Web Application Security

Contents

ACKNOWLEDGMENTS

PART I Primer

1 Welcome to the Wide World of Web Application Security

Misplaced Priorities and the Need for a New Focus

Network Security versus Application Security: The Parable of the Wizard and the Magic Fruit Trees

Real-World Parallels

Thinking like a Defender

The OWASP Top Ten List

#2. Cross-Site Scripting (XSS)

#3. Broken Authentication and Session Management

#4. Insecure Direct Object References

#5. Cross-Site Request Forgery

#6. Security Misconfiguration

#7. Insecure Cryptographic Storage

#8. Failure to Restrict URL Access

#9. Insufficient Transport Layer Protection

#10. Unvalidated Redirects and Forwards

Wrapping Up the OWASP Top Ten

Secure Features, Not Just Security Features

2 Security Fundamentals

Input Validation

Blacklist Validation

Whitelist Validation

More Validation Practices

The Defense-in-Depth Approach

Attack Surface Reduction

Attack Surface Reduction Rules of Thumb

Classifying and Prioritizing Threats

Common Weakness Enumeration (CWE)

Common Vulnerability Scoring System (CVSS)

PART II Web Application Security Principles

3 Authentication

Access Control Overview

Authentication Fundamentals

Proving Your Identity

Two-Factor and Three-Factor Authentication

Web Application Authentication

Password-Based Authentication Systems

Built-In HTTP Authentication

Single Sign-On Authentication

Custom Authentication Systems

Validating Credentials

Securing Password-Based Authentication

Attacks Against Passwords

The Importance of Password Complexity

Password Best Practices

Secure Authentication Best Practices

When and Where to Perform Authentication

Securing Web Authentication Mechanisms

4 Authorization

Access Control Continued

Session Management

Authorization Fundamentals

Authorization Goals

Detailed Authorization Check Process

Types of Permissions

Authorization Layers

Controls by Layer

Custom Authorization Mechanisms

Client-Side Attack

TOCTTOU Exploit

Web Authorization Best Practices

Attacks Against Authorization

Session Management Fundamentals

What’s a Session?

How to Manage Session State?

Why Do We Need Session Management?

Attacks Against Sessions

Jetty: Session Predictability in the Real World

Attacks Against Session State

Securing Web Application Session Management

Session Management Best Practices

5 Browser Security Principles: The Same-Origin Policy

Defining the Same-Origin Policy

An Important Distinction: Client-Side vs. Server-Side

A World Without the Same-Origin Policy

Exceptions to the Same-Origin Policy

HTML <script> Element

iframes and JavaScript document.domain

Adobe Flash Player Cross-Domain Policy File

Microsoft Silverlight

XMLHttpRequest (Ajax) and Cross-Origin Resource Sharing

Final Thoughts on the Same-Origin Policy

6 Browser Security Principles: Cross-Site Scripting and Cross-Site Request Forgery

Cross-Site Scripting

Cross-Site Scripting Explained

POST-Based Reflected XSS

Another Variation: HTML Injection

XSS Defense: Encoding Output

XSS Defense: Sanitizing Input

XSS Defense: Using a Reduced Markup Language

XSS Defense-in-Depth: HttpOnly

XSS Defense-in-Depth: Content Security Policy (CSP)

Final Thoughts on Cross-Site Scripting

Cross-Site Request Forgery

Cross-Site Request Forgery Explained

HTTP GET and the Concept of Safe Methods

Ineffective CSRF Defense: Relying on POST

Ineffective CSRF Defense: Checking the Referer Header

Ineffective CSRF Defense: URL Rewriting

Better CSRF Defense: Shared Secrets

Better CSRF Defense: Double-Submitted Cookies

Reauthentication

What Being “Logged In” Means

Final Thoughts on Cross-Site Request Forgery

7 Database Security Principles

Structured Query Language (SQL) Injection

SQL Injection Effects and Confidentiality-Integrity-Availability

The Dangers of Detailed Errors

Blind SQL Injection: No Errors Required

Solving the Problem: Validating Input

Regular Expressions

Solving the Problem: Escaping Input

Setting Database Permissions

Single Account Security

Separate Accounts for Separate Roles

Stored Procedure Security

The Stored-Procedures-Only Approach: Reducing Permissions Even Further

SQL Injection in Stored Procedures

Insecure Direct Object References

No Technical Knowledge Required

Insecure Direct Object References and Confidentiality-Integrity-Availability

Solving the Problem: Pre- or Post-Request Authorization Checks

Final Thoughts on Insecure Direct Object References

8 File Security Principles

Keeping Your Source Code Secret

Static Content and Dynamic Content

Revealing Source Code

Interpreted versus Compiled Code

Backup File Leaks

Include-File Leaks

Keep Secrets Out of Static Files

Exposing Sensitive Functionality

Security Through Obscurity

Forceful Browsing

Forceful Browsing and Insecure Direct Object References

Directory Enumeration

Redirect Workflow Manipulation

Directory Traversal

More Directory Traversal Vulnerabilities

Canonicalization

PART III Secure Development and Deployment

9 Secure Development Methodologies

Baking Security In

The Earlier, the Better

The Penetrate-and-Patch Approach

The Holistic Approach to Application Security

Threat Modeling

Secure Coding Libraries

Security Testing

Security Incident Response Planning

Industry Standard Secure Development Methodologies and Maturity Models

The Microsoft Security Development Lifecycle (SDL)

OWASP Comprehensive Lightweight Application Security Process (CLASP)

The Software Assurance Maturity Model (SAMM)

The Building Security In Maturity Model (BSIMM)

Conclusions on Secure Development Methodologies and Maturity Models

Epilogue The Wizard, the Giant, and the Magic Fruit Trees: A Happy Ending