Preface

"If popular culture has taught us anything, it is that someday mankind must face and destroy the growing robot menace."

Daniel H. Wilson, How to Survive a Robot Uprising

The past several years have seen huge strides in computer security, particularly in the field of software vulnerabilities. It seems as though every stop at the bookstore introduces a new title on topics such as secure development or exploiting software.

Books that cover application security tend to do so from the perspective of software designers and developers and focus on techniques to prevent software vulnerabilities from occurring in applications. These techniques start with solid security design principles and threat modeling and carry all the way through to implementation best practices and defensive programming strategies. Although they serve as strong defensive foundations for application development, these resources tend to give little treatment to the nature of vulnerabilities; instead, they focus on how to avoid them. What's more, every development team can't start rebuilding a secure application from the ground up. Real people have to deal with huge existing codebases, in-place applications, and limited time and budget. Meanwhile, the secure coding mantra seems to be "If it smells bad, throw it out." That's certainly necessary in some cases, but often it's too expensive and time consuming to be reasonable. So you might turn your attention to penetration testing and ethical hacking instead. A wide range of information on this topic is available, and it's certainly useful for the acid test of a software system. However, even the most technically detailed resources have a strong focus on exploit development and little to no treatment on how to find vulnerabilities in the first place. This still leaves the hanging question of how to find issues in an existing application and how to get a reasonable degree of assurance that a piece of software is safe.

This problem is exactly the one faced by those in the field of professional software security assessment. People are growing more concerned with building and testing secure systems, but very few resources address the practice of finding vulnerabilities. After all, this process requires a deep technical understanding of some very complex issues and must include a systematic approach to analyzing an application. Without formally addressing how to find vulnerabilities, the software security industry has no way of establishing the quality of a software security assessment or training the next generation in the craft. We have written this book in the hope of answering these questions and to help bridge the gap between secure software development and practical post-implementation reviews. Although this book is aimed primarily at consultants and other security professionals, much of the material will have value to the rest of the IT community as well. Developers can gain insight into the subtleties and nuances of how languages and operating systems work and how those features can introduce vulnerabilities into an application that otherwise appears secure. Quality assurance (QA) personnel can use some of the guidelines in this book to ensure the integrity of in-house software and cut down on the likelihood of their applications being stung by a major vulnerability. Administrators can find helpful guidelines for evaluating the security impact of applications on their networks and use this knowledge to make better decisions about future deployments. Finally, hobbyists who are simply interested in learning more about how to assess applications will find this book an invaluable resource (we hope!) for getting started in application security review or advancing their current skill sets.

Prerequisites

The majority of this book has been targeted at a level that any moderately experienced developer should find approachable. This means you need to be fairly comfortable with at least one programming language, and ideally, you should be familiar with basic C/C++ programming. At several stages throughout the book, we use Intel assembly examples, but we have attempted to keep them to a minimum and translate them into approximate C code when possible. We have also put a lot of effort into making the material as platform neutral as possible, although we do cover platform specifics for the most common operating systems. When necessary, we have tried to include references to additional resources that provide background for material that can't be covered adequately in this book.

How to Use This Book

Before we discuss the use of this book, we need to introduce its basic structure. The book is divided into three different parts:

• Part I: Introduction to Software Security Assessment (Chapters 14) These chapters introduce the practice of code auditing and explain how it fits into the software development process. You learn about the function of design review, threat modeling, and operational reviewtools that are useful for evaluating an application as a whole, and not just the code. Finally, you learn some generic high-level methods for performing a code review on any application, regardless of its function or size.

• Part II: Software Vulnerabilities (Chapters 513) These chapters shift the focus of the book toward practical implementation review and address how to find specific vulnerabilities in an application's codebase. Major software vulnerability classes are described, and you learn how to discover high-risk security flaws in an application. Numerous real-world examples of security vulnerabilities are given to help you get a feel for what software bugs look like in real code.

• Part III: Software Vulnerabilities in Practice (Chapters 1418) The final portion of the book turns your attention toward practical uses of lessons learned from the earlier chapters. These chapters describe a number of common application classes and the types of bugs they tend to be vulnerable to. They also show you how to apply the technical knowledge gained from Part II to real-world applications. Specifically, you look at networking, firewalling technologies, and Web technologies. Each chapter in this section introduces the common frameworks and designs of each application class and identifies where flaws typically occur.

You'll get the most value if you read this book straight through at least once so that you can get a feel for the material. This approach is best because we have tried to use each section as an opportunity to highlight techniques and tools that help you in performing application assessments. In particular, you should pay attention to the sidebars and notes we use to sum up the more important concepts in a section.

Of course, busy schedules and impending deadlines can have a serious impact on your time. To that end, we want to lay out a few tracks of focus for different types of reviews. However, you should start with Part 1 (Chapters 14) because it establishes a foundation for the rest of the book. After that, you can branch out to the following chapters:

• UNIX track (Chapters 510, 13) This chapter track starts off by covering common software vulnerability classes, such as memory corruption, program control flow, and specially formatted data. Then UNIX-centered security problems that arise because of quirks in the various UNIX operating systems are addressed. Finally, this track ends with coverage of synchronization vulnerabilities common to most platforms.

• Windows track (Chapters 58, 1113) This track starts off similarly to the UNIX track, by covering platform-neutral security problems. Then two chapters specifically address Windows APIs and their related vulnerabilities. Finally, this track finishes with coverage of common synchronization vulnerabilities.

• Web track (Chapters 8, 13, 17, 18) Web auditing requires understanding common security vulnerabilities as well as Web-based frameworks and languages. This track discusses the common vulnerability classes that pertain to Web-based languages, and then finishes off with the Web-specific chapters. Although the UNIX and Windows chapters aren't listed here, reading them might be necessary depending on the Web application's deployment environment.

• Network application track (Chapters 58, 13, 16) This sequence of chapters best addresses the types of vulnerabilities you're likely to encounter with network client/server applications. Notice that even though Chapter 16 is targeted at selected application protocols, it has a section for generic application protocol auditing methods. Like the previous track, UNIX or Windows chapters might also be relevant, depending on the deployment environment.

• Network analysis track (Chapters 58, 1316) This track is aimed at analyzing network analysis applications, such as firewalls, IPSs, sniffers, routing software, and so on. Coverage includes standard vulnerability classes along with popular network-based technologies and the common vulnerabilities in these products. Again, the UNIX and Windows chapters would be a good addition to this track, if applicable.