Malware: Fighting Malicious Code [Paperback]

Several years ago I attended a special conference on intrusion detection in McLean, Virginia. Each attendee was assigned to one of four teams charged with assessing the state of the art and making recommendations for future research in various areas related to intrusion detection. At the end, a representative from each team presented the output of that team's work to all attendees. Although each team's report was very interesting and worthwhile, the malicious code team's assessment of progress in that area particularly caught my attention. This team's conclusion was that not much genuine progress in characterizing and identifying malicious code had been made over the years. Given that viruses have been in existence for at least two decades and that all kinds of malicious code has been written and deployed "in the wild," it would not at all have been unexpected to hear that great strides in understanding malicious code have occurred to the point that sophisticated programs can now accurately and efficiently identify almost every instance of malicious code. But such was not the case. Some researchers who were not at the conference would undoubtedly disagree with the malicious code team's assessment, but I am confident that they would be in the minority. A considerable amount of work to better identify and deal with malware is underway, but genuine progress in understanding and detecting malware has indeed been frustratingly slow.

The irony of it all is that today's computing world is saturated with malware. Viruses and worms are so prevalent that newspaper, magazine, and television accounts of the "latest and greatest" virus or worm are now commonplace. Even young computer users typically understand basically what a virus is and why viruses are undesirable. "Create your own virus" toolkits have been available for years. Public "hacker tool" sites, relatively rare ten years ago, are now prevalent on the Internet. Going to a "hacker tool" site to obtain malware is not, however, necessary for someone to obtain malware. In August 2002, the Computer Emergency Response Team Coordination Center (CERT/CC) reported that a perpetrator had modified copies of the source code for OpenSSH such that they contained Trojan horse routines. Unsuspecting users went to the OpenSSH site and mirror sites to download OpenSSH in the expectation that they would be tightening security by encrypting network traffic between hosts. Instead, they introduced routines within the OpenSSH source that allowed attackers to gain remote control of their systems. And even Ed Skoudis, one of the few people in the world who can identify virtually every type of attack and also the author of this book, Malware: Fighting Malicious Code, reports in the first chapter that he found several Trojan horse programs that performed brute force password cracking in one of his systems. Malware is not a rarity; it is prevalent, and the problem is getting worse.

Malware does not exist in a vacuum--it cannot magically infuse itself into systems and network devices. Just as biological parasites generally exploit one or more weaknesses in the host, malware requires special conditions if it is to execute and then produce the intended results. Today's computing world, fortunately for the authors of malware but unfortunately for the user community, provides a nearly ideal environment. Why? Primarily, it is because of the many vulnerabilities in software that is commonly used today. Too many software vendors typically rush the software development process in an attempt to cut development costs and to get a competitive edge for their software products, thereby maximizing profits. The code they produce is often not carefully designed, implemented, or adequately tested. The result is bug-riddled software--software that behaves abnormally or, worse yet, causes the system on which it runs to behave abnormally, in many cases allowing perpetrators a chance to execute malware that exploits abnormal conditions and/or install more malware that does what perpetrators need it to do (such as capture keyboard output). With virtually no government regulation of the software industry and a user community that naively continues to purchase and use bug-riddled software and too often fails to patch the bugs that are discovered in it, malware truly has a "target rich" environment in which it can flourish.

Worse yet, a major change in the usability of cracking utilities has transpired. Not all that long ago, anyone who obtained a copy of a cracking utility usually had to struggle to learn how to use it. Most of the user interfaces were command line interfaces with a cryptic syntax that often only the author of a particular tool could master. Help facilities in these utilities was virtually unheard of. The result was difficult or impossible to use tools, tools that could be used by only "the few, the proud." The level of security-related threat was thus not really very high. The usability of cracking utilities has, however, improved substantially over time. A large number of tools are now so easy to use that they are often sarcastically called kiddie scripts. All a would-be attacker needs to do with such tools is download them, enter a little information (such as an answer to "What IP address do you want to attack?"), move a pointer to Go and then click a mouse button. The emergence of kiddie scripts has had much of the same effect that guns had centuries ago. Before guns were widely used in battle, a large individual, all things considered, had a huge advantage over a small individual. The gun became the "great equalizer." Kiddie scripts likewise are a great equalizer, although in a somewhat different sense. Someone who uses a kiddie script may not be able to do all the things that a very experienced attacker might be able to do, but the inexperienced person might at least be able to do many or most of these things.

The types of motivation to deploy malware are also eye opening. Traditional "hackers" are now only a part of the potential force of cyber world adversaries. Organized crime has moved into the computing arena, looking for opportunities such as making unauthorized funds transfers. Industrial espionage agents, disgruntled or greedy insiders, "information warfare" specialists within the military and government arenas, jilted lovers, sexual predators, identity thieves, and even cyber terrorists are among the many categories of individuals who are likely to use malware to breach security in systems and networks. Computer security professionals are taught that attacks are the by-products of capabilities, means, and opportunity. Malware translates to capabilities. The opportunities are truly mind-boggling when one considers just how diverse computing environments are today and how many different types of people can potentially obtain access to systems and networks.

All is not lost, however. The war against malware has at least a few bright sports. Anti-virus software is widely available today, for example, and, if it is updated regularly, it is effective in detecting and eradicating quite a few types of malware, especially (but not limited to) viruses and worms on Windows and Macintosh systems. The success of antivirus software represents some degree of victory in the war against malware. But the overwhelming majority of this type of software is pretty simplistic, as you'll see in Chapter 2 of this book, and, worse yet, there are many users who still do not run antivirus software on their Windows and Macintosh systems, or if they do, they may fail to update it as necessary. Other kinds of malware detection and eradication software have been developed, as covered in various chapters throughout this book, but once again the lack of deployment (often by organizations that need this type of software the most) is a major limitation with this type of software.

The problem of the existence of many types of malware and the fact that malware seems to become increasingly sophisticated so quickly has created a huge gap between malware as we know it and our capabilities of dealing with it. If we are ever going to reduce the size of this gap, we need to leap ahead instead of taking minute steps in understanding and dealing with malicious code. The availability of a detailed, comprehensive work on the types of malware that exist, how they work, and how to defend against them would be one of the best catalysts for such a leap. Malware: Fighting Malicious Code is such a work. Ed Skoudis presents the necessary groundwork for understanding malware in Chapter 1 with a neat little taxonomy, then proceeds to cover each major type of malicious code--viruses, worms, malicious mobile code, backdoors, Trojan horses, user-mode rootkits, kernel rootkits, and deeper levels of malicious code and hybrid malware, in the subsequent chapters. He then presents scenarios in which malicious code has been planted in systems and concludes with how to safely and effectively analyze potential and real malware. My favorite chapter is chapter eight (on kernel-mode rootkits) because Ed takes a topic in which there is at best scattered knowledge and puts it together into a highly detailed and comprehensible framework. I must admit that I was the most uncomfortable after reading this particular chapter, too, because I for the first time realized just how many clever ways there are to subvert kernels. I poked around one of my own Linux systems afterwards to try the things that Ed covered in an attempt to assure myself that the system had not been subverted at the kernel layer. I found that after reading this chapter, I was able to do this surprisingly well for someone who spends most of his time dealing with Windows, not Linux systems. Chapter 10 (on scenarios), applies what Ed has covered in the first nine chapters. Scenarios and case studies are the best way to "bring concepts home," and Ed has done that in a very nice way in the scenarios chapter. It is always interesting to learn about malicious code, but if you do not know what to do about it when you are through reading, you really haven't benefited. This whole book establishes that effective, proven, and workable solutions against this threat are available and describes in great detail how these solutions can be implemented.

I have never seen such a group of issues of the nature of the ones covered in Malware: Fighting Malicious Code so clearly and systematically presented. Ed is a top-rated SANS faculty member, and if you have any doubt that he can write as well as he can lecture, reading this book should completely remove it. His ability to present all the relevant technical details so understandably but without diluting the technical content is one that few authors have. His frequent injection of humorous statements is "topping on the cake," keeping the interest level high no matter how technical the subject matter. I keep thinking about how much more students who have taken various computer security courses from me over the years would have gotten out of these courses had this book been available earlier.

--E. Eugene Schultz, Ph.D., CISSP, CISM