An Investigation into Collaborative Scanners

Manually detecting and tracking collaborative scanners’ behaviour over a prolonged period

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Abstract

Port scanning is a technique often used by adversaries to detect vulnerable services running on a machine. There are defense mechanisms in place that can detect fast, single-source port scanning, but one of the ways to remain hidden is to distribute the scan between multiple hosts. These distributed groups of machines can divide the address space and collaboratively scan the whole Internet within minutes and remain relatively hidden.
This paper proposes a simple method to detect these collaborative scanners based on the TCP/IP header and demonstrates its efficiency. It also tracks these scanners for a longer period and describes their behavior and how they develop over time. This includes the infrastructure they utilize, the specific ports they target, and additional relevant details. This perspective has not been previously explored in the academic literature and we find it to be important such that defenders get a better understanding of the threats they are facing.