The correct answer is the risk of data exfiltration via DNS tunneling. This is because the firewall rule permitting outbound DNS traffic on UDP/TCP port 53 to any external destination creates a covert channel; attackers can encode stolen data within DNS queries and responses, which are rarely inspected deeply, allowing sensitive information to bypass security controls undetected. On the Certified Information Security Manager CISM exam, this scenario tests your grasp of network security fundamentals and the principle that even allowed protocols can be weaponized—a common trap is assuming “permitted” equals “safe.” Remember the mnemonic “DNS = Data Never Safe” to recall that any unrestricted outbound protocol, especially DNS, is a prime vector for tunneling and exfiltration in risk assessments.
CISM Information Security Risk Management Practice Question
This CISM practice question tests your understanding of information security risk management. 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.
Exhibit:
```
CISCO ASA Firewall Config Snippet
access-list INSIDE extended permit tcp 10.0.0.0 255.255.255.0 any eq 443
access-list INSIDE extended permit udp 10.0.0.0 255.255.255.0 any eq 53
access-list OUTSIDE extended deny ip any any
```
Refer to the exhibit. A security analyst reviews the firewall configuration and identifies a potential risk. What is the most likely risk?
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
✓
Risk of data exfiltration via DNS tunneling.
The exhibit shows a firewall rule that permits DNS traffic (UDP/TCP port 53) from the internal network to any external destination. This configuration allows internal hosts to perform DNS queries to external servers, which can be exploited for DNS tunneling—a technique where data is encapsulated within DNS queries and responses to bypass security controls and exfiltrate sensitive information. Since DNS traffic is typically allowed through firewalls, this creates a covert channel for data exfiltration, making option D the most likely risk.
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.
✗
Risk of unauthorized external access to internal services.
Risk of denial-of-service attacks from internal hosts.
Why it's wrong here
DoS would require specific attack vectors, not just outbound rules.
✗
Risk of IP spoofing attacks from the inside network.
Why it's wrong here
ACLs do not inherently allow spoofing; spoofing depends on other factors.
✓
Risk of data exfiltration via DNS tunneling.
Why this is correct
Permissive DNS outbound can be exploited for covert data transfer.
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
The trap here is that candidates may focus on the firewall rule allowing outbound DNS traffic and incorrectly assume it only poses a risk of unauthorized external access (option A), overlooking the more subtle but critical risk of data exfiltration via DNS tunneling, which is a well-known covert channel in security assessments.
Detailed technical explanation
How to think about this question
DNS tunneling works by encoding data in the subdomain or TXT record fields of DNS queries, which are often not inspected deeply by firewalls. Tools like dnscat2 or Iodine can establish a command-and-control channel over DNS, bypassing network proxies and content filters. In real-world scenarios, attackers use this technique to exfiltrate data from air-gapped networks or to maintain persistence, as DNS traffic is rarely blocked entirely.
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.
Information Security Risk Management — This question tests Information Security Risk Management — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Risk of data exfiltration via DNS tunneling. — The exhibit shows a firewall rule that permits DNS traffic (UDP/TCP port 53) from the internal network to any external destination. This configuration allows internal hosts to perform DNS queries to external servers, which can be exploited for DNS tunneling—a technique where data is encapsulated within DNS queries and responses to bypass security controls and exfiltrate sensitive information. Since DNS traffic is typically allowed through firewalls, this creates a covert channel for data exfiltration, making option D the most likely risk.
What should I do if I get this CISM 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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Question Discussion
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