The answer is that the access-group "OUTSIDE_IN" is applied to the wrong interface or direction, blocking legitimate outbound traffic. This occurs because the access-group is an inbound rule on the outside interface, meaning it inspects traffic entering that interface from the external network; when an internal host at 10.10.10.10 sends outbound traffic to 209.165.200.225 on port 80, the firewall sees the packet as leaving the inside interface and arriving at the outside interface from the inside, but the inbound access-list on the outside interface evaluates the packet as if it were coming from the outside, incorrectly denying it. On the CompTIA SecurityX CAS-004 exam, this scenario tests your understanding of firewall directionality and interface-based access control, often appearing as a syslog analysis question where a denied outbound flow is traced to a misapplied access-group. A common trap is assuming an access-list named "OUTSIDE_IN" must be correct for external traffic, but the key is matching the rule’s direction to the traffic flow. Remember the memory tip: "Inbound on outside blocks what comes from outside; outbound on inside lets your traffic ride."
CAS-004 Security Engineering Practice Question
This CAS-004 practice question tests your understanding of security engineering. 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
Refer to the exhibit.
=== syslog excerpt ===
Mar 15 14:23:45 firewall1 %ASA-4-106023: Deny tcp src inside:192.168.1.10/54321 dst outside:10.0.0.1/80 by access-group "OUTSIDE_IN" [0x0, 0x0]
Mar 15 14:23:46 firewall1 %ASA-4-106023: Deny tcp src inside:192.168.1.10/54322 dst outside:10.0.0.1/80 by access-group "OUTSIDE_IN" [0x0, 0x0]
Mar 15 14:23:47 firewall1 %ASA-4-106023: Deny tcp src inside:192.168.1.10/54323 dst outside:10.0.0.1/80 by access-group "OUTSIDE_IN" [0x0, 0x0]
A security analyst reviews the syslog messages from the company's ASA firewall. Based on the exhibit, which of the following 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.
Refer to the exhibit.
=== syslog excerpt ===
Mar 15 14:23:45 firewall1 %ASA-4-106023: Deny tcp src inside:192.168.1.10/54321 dst outside:10.0.0.1/80 by access-group "OUTSIDE_IN" [0x0, 0x0]
Mar 15 14:23:46 firewall1 %ASA-4-106023: Deny tcp src inside:192.168.1.10/54322 dst outside:10.0.0.1/80 by access-group "OUTSIDE_IN" [0x0, 0x0]
Mar 15 14:23:47 firewall1 %ASA-4-106023: Deny tcp src inside:192.168.1.10/54323 dst outside:10.0.0.1/80 by access-group "OUTSIDE_IN" [0x0, 0x0]
A
The external server is trying to initiate connections to the internal host on port 80.
Why wrong: The log shows source IP from inside, so the connections originate from inside.
B
Network address translation (NAT) is not configured correctly for the internal host.
Why wrong: NAT issues would typically not cause a deny by an access-group; they would cause unreachability or translation failures.
C
The access-group "OUTSIDE_IN" is applied to the wrong interface or direction, blocking legitimate outbound traffic.
The access list name suggests it is meant for inbound traffic on the outside interface, but it is blocking outbound traffic, indicating a misapplication.
D
The internal host is attempting a port scan against the external server.
Why wrong: Multiple connections to the same destination IP and port could be a scan, but the log shows only a few connections, and the problem is likely a rule misconfiguration.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The access-group "OUTSIDE_IN" is applied to the wrong interface or direction, blocking legitimate outbound traffic.
The syslog message shows traffic from the internal host (10.10.10.10) to the external server (209.165.200.225) on port 80 being denied by the access-group "OUTSIDE_IN" applied to the outside interface. Since the traffic is outbound (source inside, destination outside), an inbound access-list on the outside interface would block this legitimate outbound traffic because it evaluates packets entering the interface from the outside, not leaving it. The correct configuration would be to apply the access-group to the inside interface in the inbound direction or to the outside interface in the outbound direction.
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 external server is trying to initiate connections to the internal host on port 80.
Why it's wrong here
The log shows source IP from inside, so the connections originate from inside.
✗
Network address translation (NAT) is not configured correctly for the internal host.
Why it's wrong here
NAT issues would typically not cause a deny by an access-group; they would cause unreachability or translation failures.
✓
The access-group "OUTSIDE_IN" is applied to the wrong interface or direction, blocking legitimate outbound traffic.
Why this is correct
The access list name suggests it is meant for inbound traffic on the outside interface, but it is blocking outbound traffic, indicating a misapplication.
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.
✗
The internal host is attempting a port scan against the external server.
Why it's wrong here
Multiple connections to the same destination IP and port could be a scan, but the log shows only a few connections, and the problem is likely a rule misconfiguration.
Common exam traps
Common exam trap: answer the scenario, not the keyword
CompTIA often tests the concept that an access-list applied inbound on the outside interface filters traffic entering from the outside, not traffic leaving the inside, causing candidates to mistakenly think the ACL blocks inbound traffic when it actually blocks outbound traffic.
Trap categories for this question
Command / output trap
The log shows source IP from inside, so the connections originate from inside.
Detailed technical explanation
How to think about this question
Cisco ASA access-lists are applied to interfaces with a direction (in or out) relative to the interface. When an access-group is applied inbound on the outside interface, it filters traffic entering the ASA from the external network; outbound traffic from inside hosts exits via the outside interface and is not evaluated by an inbound ACL on that interface unless it is reflected or statefully inspected. In this scenario, the ACL "OUTSIDE_IN" is likely intended to filter inbound traffic but is misapplied, causing it to block outbound traffic that should be allowed. Real-world misconfigurations often occur when administrators apply ACLs to the wrong interface or direction, leading to silent failures that are only detected via syslog analysis.
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 small business has 20 workstations on the 192.168.1.0/24 network and one public IP from its ISP. The router uses PAT (NAT overload) so all 20 devices share one public address using different source ports. NAT questions test whether you understand the four address terms and which direction each translation applies.
What to study next
Got this wrong? Here's your next step.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Security Engineering — This question tests Security Engineering — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The access-group "OUTSIDE_IN" is applied to the wrong interface or direction, blocking legitimate outbound traffic. — The syslog message shows traffic from the internal host (10.10.10.10) to the external server (209.165.200.225) on port 80 being denied by the access-group "OUTSIDE_IN" applied to the outside interface. Since the traffic is outbound (source inside, destination outside), an inbound access-list on the outside interface would block this legitimate outbound traffic because it evaluates packets entering the interface from the outside, not leaving it. The correct configuration would be to apply the access-group to the inside interface in the inbound direction or to the outside interface in the outbound direction.
What should I do if I get this CAS-004 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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