Which of the following is a commonly used SIEM tool?

Splunk is widely recognized as a commonly used Security Information and Event Management (SIEM) tool. It is designed to collect, analyze, and visualize machine-generated data from various sources, such as logs, which is essential for monitoring and responding to security incidents. Splunk enables organizations to gain insights from their data in real-time, helping security teams to detect anomalies, investigate threats, and maintain compliance with regulatory standards.

In contrast, Wireshark is primarily a network protocol analyzer used for capturing and inspecting packet data on networks, making it more suitable for network troubleshooting than for comprehensive security event management. Nessus is a vulnerability scanner that focuses on identifying vulnerabilities in systems and networks rather than providing SIEM capabilities. Metasploit is a penetration testing framework used to exploit vulnerabilities in systems and applications; it is not designed for log management or security monitoring like SIEM tools. Therefore, Splunk stands out as the fitting choice for a SIEM solution in the given options.