Explanation
A false positive is a result that indicates a problem when there is no actual problem. In this case, the vulnerability scan flagged the domain controller with a critical vulnerability, but the domain controller does not run the application that is vulnerable. Therefore, the scan result is inaccurate and should be documented as a false positive.
A: Ensure the scan engine is configured correctly. This is not the next step, because the scan engine may be configured correctly and still produce false positives due to various factors, such as outdated signatures, network latency, or misconfigured devices.
B: Apply a patch to the domain controller. This is not the next step, because applying a patch to a system that does not have the vulnerability may cause unnecessary problems or conflicts.
C: Research the CVE. This is not the next step, because the systems administrator already researched the vulnerability and discovered that it does not affect the domain controller.
D: Document this as a false positive. This is the correct answer, because documenting false positives helps to improve the accuracy and efficiency of future scans and audits.
Reference: CompTIA Security+ Study Guide (PDF) - Netwrix, page 14.