Modeling Botnet Propagation Using Time Zones

Monday, February 6. 2006
Another interesting paper from NDSS'06 is "Modeling Botnet Propagation Using Time Zones" by David Dagon, Cliff Zou, and Wenke Lee. They introduce a diurnal model of botnet propagation, i.e., a model which includes information about timezone and time of day to predict the propagation of a botnet. Real-world data verify this model and show that the time of day indeed influences botnet propagation. I also examined this phenomenon - more on that in the next blog entry...

Abstract
Time zones play an important and unexplored role in malware epidemics. To understand how time and location affect malware spread dynamics, we studied botnets, or large coordinated collections of victim machines (zombies) controlled by attackers. Over a six month period we observed dozens of botnets representing millions of victims. We noted diurnal properties in botnet activity, which we suspect occurs because victims turn their computers off at night. Through binary analysis, we also confirmed that some botnets demonstrated a bias in infecting regional populations.

Clearly, computers that are offline are not infectious, and any regional bias in infections will affect the overall growth of the botnet. We therefore created a diurnal propagation model. The model uses diurnal shaping functions to capture regional variations in online vulnerable populations.

The diurnal model also lets one compare propagation rates for different botnets, and prioritize response. Because of variations in release times and diurnal shaping functions particular to an infection, botnets released later in time may actually surpass other botnets that have an advanced start. Since response times for malware outbreaks is now measured in hours, being able to predict short-term propagation dynamics lets us allocate resources more intelligently. We
used empirical data from botnets to evaluate the analytical model.

Continue reading "Modeling Botnet Propagation Using Time Zones "

Malicious Malware: Attacking the Attackers, Part 2

Monday, February 6. 2006
The second part of the article on "Malicious Malware: Attacking the Attackers" is now available at securityfocus.

Scalability of nepenthes

Saturday, February 4. 2006
I did some further examination on the scalability of nepenthes. The testbed is a 2.4GHz Pentium III system with 2 GB of physical memory and a 100 MB Ethernet NIC. The system is running on Debian with Linux kernel 2.6.12 and nepenthes 0.1.5 in default configuration. I tested this setup with an increasing number of IP addresses assigned to nepenthes - ranging from just 256 up to more than 32,000. I measured the number of established TCP connections and system load for a period of one hour. This measurement was repeated three times to cancel out statistical effects or burst in the network traffic. The results are plotted in the following two figures:

Average number of established TCP connections


Average system load


As you can see, the scalability is rather good: At the beginning, it is (nearly) linear. However, when the system load reaches 1, the system is occupied with I/O operations and thus the number of established connections decreases. With better hardware (especially processor and NIC), the scalability would be better. Since nepenthes can also be deployed in a distributed way, more flexibility is possible...

Malicious Malware: Attacking the Attackers

Wednesday, February 1. 2006
There is a new article on securityfocus from Frederic Raynal and me entitled "Malicious Malware: Attacking the Attackers". In this article, we turn the table and take a look at possible ways to use malware or other offensive options (e.g. fake exploits) to stop an attacker. It's an overview of what we have seen in the past few years in this area and is written in a rather informal style.

Abstract:
This article explores measures to attack those malicious attackers who seek to harm our legitimate systems. The proactive use of exploits and bot networks that fight other bot networks, along with social engineering and attacker techniques are all discussed in an ethical manner. Part one of two.

The second part will be published in the next few days and Fyodor has just released Nmap 4.0.