This detection rule monitors for the registration of self-hosted GitHub Actions runners using the 'Runner.Listener' binary. When a machine is registered with a GitHub repository, it can execute arbitrary commands specified in workflows, potentially allowing malicious actors to perform unauthorized actions, leading to environments susceptible to remote code execution. The rule uses EQL (Event Query Language) to identify process start events where 'Runner.Listener' is initiated with specific arguments ('configure', '--url', and '--token'). If unauthorized registrations are detected, this could signal adversarial activities aimed at exploiting workflows for malicious purposes. Recommended investigation steps include checking the remote repository's trustworthiness, inspecting workflows for suspicious commands, analyzing process execution contexts, and correlating detected activities with other alerts to assess the potential for a supply chain attack.