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This chapter is from the book

Know Your Enemy: Common Software Security Pitfalls

There are many excellent software developers and architects in the world building all sorts of exciting things. The problem is that although these developers and architects are world class, they have not had the opportunity to learn much about security. Part of the issue is that most security courses at universities emphasize network security (that is, if the university teaches anything about security at all). Very little attention is paid to building secure software. Another part of the problem is that although some information exists covering software security, a comprehensive, practical guide to the topic has never really been available. We hope to change all that with this book.

The aphorism "Keep your friends close and your enemies closer" applies quite aptly to software security. Software security is really risk management. The key to an effective risk assessment is expert knowledge of security. Being able to recognize situations in which common attacks can be launched is half the battle. The first step in any analysis is recognizing the risks.

Software security risks come in two main flavors: architectural problems and implementation errors. We'll cover both kinds of security problems and their associated exploits throughout the book. Most software security material focuses on the implementation errors leading to problems such as buffer overflows (Chapter 7), race conditions (Chapter 9), randomness problems (Chapter 10), and a handful of other common mistakes. These issues are important, and we devote plenty of space to them.

But there is more to software security than avoiding the all-too-pervasive buffer overflow. Building secure software is like building a house. The kinds of bricks you use are important. But even more important (if you want to keep bad things out) is having four walls and a roof in the design. The same thing goes for software: The system calls that you use and how you use them are important, but overall design properties often count for more. We devote the first part of this book to issues that primarily apply at design time, including integrating security into your software engineering methodology, general principles for developing secure software systems, and dealing with security when performing security assessments.

It is important to understand what kinds of threats your software will face. At a high level, the answer is more or less any threat you can imagine from the real world. Theft, fraud, break-ins, and vandalism are all alive and well on the Internet.

Getting a bit more specific, we should mention a few of the more important types of threats of which you should be wary. One significant category of high-level threat is the compromise of information as it passes through or resides on each node in a network. Client/server models are commonly encountered in today's software systems, but things can get arbitrarily more complex. The kinds of attacks that are possible at each node are virtually limitless. We spend much of the book discussing different kinds of attacks. The attacks that can be launched vary, depending on the degree to which we trust the people at each node on the network.

One important kind of problem that isn't necessarily a software problem per se is social engineering, which involves talking someone into giving up important information, leading to the compromise of a system through pure charisma and chutzpah. Attackers often get passwords changed on arbitrary accounts just by calling up technical support, sounding angry, and knowing some easily obtained (usually public) information. See Ira Winkler's book Corporate Espionage for more information on social engineering [Winkler, 1997].

On the server side of software security, many threats boil down to malicious input problems. Chapter 12 is devoted to this problem. Buffer overflows (discussed in Chapter 7) are probably the most famous sort of malicious input problem.

Besides worrying about the nodes in a data communication topology, we have to worry about data being compromised on the actual communication medium itself. Although some people assume that such attacks aren't possible (perhaps because they don't know how to perform them), network-based attacks actually turn out to be relatively easy in practice. Some of the most notable and easiest to perform network attacks include

  • Eavesdropping. The attacker watches data as they traverse a network. Such attacks are sometimes possible even when strong cryptography is used. See the discussion on "man-in-the-middle" attacks in Appendix A.

  • Tampering. The attacker maliciously modifies data that are in transit on a network.

  • Spoofing. The attacker generates phony network data to give the illusion that valid data are arriving, when in reality the data are bogus.

  • Hijacking. The attacker replaces a stream of data on a network with his or her own stream of data. For example, once someone has authenticated a remote connection using TELNET, an attacker can take over the connection by killing packets from the client, and submitting "attack" packets. Such attacks generally involve spoofing.

  • Capture/replay. An attacker records a stream of data, and later sends the exact same traffic in an attempt to repeat the effects, with undesirable consequences. For example, an attacker may capture a transaction in which someone sells 100 shares of Microsoft stock. If the victim had thousands more, an attacker could wait for the stock price to dip, then replay the sale ad nauseam until the target had none remaining.

Cryptography can be used to solve these network problems to a varying degree. For those without exposure to cryptography basics, we provide an overview in Appendix A. In Chapter 11, we look at the practical side of using cryptography in applications.

Our simple list of threats is by no means comprehensive. What we present are some of the most important and salient concepts we want to expose you to up front. We discuss each of these threats, and many more, in detail throughout the book.

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