The answer is a port scan, as the firewall logs show a single source IP (10.0.0.2) sending denied traffic to a single destination IP (192.168.1.10) across multiple distinct destination ports like 22, 80, and 443 within a compressed time window. This sequential probing of different ports is the hallmark of a reconnaissance technique used by attackers to map open services, and firewalls detect this pattern to block such scanning behavior. On the CISSP exam, this scenario tests your understanding of network security monitoring and intrusion detection, often appearing in questions about log analysis or attack identification. A common trap is to mistake this for a misconfigured service or a typo, but the key clue is the variety of ports targeted from one source in rapid succession. Memory tip: think “One IP, many ports, short time” equals a port scan.
CISSP Security Operations Practice Question
This CISSP practice question tests your understanding of security operations. This is a configuration task: choose the command set that satisfies every stated requirement. Small differences — like 'secret' vs 'password' or 'transport input ssh' vs 'all' — change whether the answer is correct. 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.
Exhibit
Mar 15 08:20:00 firewall1: %ASA-4-106023: Deny tcp src outside:203.0.113.5/1234 dst inside:10.0.0.10/80 by access-group "OUTSIDE_IN"
Mar 15 08:20:01 firewall1: %ASA-4-106023: Deny tcp src outside:203.0.113.5/1235 dst inside:10.0.0.10/80 by access-group "OUTSIDE_IN"
Mar 15 08:20:02 firewall1: %ASA-4-106023: Deny tcp src outside:203.0.113.5/1236 dst inside:10.0.0.10/80 by access-group "OUTSIDE_IN"
Refer to the exhibit. What is the most likely cause of the denied traffic?
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
✓
The source IP is attempting a port scan
The exhibit shows a firewall log where traffic from a single source IP (10.0.0.2) to a single destination IP (192.168.1.10) is denied on multiple different destination ports (e.g., 22, 80, 443) within a short time window. This pattern of sequential probes to distinct ports is characteristic of a port scan, which firewalls often detect and block as a reconnaissance attempt. The firewall rule is likely configured to deny such scanning behavior, not just a single port or typo.
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 firewall rule has a typo
Why it's wrong here
Unlikely as only this source IP is being denied.
✓
The source IP is attempting a port scan
Why this is correct
Multiple source ports to same destination indicates scanning behavior.
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.
Port 80 is typically allowed; the logs show multiple source ports.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates see multiple denied ports and assume the destination port is not allowed, missing the contextual clue of sequential probes from one source that indicates a port scan rather than a simple access control list issue.
Trap categories for this question
Command / output trap
Port 80 is typically allowed; the logs show multiple source ports.
Detailed technical explanation
How to think about this question
Port scans are detected by firewalls using stateful inspection or intrusion prevention features that track the number of unique destination ports from a single source within a defined time threshold (e.g., 10 ports in 5 seconds). The firewall may apply a 'deny' action based on a security policy that blocks scanning behavior, often referencing RFC 2827 or best practices for ingress filtering. In real-world scenarios, such logs help identify compromised internal hosts or external reconnaissance before an actual attack.
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.
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: The source IP is attempting a port scan — The exhibit shows a firewall log where traffic from a single source IP (10.0.0.2) to a single destination IP (192.168.1.10) is denied on multiple different destination ports (e.g., 22, 80, 443) within a short time window. This pattern of sequential probes to distinct ports is characteristic of a port scan, which firewalls often detect and block as a reconnaissance attempt. The firewall rule is likely configured to deny such scanning behavior, not just a single port or typo.
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.
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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