Practical UNIX and Internet Security, 3rd Edition

Role of This Book

If we can’t change Unix and the environment in which it runs, the next best thing is to learn how to protect the system as best we can. That’s the goal of this book. If we can provide information to users and administrators in a way that helps them understand the way things work, and how they can use safeguards within the Unix environment, then we should be moving in the right direction. After all, these areas seem to be where many of the problems originate.

Unfortunately, knowing how things work on the system is not enough. Because of the Unix design, a single flaw in a Unix system program can compromise the security of the operating system as a whole. This is why vigilance and attention are needed to keep a system running securely: after a hole is discovered, it must be fixed. Furthermore, in this age of networked computing, that fix must be made widely available, lest some users who have not updated their software fall victim to more up-to-date attackers.

Tip

Although this book includes numerous examples of past security holes in the Unix operating system, we have intentionally not provided the reader with an exhaustive list of the means by which a machine can be penetrated. Not only would such information not necessarily help to improve the security of your system, but it might place a number of systems running older versions of Unix at additional risk.

Be aware that even properly configured Unix systems are still very susceptible to denial of service attacks, ...