Upon discovering that stolen credentials were used to run a remote command on the domain controller, what should be the immediate response action?

The most appropriate immediate response action in this scenario is to examine the specifics of the remote command executed. Understanding the details of the command is crucial for assessing the extent of the compromise and identifying any potential damage caused by the unauthorized access. Analyzing the command allows security analysts to gather intelligence on the attacker's intentions, such as whether they were attempting to exfiltrate data, escalate privileges, or manipulate settings on the domain controller. This understanding forms the foundation for subsequent actions, such as damage assessment, containment strategies, and recovery plans.

In an incident response scenario, prioritizing actions that improve situational awareness is vital. This enables teams to make informed decisions about how to proceed and what additional measures might be necessary to secure the environment. For example, knowing what commands were executed can also inform the decisions about which logs to review and other systems that may have been affected.

While locking down network access, increasing logging levels, and rebooting the domain controller are important considerations in a broader incident response strategy, these actions might not provide immediate clarity on the nature and impact of the breach, thereby prolonging the investigation and response. Hence, examining the specifics of the remote command executed takes precedence as it supplies critical context for further operational responses.