CS0-003 Incident Response and Management Practice Question
This CS0-003 practice question tests your understanding of incident response and management. Compare every option against the stated constraints before choosing — the best answer satisfies all requirements, not just the most obvious one. 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.
A security analyst notices that a system is sending a large amount of data to an external IP address via DNS tunneling. Which containment technique is most appropriate?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Disconnect the system from the network
Disconnecting the system from the network (Option B) is the most appropriate containment technique because it immediately stops all data exfiltration, including DNS tunneling traffic, without relying on any other network component. DNS tunneling works by encoding data within DNS queries and responses, so simply changing DNS server settings or blocking the external IP may not stop the attack if the malware uses fallback resolvers or rotates IPs. Disconnecting the system ensures the threat is isolated at the host level, preventing further data loss while preserving forensic evidence.
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.
✗
Change the DNS server settings
Why it's wrong here
Changing DNS settings may not stop the tunneling if the attacker uses custom resolvers.
✓
Disconnect the system from the network
Why this is correct
Immediate isolation prevents any further data exfiltration.
Related concept
Read the scenario before looking for a memorised answer.
✗
Block the external IP at the firewall
Why it's wrong here
Blocking IP may stop traffic but does not isolate the system if it uses other IPs.
✗
Disable the DNS service on the system
Why it's wrong here
Disabling DNS may disrupt system functionality and does not stop tunneling if other protocols are used.
Common exam traps
Common exam trap: answer the scenario, not the keyword
CompTIA often tests the principle that containment must be immediate and host-level for active data exfiltration, and the trap here is that candidates choose firewall-based blocking (Option C) thinking it stops the traffic, but fail to realize the attacker can easily change IPs or use multiple resolvers, making host isolation the only sure containment.
Detailed technical explanation
How to think about this question
DNS tunneling exploits the fact that DNS queries and responses are often allowed through firewalls without deep inspection. Tools like dnscat2 or Iodine encode data in subdomain labels or TXT record responses, using base32/base64 encoding to bypass size limits. In a real-world scenario, an attacker might use a compromised system to exfiltrate sensitive data over months by blending with normal DNS traffic, making detection difficult without specialized DNS logging or machine learning anomaly detection.
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 CS0-003 question in full detail.
Incident Response and Management — This question tests Incident Response and Management — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Disconnect the system from the network — Disconnecting the system from the network (Option B) is the most appropriate containment technique because it immediately stops all data exfiltration, including DNS tunneling traffic, without relying on any other network component. DNS tunneling works by encoding data within DNS queries and responses, so simply changing DNS server settings or blocking the external IP may not stop the attack if the malware uses fallback resolvers or rotates IPs. Disconnecting the system ensures the threat is isolated at the host level, preventing further data loss while preserving forensic evidence.
What should I do if I get this CS0-003 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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Question Discussion
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