You work as a Penetration Tester for the Infosec Inc. Your company takes the projects of security auditing. Recently, your company has assigned you a…

The Idle Scan technique's reliability is critically dependent on the "zombie" host being truly idle, meaning it is not generating other network traffic. The scan deduces a port's state by observing changes in the zombie's IP Identification (IPID) field. If the zombie is actively communicating with other systems, it will generate its own packets, causing its IPID to increment independently of the penetration tester's scan probes. This unrelated traffic ("noise") leads to unpredictable IPID increments, sometimes by more than one, rendering the scan results unreliable and matching the behavior described in the scenario.

A. The zombie does not need a direct connection to the target server; the scan operates by spoofing the zombie's IP, relying on standard IP routing.
C. This is factually incorrect. Hping is a powerful packet-crafting tool that can be used to perform manual idle scans, even though Nmap is more commonly used for automating the process.
D. A firewall blocking the scan would likely result in consistent behavior (e.g., all ports appearing filtered), not the observed unpredictable, multi-value increments of the IPID.

1. Nmap.org (Official Vendor Documentation): In the official documentation for Nmap's Idle Scan

it is explicitly stated: "If the zombie is carrying on much unrelated traffic

its IPID sequence number will increase on its own. This noise can make it difficult for Nmap to determine whether your probe packets have had an effect." This directly confirms that a non-idle zombie interacting with other systems is the cause of the problem.

Source: Nmap Reference Guide

Chapter 15

Port Scanning Techniques and Algorithms

Section: "Idle Scan (-sI)". Retrieved from https://nmap.org/book/man-idle-scan.html.

2. SANS Institute (GIAC-Related Academic Publication): A GIAC Gold Paper on advanced scanning techniques highlights the primary requirement for a successful idle scan. "The main requirement for this scan is an idle host on the network that has a predictable IP ID sequence... If the host is not idle

the results will be unreliable."

Source: Calderon

P. (2012). Advanced Nmap. SANS Institute InfoSec Reading Room. Page 11. Retrieved from https://www.sans.org/white-papers/34132/.

3. University Courseware: Lecture materials from reputable computer science programs explain this principle. The zombie host must be idle so that the only increments to its IPID are those caused by responses to the attacker's probes. Any other traffic generated by the zombie will corrupt the measurement.

Source: University of California

Berkeley. CS 161: Computer Security

Lecture 11: "Network Security". The slides discuss the Idle Scan mechanism and its reliance on a quiet/idle zombie for accurate results.