The answer is a missing firewall rule allowing RDP traffic. This is correct because the log entry shows a packet destined for TCP port 3389, the standard port for Remote Desktop Protocol, being denied by the access-group named 'outside_in'. When a firewall denies traffic without an explicit permit statement in its access control list, it indicates that no rule exists to authorize that specific service, causing the default implicit deny action to block the connection. On the CISA exam, this scenario tests your ability to interpret firewall logs and correlate denied traffic with missing or misconfigured rules—a common audit finding when reviewing network perimeter controls. A frequent trap is assuming the denial is due to an incorrect source IP or a security threat, but the log itself points to a policy gap. Remember the memory tip: "3389 denied? Check the rule, not the line."
CISA Information System Auditing Process Practice Question
This CISA practice question tests your understanding of information system auditing process. 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.
```
Feb 20 10:15:32 firewall %ASA-4-106023: Deny tcp src outside:10.0.0.1/3389 dst inside:192.168.1.100/3389 by access-group "outside_in" [0x0, 0x0]
```
An IS auditor reviews 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.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Missing firewall rule allowing RDP traffic
The log shows an RDP connection (port 3389) being denied by the access-group 'outside_in', indicating that no rule permits this traffic.
Key principle: NAT direction and interface roles matter as much as the IP address mapping. Inside/outside designation controls which traffic is translated.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✗
Misconfigured VPN tunnel
Why it's wrong here
VPN issues would not be logged as an access-group deny.
✗
Intrusion prevention system blocking
Why it's wrong here
IPS blocks would appear with different log signatures.
✓
Missing firewall rule allowing RDP traffic
Why this is correct
The deny log specifically references the access-group, implying a rule is missing.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Static NAT maps one inside address to one outside address.
✗
Incorrect NAT configuration
Why it's wrong here
NAT configuration is not directly indicated by this log message.
Common exam traps
Common exam trap: NAT rules depend on direction and matching traffic
NAT is not only about the public address. The inside/outside interface roles and the ACL or rule that matches traffic are just as important.
Detailed technical explanation
How to think about this question
NAT questions usually test address translation, overload/PAT behaviour, static mappings and whether the right traffic is being translated. Read the interface direction and address terms carefully.
KKey Concepts to Remember
Static NAT maps one inside address to one outside address.
PAT allows many inside hosts to share one public address using ports.
Inside local and inside global describe the private and translated addresses.
NAT ACLs identify traffic for translation, not always security filtering.
TExam Day Tips
→Identify inside and outside interfaces first.
→Check whether the scenario needs static NAT, dynamic NAT or PAT.
→Do not confuse NAT matching ACLs with normal packet-filtering intent.
Key takeaway
NAT direction and interface roles matter as much as the IP address mapping. Inside/outside designation controls which traffic is translated.
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.
Review the four NAT address types (inside local, inside global, outside local, outside global), PAT port overload, and static vs dynamic NAT use cases. Then practise related CISA NAT questions on configuration and troubleshooting.
Information System Auditing Process — This question tests Information System Auditing Process — Static NAT maps one inside address to one outside address..
What is the correct answer to this question?
The correct answer is: Missing firewall rule allowing RDP traffic — The log shows an RDP connection (port 3389) being denied by the access-group 'outside_in', indicating that no rule permits this traffic.
What should I do if I get this CISA question wrong?
Review the four NAT address types (inside local, inside global, outside local, outside global), PAT port overload, and static vs dynamic NAT use cases. Then practise related CISA NAT questions on configuration and troubleshooting.
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?
Static NAT maps one inside address to one outside address.
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