Application to Authenticate Users 117

Wrapping It Up 120

Chapter 8: Encryption 121

What Is Encryption? 121

Choosing an Encryption Type 123

Password Security 125

Patching the Application to Encrypt Passwords 125

Wrapping It Up 128

Chapter 9: Session Security 129

What Is a Session Variable? 129

Major Types of Session Attacks 129

Patching the Application to Secure the Session 133

Wrapping It Up 136

Chapter 10: Cross-Site Scripting 137

What Is XSS? 137

Reflected XSS 137

Stored XSS 138

Patching the Application to Prevent XSS Attacks 138

Wrapping It Up 139

Part V: Locking Up for the Night 141

Chapter 11: Securing Apache and MySQL 143

Programming Languages, Web Servers, and Operating Systems Are Inherently Insecure 143

Securing a UNIX, Linux, or Mac OS X Environment 144

Securing Apache 147

Securing MySQL 159

Wrapping It Up 166

Chapter 12: Securing IIS and SQL Server 167

Securing a Windows Server Environment 167

Securing IIS 177

Securing SQL Server 187

Wrapping It Up 205

Chapter 13: Securing PHP on the Server 207

Using the Latest Version of PHP 207

Using the Security Features Built into PHP and Apache 213

Using ModSecurity 215

Hardening php.ini 216

Wrapping It Up 218

Chapter 14: Introduction to Automated Testing 219

Why Are We Talking About Testing in a Security Book? 219

Testing Framework 220

Types of Tests 222

Choosing Solid Test Data 223

Wrapping It Up 224

Chapter 15: Introduction to Exploit Testing 225

What Is Exploit Testing? 225

Fuzzing 226

Testing Toolkits 233

Proprietary Test Suites 246

Wrapping It Up 254

Part VI: “Don’t Get Hacked” Is Not a Viable Security Policy 255

Chapter 16: Plan A: Designing a Secure Application from the Beginning 257

Before You Sit Down at the Keyboard . . . 257

Identifying Points of Failure 269

Wrapping It Up 271

Chapter 17: Plan B: Plugging the Holes in Your Existing Application 273

Set Up Your Environment 273

Application Hardening Checklist 276

Wrapping It Up 278

Epilogue: Security Is a Lifestyle Choice: Becoming a Better Programmer 279

Avoid Feature Creep 279

Write Self-Documenting Code 280

Use the Right Tools for the Job 282

Have Your Code Peer-Reviewed 283

Wrapping It Up 284

Appendix: Additional Resources 285

PEAR 285

Books 286

Web Sites 287

Tools 288

Glossary 289

Index 293