Monitoring tools like Intrusion Detection Systems (IDS), Firewalls, or Honeypots are a second line of defense in the face of an increasing number of distributed, increasingly sophisticated, and targeted attacks. A huge amount of security alerts needs to be analyzed and correlated to gather the complete picture of an attack. However, most conventional IDS fall short in correlating alerts that have different sources, so that many distributed attacks remain completely unnoticed. In this paper, we define alert correlation as a process and describe the consecutive steps along with their properties and goals. Following this process, we propose
Graph-based Alert Correlation (GAC),
a novel correlation algorithm that isolates attacks, identifies attack scenarios, and assembles multi-stage attacks from huge alert sets. Our evaluation results on artificial and real-world data indicates that
GAC
is robust against false positives, can detect distributed attacks, and scales with an increasing number of alerts.
An Intrusion Detection System (IDS) to secure computer networks reports indicators for an attack as alerts. However, every attack can result in a multitude of IDS alerts that need to be correlated to see the full picture of the attack. In this paper, we present a correlation approach that transforms clusters of alerts into a graph structure on which we compute signatures of network motifs to characterize these clusters. A motif representation of attack characteristics is magnitudes smaller than the original alert data, but still allows to efficiently compare and correlate attacks with each other and with reference signatures. This allows not only to identify known attack scenarios, e.g., DDoS, scan, and worm attacks, but also to derive new reference signatures for unknown scenarios. Our results indicate a reliable identification of scenarios, even when attacks differ in size and at least slightly in their characteristics. Applied on real-world alert data, our approach can classify and assign attack scenarios of up to 96% of all attacks and can represent their characteristics using 1% of the size of the full alert data.
The ever-growing number of cyber attacks from botnets has made them one of the biggest threats on the Internet. Thus, it is crucial to study and analyze botnets, to take them down. For this, an extensive monitoring is a pre-requisite for preparing a botnet takedown, e.g., via a sinkholing attack. However, every new monitoring mechanism developed for botnets is usually tackled by the botmasters by introducing novel antimonitoring countermeasures. In this paper, we anticipate these countermeasures by proposing a set of lightweight techniques for detecting the presence of crawlers in P2P botnets, called BoobyTrap. For that, we exploit botnet-specific protocol and design constraints. We evaluate the performance of our BoobyTrap mechanism on two real-world botnets: Sality and ZeroAccess.Our results indicate that we can distinguish many crawlers from benign bots. In fact, we discovered close to 10 crawler nodes within our observation period in the Sality botnet and around 120 in the ZeroAccess botnet. In addition, we also describe the observable characteristics of the detected crawlers and suggest crawler improvements for enabling monitoring in the presence of the BoobyTrap mechanism.
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