The behavior described is most consistent with an unauthenticated scan. In CEH-aligned vulnerability assessment methodology, unauthenticated scanning evaluates systems from the perspective of an external or non-privileged entity. The scanner can typically identify network-reachable services, open ports, service banners, protocol fingerprints, and sometimes known vulnerabilities inferred from versions or exposed configurations. However, it cannot reliably inspect host-internal posture such as registry settings, local security policies, installed patch levels, missing hotfixes, detailed configuration baselines, or user and group policy settings because those require authenticated access to query the operating system and installed software inventory directly.

The prompt explicitly states that the results were limited to “open service ports and version banners” and that “deeper registry settings, user policies, and missing patches remain unreported.” That limitation is a hallmark of unauthenticated scanning. The additional clue that “system login prompts were never triggered” and “no credential failures were logged in the SIEM” further confirms that the scanner never attempted to authenticate to endpoints using accounts, SSH/WinRM/WMI, SMB, or agent-based credential checks. If the scan were authenticated or credentialed, you would expect authentication attempts, potential login prompts on some services, and often audit logs or SIEM events reflecting successful or failed logons.

Option C, internal scan, only describes where the scan originates, not whether credentials were used. Options B and D imply authentication and host-level interrogation, which contradicts the observed lack of credential activity and missing patch/policy visibility. Therefore, unauthenticated scanning best explains the outcome.