CREST Practitioner Security Analyst (CPSA) Practice 2025 - Free CPSA Practice Questions and Study Guide

The primary technique employed in active OS fingerprinting is sending specially crafted packets. This method involves a security analyst actively probing the target system by dispatching packets that contain specific characteristics. The responses received from the target are then analyzed to interpret the operating system in use based on the unique behaviors and responses elicited by those packets.

This technique stands out because it allows for a high degree of accuracy in identifying operating systems compared to passive methods. By carefully crafting packets, analysts can take advantage of the different ways operating systems respond to various types of network traffic, which is integral to OS detection.

In contrast, analyzing open ports tends to provide information about services running on a machine but does not directly indicate the operating system. Observing passive traffic generally captures information on already occurring communications without engaging with the systems, which may not yield conclusive data on the OS. Monitoring login attempts focuses specifically on authentication processes and does not provide broader insights into the operating system itself. Consequently, sending specially crafted packets is the most effective way to actively fingerprint an OS, highlighting its essential role in network security assessments.