The answer is a SYN flood attack. This is correct because a SYN flood exploits the TCP three-way handshake by sending a massive volume of SYN packets to a target, often from a compromised host or with spoofed source IPs, which exhausts the server’s connection table and prevents legitimate handshake completions. On the CISSP exam, this scenario tests your understanding of network-based denial-of-service attacks, specifically how an IDS alert for high SYN traffic to a single external IP points to resource exhaustion rather than a protocol flaw. A common trap is confusing this with a Smurf attack, which uses ICMP echo requests, or a TCP reset attack; remember that SYN floods target the half-open connection queue. For a memory tip, think “SYN = Saturate Your Network” to recall that the attack floods the initial handshake step to block legitimate access.
CISSP Communication and Network Security Practice Question
This CISSP practice question tests your understanding of communication and network security. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
A network security analyst receives an alert from the intrusion detection system (IDS) indicating a high volume of TCP SYN packets to a single external IP address from a compromised internal host. This is characteristic of which type of attack?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
SYN flood
A SYN flood attack exploits the TCP three-way handshake by sending a high volume of SYN packets to a target, exhausting its connection table and preventing legitimate connections. The IDS alert specifically describes a compromised internal host generating many SYN packets to a single external IP, which matches the classic behavior of a SYN flood where the attacker spoofs the source IP or uses a bot to saturate the target's resources.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✓
SYN flood
Why this is correct
A SYN flood uses a high volume of TCP SYN packets to overwhelm the target's connection queue.
Related concept
Read the scenario before looking for a memorised answer.
✗
Man-in-the-middle
Why it's wrong here
Man-in-the-middle attacks involve intercepting communication between two parties, not sending a flood of packets.
✗
ARP spoofing
Why it's wrong here
ARP spoofing manipulates ARP tables to intercept local traffic, not associated with SYN floods.
✗
DNS amplification
Why it's wrong here
DNS amplification uses small queries to generate large responses, typically over UDP, not SYN packets.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates confuse a SYN flood (which uses TCP SYN packets to exhaust resources) with a DNS amplification attack (which uses UDP and reflection), but the question's mention of 'TCP SYN packets' directly points to the SYN flood, not a volumetric reflection attack.
Detailed technical explanation
How to think about this question
In a SYN flood, the attacker sends SYN packets with spoofed source IPs (or from a compromised host) to the target, which responds with SYN-ACKs and waits for the final ACK in the half-open connection queue. The target's backlog queue fills up, and if the attack rate exceeds the system's ability to time out entries (typically 30–60 seconds per RFC 793), new legitimate connections are denied. Real-world SYN floods often use botnets to generate millions of packets per second, overwhelming even stateful firewalls that track connection states.
KKey Concepts to Remember
Read the scenario before looking for a memorised answer.
Find the constraint that changes the correct option.
Eliminate answers that are true in general but not in this case.
TExam Day Tips
→Watch for words such as best, first, most likely and least administrative effort.
→Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
How this comes up in practice
A security team runs a vulnerability scan on a web application and discovers an unpatched SQL injection flaw. The team prioritises remediation by CVSS score — critical flaws are patched within 24 hours, high within 7 days. Questions like this test whether you understand vulnerability management processes, scanning tools, and remediation prioritisation.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this CISSP question in full detail.
Communication and Network Security — This question tests Communication and Network Security — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: SYN flood — A SYN flood attack exploits the TCP three-way handshake by sending a high volume of SYN packets to a target, exhausting its connection table and preventing legitimate connections. The IDS alert specifically describes a compromised internal host generating many SYN packets to a single external IP, which matches the classic behavior of a SYN flood where the attacker spoofs the source IP or uses a bot to saturate the target's resources.
What should I do if I get this CISSP question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Question Discussion
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