This paper investigates the enforcement of state-based security properties in process systems through supervisory control. We introduce a supervisor that operates under the assumption of incomplete system knowledge, mirroring the challenges faced in real-world deployments where both the supervisor and potential adversaries possess limited information. The proposed supervisor rectifies insecure process behaviors by strategically restricting actions or injecting timed events. Our study focuses on analyzing the necessary and sufficient conditions for the existence of such a supervisor capable of guaranteeing process security despite the knowledge limitations.