CMMC Practice SI.2.217
Identify unauthorized use of organizational systems.
Bold Coast Security Guidance
Your organization should create an Acceptable Use policy which is given to all users at hire, and then again annually. A good time to have the users review it is during the annual security training, or during staff performance reviews.
One you have determined the authorized use of your systems and created a policy, your plan should include review of IDS/IPS logs, anti-virus logs, violations of your web filters policies, and activity flagged by your SIEM. You should also create alerts and specific notifications for indicators of unauthorized use, such as creation of new accounts, large numbers of failed login attempts, changes to firewall configurations.
DRAFT NIST SP 800-171 R2
System monitoring includes external and internal monitoring. System monitoring can detect unauthorized use of organizational systems. System monitoring is an integral part of continuous monitoring and incident response programs. Monitoring is achieved through a variety of tools and techniques (e.g., intrusion detection systems, intrusion prevention systems, malicious code protection software, scanning tools, audit record monitoring software, network monitoring software). Output from system monitoring serves as input to continuous monitoring and incident response programs.
Unusual/unauthorized activities or conditions related to inbound and outbound
communications traffic include internal traffic that indicates the presence of malicious code in systems or propagating among system components, the unauthorized exporting of information, or signaling to external systems. Evidence of malicious code is used to identify potentially compromised systems or system components. System monitoring requirements, including the need for specific types of system monitoring, may be referenced in other requirements.
NIST SP 800-94 provides guidance on intrusion detection and prevention systems.