Outsiders versus Insiders: What Is NSM's Focus?
This book is about network security monitoring. I use the term network to emphasize the book's focus on traffic and incidents that occur over wires, radio waves, and other media. This book does not address intruders who steal data by copying it onto a USB memory stick or burning it to a CD-ROM. Although the focus for much of the book is on outsiders gaining unauthorized access, it pertains equally well to insiders who transfer information to remote locations. In fact, once an outsider has local access to an organization, he or she looks very much like an insider. 
Should this book (and NSM) pay more attention to insiders? One of the urban myths of the computer security field holds that 80% of all attacks originate from the inside. This "statistic" is quoted by anyone trying to sell a product that focuses on detecting attacks by insiders. An analysis of the most respected source of computer security statistics, the Computer Crime and Security Survey conducted annually by the Computer Security Institute (CSI) and the FBI, sheds some light on the source and interpretation of this figure. 
The 2001 CSI/FBI study quoted a commentary by Dr. Eugene Schultz that first appeared in the Information Security Bulletin. Dr. Schultz was asked:
I keep hearing statistics that say that 80 percent of all attacks are from the inside. But then I read about all these Web defacements and distributed denial of service attacks, and it all doesn't add up. Do most attacks really originate from the inside?
Dr. Schultz responded:
There is currently considerable confusion concerning where most attacks originate. Unfortunately, a lot of this confusion comes from the fact that some people keep quoting a 17-year-old FBI statistic that indicated that 80 percent of all attacks originated from the [inside]. . . . Should [we] ignore the insider threat in favor of the outsider threat? On the contrary. The insider threat remains the greatest single source of risk to organizations. Insider attacks generally have far greater negative impact to business interests and operations. Many externally initiated attacks can best be described as ankle-biter attacks launched by script kiddies.
But what I am also saying is that it is important to avoid underestimating the external threat. It is not only growing disproportionately, but is being fueled increasingly by organized crime and motives related to espionage. I urge all security professionals to conduct a first-hand inspection of their organization's firewall logs before making a claim that most attacks come from the inside. Perhaps most successful attacks may come from the inside (especially if an organization's firewalls are well configured and maintained), true, but that is different from saying that most attacks originate from the inside. 
Dr. Dorothy Denning, some of whose papers are discussed in Appendix B, confirmed Dr. Shultz's conclusions. Looking at the threat, noted by the 2001 CSI/FBI study as "likely sources of attack," Dr. Denning wrote in 2001:
For the first time, more respondents said that independent hackers were more likely to be the source of an attack than disgruntled or dishonest insiders (81% vs. 76%). Perhaps the notion that insiders account for 80% of incidents no longer bears any truth whatsoever. 
The 2002 and 2003 CSI/FBI statistics for "likely sources of attack" continued this trend. At this point, remember that the statistic in play is "likely sources of attack," namely the party that embodies a threat. In addition to disgruntled employees and independent hackers, other "likely sources of attack" counted by the CSI/FBI survey include foreign governments (28% in 2003), foreign corporations (25%), and U.S. competitors (40%).
Disgruntled employees are assumed to be insiders (i.e., people who can launch attacks from inside an organization) by definition. Independent hackers are assumed to not be insiders. But from where do attacks actually originate? What is the vector to the target? The CSI/FBI study asks respondents to rate "internal systems," "remote dial-in," and "Internet" as "frequent points of attack." In 2003, 78% cited the Internet, while only 30% cited internal systems and 18% cited dial-in attacks. In 1999 the Internet was cited at 57% while internal systems rated 51%. These figures fly in the face of the 80% statistic.
A third figure hammers the idea that 80% of all attacks originate from the inside. The CSI/FBI study asks for the origin of incidents involving Web servers. For the past five years, incidents caused by insiders accounted for 7% or less of all Web intrusions. In 2003, outsiders accounted for 53%. About one-quarter of respondents said they "don't know" the origin of their Web incidents, and 18% said "both" the inside and outside participated.
At this point the idea that insiders are to blame should be losing steam. Still, the 80% crowd can find solace in other parts of the 2003 CSI/FBI study. The study asks respondents to rate "types of attack or misuse detected in the last 12 months." In 2003, 80% of participants cited "insider abuse of net access" as an "attack or misuse," while only 36% confirmed "system penetration." "Insider abuse of net access" apparently refers to inappropriate use of the Internet; as a separate statistic, "unauthorized access by insiders" merited a 45% rating.
If the insider advocates want to make their case, they should abandon the 80% statistic and focus on financial losses. The 2003 CSI/FBI study noted "theft of proprietary information" cost respondents over $70 million; "system penetration" cost a measly $2.8 million. One could assume that insiders accounted for this theft, but that might not be the case. The study noted "unauthorized access by insiders" cost respondents only $406,000 in losses. 
Regardless of your stance on the outsider versus insider issue, any activity that makes use of the network is a suitable focus for analysis using NSM. Any illicit action that generates a packet becomes an indicator for an NSM operation. One of the keys to devising a suitable NSM strategy for your organization is understanding certain tenets of detection, outlined next.