- A
Block all outbound DNS traffic from the server immediately.
Why wrong: Blocking all DNS traffic may prevent legitimate services that rely on name resolution, and it does not address the underlying compromise. Attackers could also use alternative exfiltration methods. This action is too broad and does not follow the containment-first principle.
- B
Isolate the server from the network to prevent further data loss.
Isolation effectively stops the ongoing DNS tunneling by severing the server’s network connectivity. This contains the incident, prevents additional data exfiltration, and provides a controlled environment for further forensic analysis. It aligns with standard incident response procedures.
- C
Create a firewall rule to log all further DNS queries from the server.
Why wrong: Logging is a detection and monitoring technique, but it does not stop the active exfiltration. The analyst already knows the server is compromised; enabling logging without containment allows data loss to continue. This is a step better suited after containment.
- D
Run an antivirus scan on the server.
Why wrong: Antivirus scans may detect known malware, but DNS tunneling tools are often custom or fileless and may bypass traditional signatures. Moreover, scanning is a lengthy process that does not immediately halt the exfiltration. Containment should come before remediation.
Quick Answer
The correct immediate action is to isolate the server from the network to prevent further data loss. This is because the unusual DNS queries containing encoded subdomain names are a classic sign of DNS data exfiltration, where an attacker tunnels stolen data out through DNS requests. Since the server is not a DNS server and is generating unexpected outbound traffic, the priority is to stop the active data theft before it continues. On the Security+ SY0-701 exam, this scenario tests your understanding of incident response priorities—specifically that containment (isolation) comes before eradication or recovery. A common trap is choosing to block the DNS traffic or scan the server, but those actions do not halt the exfiltration in progress and may alert the attacker. Remember the memory tip: “DNS Dump—Isolate First” to emphasize that stopping the data leak is the immediate goal.
SY0-701 Security Operations Practice Question
This SY0-701 practice question tests your understanding of security operations. 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 at a financial firm notices a significant increase in DNS queries from an internal server to a rarely visited external domain. The queries are for unusual subdomain names that contain encoded data. The server is not a DNS server and does not typically generate outbound traffic. Which of the following is the MOST appropriate immediate action for the analyst to take?
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
Isolate the server from the network to prevent further data loss.
The server is exhibiting signs of a DNS data exfiltration attack, where encoded data is being tunneled through DNS queries to an external domain. Isolating the server immediately stops the data loss and prevents further compromise, which is the most critical first step in incident response. Blocking traffic or scanning alone would not halt the active exfiltration, and logging without action allows continued data theft.
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.
- ✗
Block all outbound DNS traffic from the server immediately.
Why it's wrong here
Blocking all DNS traffic may prevent legitimate services that rely on name resolution, and it does not address the underlying compromise. Attackers could also use alternative exfiltration methods. This action is too broad and does not follow the containment-first principle.
- ✓
Isolate the server from the network to prevent further data loss.
Why this is correct
Isolation effectively stops the ongoing DNS tunneling by severing the server’s network connectivity. This contains the incident, prevents additional data exfiltration, and provides a controlled environment for further forensic analysis. It aligns with standard incident response procedures.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
Create a firewall rule to log all further DNS queries from the server.
Why it's wrong here
Logging is a detection and monitoring technique, but it does not stop the active exfiltration. The analyst already knows the server is compromised; enabling logging without containment allows data loss to continue. This is a step better suited after containment.
- ✗
Run an antivirus scan on the server.
Why it's wrong here
Antivirus scans may detect known malware, but DNS tunneling tools are often custom or fileless and may bypass traditional signatures. Moreover, scanning is a lengthy process that does not immediately halt the exfiltration. Containment should come before remediation.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates choose to log or scan first, mistaking detection for containment, but the SY0-701 emphasizes immediate isolation to stop data loss in active exfiltration scenarios.
Detailed technical explanation
How to think about this question
DNS exfiltration exploits the fact that DNS queries are often allowed through firewalls; the attacker encodes stolen data into subdomain labels (e.g., base64-encoded chunks) of a controlled domain. The server's DNS resolver sends these queries to the attacker's authoritative nameserver, which logs the subdomains to reconstruct the data. Isolating the server (e.g., disconnecting its network cable or placing it in a quarantine VLAN) stops the exfiltration at the network layer, preserving forensic evidence for later 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 security team runs a vulnerability scan on a web application and discovers an unpatched SQL injection flaw. The team prioritises remediation by CVSS score — critical flaws are patched within 24 hours, high within 7 days. Questions like this test whether you understand vulnerability management processes, scanning tools, and remediation prioritisation.
What to study next
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FAQ
Questions learners often ask
What does this SY0-701 question test?
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: Isolate the server from the network to prevent further data loss. — The server is exhibiting signs of a DNS data exfiltration attack, where encoded data is being tunneled through DNS queries to an external domain. Isolating the server immediately stops the data loss and prevents further compromise, which is the most critical first step in incident response. Blocking traffic or scanning alone would not halt the active exfiltration, and logging without action allows continued data theft.
What should I do if I get this SY0-701 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.
About these practice questions
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Last reviewed: Jun 11, 2026
This SY0-701 practice question is part of Courseiva's free CompTIA certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the SY0-701 exam.
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