Company ABC has employed a firewall, IDS, Antivirus, Domain Controller, and SIEM. The company’s domain controller goes down. From which system would you begin your investigation?

A Security Information and Event Management (SIEM) system is the most logical starting point for an investigation. The primary function of a SIEM is to aggregate, correlate, and analyze log data from multiple sources across the network, including the firewall, IDS, and the Domain Controller itself. Since the Domain Controller is down, its local logs may be inaccessible. The SIEM provides a centralized, historical view of all relevant events leading up to the failure. An analyst can use the SIEM to review time-correlated data for system errors, security alerts from the IDS, anomalous traffic patterns from the firewall, and other indicators that could reveal the root cause of the outage.

A. Domain Controller: The system is down, making it an impractical starting point. Even if its logs were accessible, they would lack the crucial correlated context from other network devices.
B. Firewall: This provides only a narrow view of network traffic. The cause of the failure might not be network-related, making this an inefficient starting point.
D. IDS: This system only reports on potential security intrusions. The Domain Controller could have failed due to hardware issues, misconfiguration, or software errors not detected by an IDS.

1. National Institute of Standards and Technology (NIST) Special Publication 800-92, Guide to Computer Security Log Management. Section 2.3, "Log Management Infrastructures," describes the benefits of a centralized logging architecture, stating, "Centralized log servers also facilitate the log analysis process by providing a single location for logs." Section 4.3, "Log Analysis," further explains that logs are used for "reconstructing the steps of an event" and "troubleshooting." This supports using the central log repository (the SIEM) as the starting point for reconstructing the event of the DC failure.

2. Carnegie Mellon University, Software Engineering Institute (SEI). "Best Practices for Security Information and Event Management (SIEM)." This document outlines the core capabilities of a SIEM, including "Consolidation and correlation of data from multiple sources" and "Forensics and incident response." It emphasizes that a SIEM's ability to provide a unified view is critical for effective incident investigation, which is precisely the task required when the Domain Controller goes down. (Reference: CERT/SEI publications on SOC and SIEM best practices).

3. University of California, Berkeley. "Security 161: Computer Security, Lecture 19: Network Security Monitoring." Course materials often describe the security operations workflow where the SIEM is the primary tool for initial triage and investigation. It serves as the "single pane of glass" to review alerts and logs from disparate systems to form an initial hypothesis about an incident, such as a critical server outage.