The correct interpretation is that the workstation attempted to access a web server on the internet and the traffic was blocked by an inbound ACL. This is because the log entry shows a denied packet from source IP 192.168.1.10 to a public destination on port 80, but in firewall terminology, an inbound ACL filters traffic entering an interface—here, the return traffic from the web server back to the workstation is being blocked on the external interface. On the CISSP exam, this tests your ability to distinguish between inbound and outbound ACLs in firewall log interpretation, a common trap being that candidates assume the source IP indicates the direction of the original request rather than the logged packet’s direction. Remember that an inbound ACL on an external interface controls what comes in from the internet, so if a private IP appears as the source in a denied entry, it often means the response to an outbound request was blocked. A useful memory tip: “Inbound blocks the reply, outbound blocks the try.”
CISSP Security Operations Practice Question
This CISSP 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.
Exhibit
Refer to the exhibit.
Exhibit: syslog entry from a firewall
<134>2024-03-15T14:23:45Z FW-01 %ASA-4-106023: Deny tcp src inside:192.168.1.10/3345 dst outside:203.0.113.5/80 by access-group "OUTSIDE_IN" [0x0, 0x0]
A network administrator finds the above log entry. The source IP 192.168.1.10 is a user workstation. What does this log entry indicate?
Refer to the exhibit.
Exhibit: syslog entry from a firewall
<134>2024-03-15T14:23:45Z FW-01 %ASA-4-106023: Deny tcp src inside:192.168.1.10/3345 dst outside:203.0.113.5/80 by access-group "OUTSIDE_IN" [0x0, 0x0]
A
An external host attempted to connect to the workstation on port 80
Why wrong: The source is inside and destination is outside; it's outbound traffic.
B
The firewall detected an intrusion attempt from the workstation
Why wrong: The log is a standard ACL deny, not an intrusion detection signature.
C
The workstation attempted to access a web server on the internet and the traffic was blocked by an inbound ACL
The ACL 'OUTSIDE_IN' is applied to the outside interface and denied the traffic.
D
The workstation successfully connected to a web server on the internet
Why wrong: The action is 'Deny', so the connection was blocked.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The workstation attempted to access a web server on the internet and the traffic was blocked by an inbound ACL
Option C is correct because the log entry shows a packet from source IP 192.168.1.10 (the workstation) to a destination IP on the internet with destination port 80 (HTTP), and the action taken by the firewall is 'denied' by an inbound ACL. In firewall terminology, an inbound ACL filters traffic entering an interface; here, the return traffic from the web server to the workstation is being blocked by the inbound ACL on the external interface, meaning the workstation's outbound request was allowed but the response was denied, indicating the workstation attempted to access a web server but the traffic was blocked.
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.
✗
An external host attempted to connect to the workstation on port 80
Why it's wrong here
The source is inside and destination is outside; it's outbound traffic.
✗
The firewall detected an intrusion attempt from the workstation
Why it's wrong here
The log is a standard ACL deny, not an intrusion detection signature.
✓
The workstation attempted to access a web server on the internet and the traffic was blocked by an inbound ACL
Why this is correct
The ACL 'OUTSIDE_IN' is applied to the outside interface and denied the traffic.
Related concept
Read the scenario before looking for a memorised answer.
✗
The workstation successfully connected to a web server on the internet
Why it's wrong here
The action is 'Deny', so the connection was blocked.
Common exam traps
Common exam trap: answer the scenario, not the keyword
ISC2 often tests the distinction between inbound and outbound ACLs, and the trap here is that candidates mistakenly think the source IP indicates the direction of the attack, leading them to choose Option A, when in fact the source IP is the internal workstation and the ACL is blocking the return traffic from the external web server.
Detailed technical explanation
How to think about this question
In Cisco ASA or similar firewalls, an inbound ACL on the outside interface filters traffic entering that interface from the internet; when a workstation initiates an outbound HTTP request, the firewall creates a stateful connection entry, but if the return traffic does not match the state (e.g., due to asymmetric routing or a misconfigured ACL), it is evaluated against the inbound ACL and may be denied. This scenario often occurs when the firewall is configured with a strict inbound ACL that blocks all inbound traffic by default, and the return packets from the web server are dropped because they are not part of an established session or the ACL lacks a permit statement for the return traffic.
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 SOC analyst notices unusual lateral movement in the network at 2 AM. The IR playbook dictates: identify and contain (isolate the affected machine), then eradicate (remove the malware), then recover (restore from backup), then document. Skipping containment before eradication risks the attacker regaining access. Questions like this test the sequence and rationale of incident response phases.
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 workstation attempted to access a web server on the internet and the traffic was blocked by an inbound ACL — Option C is correct because the log entry shows a packet from source IP 192.168.1.10 (the workstation) to a destination IP on the internet with destination port 80 (HTTP), and the action taken by the firewall is 'denied' by an inbound ACL. In firewall terminology, an inbound ACL filters traffic entering an interface; here, the return traffic from the web server to the workstation is being blocked by the inbound ACL on the external interface, meaning the workstation's outbound request was allowed but the response was denied, indicating the workstation attempted to access a web server but the traffic was blocked.
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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