The correct answer is D because the analyst should first validate whether the suspicious DNS domains are malicious or legitimate. Random-looking DNS domains may indicate malware using a domain generation algorithm (DGA) for command-and-control, but they can also appear in legitimate services such as content delivery networks or software update mechanisms. Therefore, the best first step is to enrich the DNS indicators using threat intelligence and reputation sources.
Exact supporting extract: the CySA+ All-in-One guide explains that DNS tunneling and abnormal DNS queries may be used for command-and-control or exfiltration. It also states that high-entropy domains appear random or “gibberish” to humans and that malware may use DGAs for C2 communication. However, it also warns that computer-generated domain names can have legitimate uses in content delivery networks.
The same guide explains that threat research should help answer questions such as whether an artifact is benign, whether anyone has seen it before, and why it is present in the system. It further explains that reputation data for domains, URLs, and IP addresses helps determine whether activity is associated with malware, phishing, C2, or data exfiltration.
Why the other options are incorrect:
A is incorrect because allowing the domains without validation could permit C2 or data exfiltration.
B is incorrect because reinstalling the software does not determine whether the DNS activity is malicious.
C is incorrect because blocking all outbound connections is a containment action, not the best first investigative step when the analyst is still determining whether compromise occurred.
D is correct because threat intelligence/reputation lookup is the most appropriate first validation step for suspicious DNS indicators.
