CEH Practice Question: Malware, Social Engineering and Network Attacks
A security analyst runs the command 'tcpdump -i eth0 -n host 10.0.0.5 and port 80' and sees many packets with the SYN flag set but no corresponding ACK. Which attack is likely occurring?
⚠ Common exam trap
It's easy for candidates to confuse a SYN flood with a generic 'flood' attack (like ICMP or UDP flood) because they focus on the word 'flood' rather than the specific TCP handshake behavior indicated by the SYN flag without ACK.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
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SYN flood
The command captures TCP packets on port 80 with the SYN flag set but no corresponding ACK, which indicates that the target is receiving SYN requests but never completing the three-way handshake. This is the hallmark of a SYN flood attack, where the attacker sends a high volume of SYN packets to exhaust the server's connection queue, preventing legitimate connections.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
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SYN flood
Why this is correct
A SYN flood is characterized by an attacker sending a large volume of TCP SYN packets to a target server without completing the three-way handshake. The tcpdump -i eth0 -n host command would reveal a high rate of incoming TCP packets with the SYN flag set, directed at the specified host, but without corresponding SYN-ACK or ACK packets originating from the target. This pattern indicates numerous half-open connections accumulating on the target, exhausting its connection table resources.
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ICMP flood
Why it's wrong here
An ICMP flood, also known as a Smurf attack or ping flood, overwhelms a target with a massive number of ICMP echo request packets. The tcpdump command would display a high volume of traffic using the ICMP protocol, specifically type 8 (echo request) and type 0 (echo reply), directed to or from the specified host. This attack does not involve TCP SYN packets, making it distinctly different from a SYN flood.
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UDP flood
Why it's wrong here
A UDP flood attack involves saturating a target's network with a large volume of UDP packets, often directed at random ports or specific services. When observed with tcpdump -i eth0 -n host, the output would show a significant number of packets utilizing the UDP protocol, rather than TCP. There would be no indication of TCP SYN flags, as UDP is a connectionless protocol and does not employ the handshake mechanism.
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Ping of Death
Why it's wrong here
The Ping of Death attack exploits vulnerabilities in older systems by sending an oversized ICMP echo request packet that, when reassembled, exceeds the maximum allowed IP packet size (65,535 bytes). While tcpdump would show ICMP traffic, the defining characteristic would be the unusually large packet size and potential fragmentation, not a flood of standard TCP SYN packets. This attack targets system stability rather than connection table exhaustion.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This CEH practice question is part of Courseiva's free EC-Council certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the CEH exam.