The answer is a SYN flood DDoS attack and a stateful firewall blocking the connection. When you see repeated TCP SYN packets without any SYN-ACK responses, it indicates the target is either overwhelmed by a flood of half-open connections, exhausting its resources, or a security device is silently dropping the SYN packets before a handshake can complete. On the CompTIA SecurityX CAS-402 exam, this scenario tests your ability to differentiate between network-based attacks and legitimate security controls—a common trap is assuming the host is simply down, but the absence of any response (even a RST) points to a filter or attack. Remember that a stateful firewall will drop unsolicited SYN packets if no matching session exists, while a SYN flood deliberately never completes the three-way handshake. Memory tip: “No SYN-ACK? Check for attack or firewall stack.”
CAS-004 Security Operations Practice Question
This CAS-004 practice question tests your understanding of security operations. 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 security analyst is analyzing a network capture and sees repeated TCP SYN packets to a host but no SYN-ACK responses. Which TWO conclusions are MOST likely? (Choose two.)
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "most likely"
Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
A firewall is dropping the SYN packets before they reach the host.
Options A and D are correct. A SYN flood without response suggests a DDoS attack (A) or a stateful firewall blocking (D). Option B is incorrect because no SYN-ACK means no connection established. Option C is unrelated. Option E is possible but less likely than the top two.
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.
✗
The host is out of TCP receive window space.
Why it's wrong here
This would cause connection issues but not complete lack of SYN-ACK.
✗
The network has a loop causing packet duplication.
Why it's wrong here
Loop would cause duplicate packets but not missing SYN-ACKs.
✗
The host has accepted the connections.
Why it's wrong here
No SYN-ACK indicates connections not accepted.
✓
A firewall is dropping the SYN packets before they reach the host.
Why this is correct
Firewalls can block incoming SYN packets, resulting in no response.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
✓
An attacker is performing a SYN flood DDoS attack.
Why this is correct
SYN flood generates many SYN packets without completing handshake.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Many certification questions include familiar terms but test a specific constraint. Read the exact wording before choosing an answer that is generally true but wrong for this case.
Detailed technical explanation
How to think about this question
This question should be treated as a scenario, not a definition check. Identify the problem, the constraint and the best action. Then compare each option against those facts.
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.
Use explanations to understand the rule behind the answer.
TExam Day Tips
→Underline the problem statement mentally.
→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 practitioner preparing for the CAS-004 exam encounters this exact type of scenario on the job. The correct answer here is not the most general option — it is the best answer for the specific constraint described. Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option. Real exam questions reward reading the full scenario before eliminating options, because the constraint defines which answer fits.
What to study next
Got this wrong? Here's your next step.
Identify which CAS-004 exam domain this question belongs to, then review the specific concept being tested. Practise related questions in that domain and focus on understanding why each wrong answer is tempting — not just why the correct answer is right.
Security Operations — This question tests Security Operations — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: A firewall is dropping the SYN packets before they reach the host. — Options A and D are correct. A SYN flood without response suggests a DDoS attack (A) or a stateful firewall blocking (D). Option B is incorrect because no SYN-ACK means no connection established. Option C is unrelated. Option E is possible but less likely than the top two.
What should I do if I get this CAS-004 question wrong?
Identify which CAS-004 exam domain this question belongs to, then review the specific concept being tested. Practise related questions in that domain and focus on understanding why each wrong answer is tempting — not just why the correct answer is right.
Are there clue words in this question I should notice?
Yes — watch for: "most likely". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
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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