The U.S. Cybersecurity and Infrastructure Security Agency (CISA) and partners published on Wednesday a resource that helps OT (operational technology) system owners and operators strengthen infrastructure security by creating a clear inventory and classification of their assets. By effectively identifying, organizing, and managing OT assets, organizations can enhance cybersecurity while improving operational reliability, safety, and resilience. Across the existing industrial landscape, OT systems are no longer isolated islands, but are deeply integrated with IT and business networks, making them prime targets for cyberattacks. Recognizing this growing risk, the document guides organizations to mitigate vulnerabilities and protect critical operations.
Titled ‘Foundations for OT Cybersecurity: Asset Inventory Guidance for Owners and Operators,’ the resource outlines a process for OT owners and operators to create an asset inventory and OT taxonomy. This process includes defining the scope and objectives for the inventory, identifying assets, collecting attributes, creating a taxonomy, managing data, and implementing asset life cycle management. These steps define a thorough and systematic approach to creating and maintaining an OT asset inventory
and OT taxonomy, enabling organizations to maintain an accurate and up-to-date record of their OT assets.
Furthermore, this guidance outlines how OT owners and operators can maintain, improve, and use their asset inventory to protect their most vital assets. Steps include OT cybersecurity and risk management, maintenance and reliability, performance monitoring and reporting, training and awareness, and continuous improvement. By addressing these areas, organizations can enhance their overall security posture and ensure the reliability and safety of their OT environments.
“Having a complete and accurate OT asset inventory is the essential first step toward building a defensible architecture and more resilient operations,” Clayton Romans, associate director for the Joint Cyber Defense Collaborative (JCDC), wrote in a Wednesday blog post. “CISA’s guidance makes that complex process clear and achievable, empowering organizations to take decisive action.”
More than just a technical manual, Romans said that this guidance serves as a strategic enabler for cyber defense actions and operational collaboration with CISA and other key stakeholders. “With a precise understanding of the assets within an operator’s infrastructure, Common Vulnerabilities and Exposures (CVEs) added to CISA’s Known Exploited Vulnerabilities Catalog or to stakeholder notifications and threat advisories become significantly more actionable and timely—helping operators reduce risk proactively, before incidents escalate.”
“To support this effort, CISA offers tools and resources, including MALCOLM for network traffic analysis, no-cost Cyber Hygiene vulnerability scanning, Cyber Security Evaluation Tool (CSET), and cross-agency support to help validate and manage asset data,” Romans added. “Additionally, CISA provides support through regional Protective Security Advisors (PSAs), Cyber Security Advisors (CSAs), Emergency Communications Coordinators (ECCs), and Chemical Security Inspectors (CSIs).”
Developed through the JCDC, the asset inventory guidance was created by CISA in collaboration with the Environmental Protection Agency (EPA), the National Security Agency (NSA), the Federal Bureau of Investigation (FBI), Australia’s Signals Directorate’s Australian Cyber Security Centre (ASD’s ACSC), the Canadian Centre for Cyber Security (Cyber Centre), Germany’s Federal Office for Information Security (BSI), the Netherlands’ National Cyber Security Centre (NCSC-NL), and New Zealand’s National Cyber Security Centre (NCSC-NZ).
Creating an asset inventory is necessary for building a modern defensible architecture and is one of CISA’s Cybersecurity Performance Goals (CPGs). A modern defensible architecture mitigates risk through a thoughtful system design and implementation that enables OT cyber defenders to identify, prevent, and respond to cyber threats while ensuring reliability, operational continuity, safety, and compliance with regulatory requirements.
An OT asset inventory typically consists of an organized, regularly updated list of an organization’s OT systems, hardware, and software. It is foundational to designing a modern defensible architecture because, without an inventory, organizations do not know what they have and what should be secured and protected.
The real value of an OT asset inventory comes when it is fully integrated into daily operations. With an inventory in place, operators can prioritize vulnerabilities based on criticality and exposure, detect unauthorized devices before they become attack vectors, support network segmentation efforts by mapping communication flows, and enable incident response teams to act quickly and accurately.
Developing an asset inventory is a multi-step process where OT owners and operators identify, classify, and document assets. OT owners and operators who develop an OT taxonomy as part of the inventory process can significantly enhance the process. An OT taxonomy is a categorization system used to organize and prioritize OT assets to facilitate risk identification, vulnerability management, and incident response. The taxonomy aids owners and operators in conducting asset inventories by facilitating classification of assets by function and/or criticality and visualizing asset relationships and dependencies.
The asset inventory guidance outlines key actions OT owners and operators should take with their inventory. Owners and operators should identify known vulnerabilities, available patches, updates, and hardening guidance for vendor systems and applications. They should cross-reference their inventories with established vulnerability databases, such as CISA’s Known Exploited Vulnerabilities (KEV) Catalog, which highlights actively exploited vulnerabilities, and MITRE’s Common Vulnerabilities and Exposures (CVE) database, which provides detailed reports on identified security flaws.
Security controls should be continuously explored for vendor systems and applications with known OT vulnerabilities that cannot be patched immediately or are end-of-life. Critical assets and systems should be prioritized, with detailed redundancy plans and the ability to operate under compromise if these assets are targeted. Real-time monitoring should be implemented to detect emerging threats and vulnerabilities. The KEV catalog should be used as authoritative input to a vulnerability management prioritization framework.
Moreover, organizations may also use frameworks such as the Stakeholder-Specific Vulnerability Categorization (SSVC) model, which considers a vulnerability’s exploitation status, and employ automated vulnerability and patch management tools that flag or prioritize KEV vulnerabilities.
The asset inventory guidance identified that threat factors should be prioritized by mapping potential attack patterns to known threat intelligence sources, including the MITRE ATT&CK Matrix for ICS and MITRE’s Common Attack Pattern Enumeration and Classification (CAPEC) for Industrial Control System Patterns. Security efforts should focus on the most critical risks and be strengthened by designing a security architecture that incorporates effective controls, such as segmentation, access management, and monitoring.
Maintenance plans should be reviewed with consideration of vulnerability assessment findings and mitigations. Mitigating actions or patching should be scheduled during maintenance windows unless urgency requires an emergency change. The costs of potential downtime or degraded services should be weighed against the cost of replacing vulnerable systems or deploying compensating controls. More secure systems should be implemented using cyber-informed engineering principles and secure-by-design guidance to embed security into procurement and engineering decisions. Taxonomy and risk management processes should inform these security decisions. OT spare parts inventories should be analyzed to ensure stockpiles sufficiently cover critical assets and maintain operational reliability.
Asset performance and status should be continuously monitored, with process variable monitoring focused on real-time indicators such as temperature, pressure, and flow to detect performance issues or maintenance needs. Network and system diagnostics monitoring should leverage continuous monitoring tools to analyze communication health, device connectivity, and process flow integrity. Reporting mechanisms should be developed to track asset performance, maintenance activities, and compliance with policies. Asset inventory owners should be identified to oversee updates and validate classifications to ensure ongoing accuracy, maintenance, and reporting.
The asset inventory guidance also called for staff to be trained in asset management practices, tools, and procedures, and awareness programs should be implemented to ensure all stakeholders understand the importance of asset management. Continuous improvement should be fostered through feedback loops to gather insights from asset management activities and identify areas for improvement. Change management processes should be used to track OT asset modifications, additions, and decommissioning accurately. Regular reviews of the inventory and audits of the asset management program should be conducted to ensure the program remains effective and aligned with organizational goals.
Last month, global cybersecurity agencies published new guidance to help OT owners and operators across critical infrastructure sectors create and maintain comprehensive OT asset inventories and taxonomies. The document outlines the process to create an OT asset inventory, develop a taxonomy of OT systems, and create a modern defensible architecture by providing net defenders with digestible foundational elements and best practices. This is critical as OT systems are vital to the core functionality of the nation’s critical infrastructure to safely and reliably operate by powering process automation, instrumentation, cyber-physical operations, and ICS (industrial control systems).
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