On August 13, 2025, the Cybersecurity and Infrastructure Security Agency (CISA), together with the National Security Agency (NSA), the Federal Bureau of Investigation (FBI), the Environmental Protection Agency (EPA) and several international partners, published detailed guidance aimed at helping operational technology (OT) owners and operators build, maintain, and operationalize robust OT asset inventories and supplemental taxonomies—a foundational step for securing critical infrastructure against increasingly persistent cyber threats.
Operational technology environments—industrial control systems, supervisory control and data acquisition (SCADA) systems, programmable logic controllers (PLCs), human-machine interfaces (HMIs) and supporting networks—are the backbone of energy, water, manufacturing, transportation and other critical sectors. In recent years, federal agencies and industry groups have repeatedly emphasized that knowing what you have is the essential first step in protecting it. The new cross-agency guidance expands on that premise by offering concrete recommendations for creating a regularly updated, structured asset inventory and a taxonomy that classifies assets by role, criticality and function.
The guidance is positioned as both prescriptive and practical: it describes the minimum attributes an OT asset inventory should capture, how to design a supplemental taxonomy to classify assets in operational terms, and how to use inventories and taxonomies to inform risk reduction, incident response, and procurement. It deliberately aligns with prior federal advisories that have urged immediate actions—like network mapping, inventory creation, and reducing internet exposure of OT devices—while attempting to translate those high-level directives into operational checklists and governance points that OT owners and operators can implement.
Key attributes to include:
Core governance elements:
Use the inventory to:
Recommended KPIs:
If an organization expects to rely on vendor-supplied discovery or replacement schedules, those claims and timelines should be verified contractually. Any claims about exact reduction in breach likelihood from implementing an inventory are inherently context-dependent and should be treated as directional rather than absolute.
Implementing the guidance requires an investment in people, process and technology, plus careful risk management to avoid disruption. Organizations that approach inventory as an ongoing capability—governed, integrated, and tied to operational outcomes—will be far better positioned to reduce downtime, protect safety, and defend critical services in an increasingly contested threat environment.
Source: CISA CISA and Partners Release Asset Inventory Guidance for Operational Technology Owners and Operators | CISA
Background
Operational technology environments—industrial control systems, supervisory control and data acquisition (SCADA) systems, programmable logic controllers (PLCs), human-machine interfaces (HMIs) and supporting networks—are the backbone of energy, water, manufacturing, transportation and other critical sectors. In recent years, federal agencies and industry groups have repeatedly emphasized that knowing what you have is the essential first step in protecting it. The new cross-agency guidance expands on that premise by offering concrete recommendations for creating a regularly updated, structured asset inventory and a taxonomy that classifies assets by role, criticality and function.The guidance is positioned as both prescriptive and practical: it describes the minimum attributes an OT asset inventory should capture, how to design a supplemental taxonomy to classify assets in operational terms, and how to use inventories and taxonomies to inform risk reduction, incident response, and procurement. It deliberately aligns with prior federal advisories that have urged immediate actions—like network mapping, inventory creation, and reducing internet exposure of OT devices—while attempting to translate those high-level directives into operational checklists and governance points that OT owners and operators can implement.
Why an OT asset inventory matters now
The rationale behind the guidance is straightforward but urgent. OT environments are being targeted more frequently by sophisticated actors who exploit unknown or unmanaged devices, internet-facing HMIs, and weak procurement practices. Without an up-to-date inventory and a coherent taxonomy:- Organizations cannot reliably map attack surface or prioritize remediation.
- Incident response is delayed because teams lack instant visibility into impacted process equipment.
- Procurement and vendor management remain reactive, allowing insecure devices into production.
- Regulatory and compliance obligations are harder to meet, increasing corporate and societal risk.
What the guidance recommends (high level)
The guidance frames an OT asset inventory as a structured, repeatable program with these core components:- A baseline inventory covering hardware, firmware, software, and process-controller artifacts.
- A supplemental taxonomy that categorizes assets by function, criticality to process, connectivity, and safety impact.
- Discovery techniques that combine passive and selective active methods to avoid disrupting control systems.
- A governance model tying inventory ownership to operations (OT) and security (cyber) stakeholders.
- Integration points: CMMS, configuration management databases (CMDBs), SIEM, vulnerability management tools, and incident response runbooks.
- Continuous maintenance, change control, and verification (including periodic physical walkdowns).
Anatomy of a useful OT asset inventory
A practical inventory goes well beyond listing IP addresses. The guidance recommends capturing both technical and operational attributes that make an asset actionable during daily ops and emergencies.Key attributes to include:
- Device identity: manufacturer, model, serial number, and vendor-supplied identifiers.
- Network attributes: IP/MAC address (if applicable), VLAN, physical port, and network zone.
- Software/firmware: installed versions, patch level, and known vulnerabilities.
- Process role: what the device controls or monitors (pump, valve, generator, HMI panel).
- Criticality classification: impact to safety, environment, mission, and continuity (tiered).
- Physical location and ownership: facility, cell/line, and responsible engineer or contractor.
- Maintenance and lifecycle: date of installation, expected end-of-support, replacement schedule.
- Remote access details: vendor access channels, remote sessions, VPN accounts, and remote service contracts.
- Dependencies and upstream/downstream relationships: which systems depend on this asset’s availability.
Example taxonomy axes
The supplemental taxonomy should be tailored to each organization's processes, but several commonly useful axes include:- Function (e.g., control, monitoring, safety, historian, gateway).
- Process criticality (e.g., safety-critical, production-critical, auxiliary).
- Network exposure (internet-facing, business-connected, air-gapped).
- Trust level (internal, vendor-managed, guest).
- Replacement difficulty (easy, moderate, complex).
Discovery: safe techniques for fragile environments
Discovery in OT must balance visibility with the imperative to avoid operational disruption. The guidance emphasizes a pragmatic combination of:- Passive network monitoring: traffic analysis using tools that do not inject packets into the control network. Passive methods reveal live communication patterns, protocol usage (Modbus, DNP3, OPC-UA, etc.), and unexpected or unauthorized talkers.
- Vendor-supplied tools and safe, controlled active scans: when active methods are necessary, use vendor-validated scanners and schedule scans during maintenance windows with operator oversight.
- Physical walkdowns and asset verification: nothing replaces physically verifying equipment, labels, and wiring, particularly for legacy and spare assets.
- Configuration and system artefacts: harvesting lists from historians, asset management systems, and programmable controller backups to supplement network-derived data.
- Service contracts and third-party inventories: cross-check vendor-provided equipment lists, remote access accounts, and support agreements.
Governance: who owns the inventory?
One of the guidance’s practical strengths is its emphasis on governance. Without clear ownership, inventories stagnate and lose trust. The recommended governance model assigns primary responsibility to OT operations but requires tight integration with cybersecurity teams and executive leadership.Core governance elements:
- A designated inventory owner (often an OT engineering lead) accountable for accuracy.
- A cross-functional steering committee with representatives from OT, cybersecurity, procurement, legal, and vendor management.
- Defined update cadences (e.g., continuous automated feeds plus quarterly audits and annual physical verification).
- Change-control integration so inventory updates are part of engineering change requests and maintenance tickets.
- Metrics for inventory health: percentage of assets with complete metadata, number of unknown devices detected, and timeliness of updates.
How inventories drive improved cybersecurity and resilience
An accurate inventory and taxonomy unlock a series of high-value security outcomes:- Prioritized vulnerability management: remediation resources can be focused on devices with the highest operational impact rather than on an ad hoc basis.
- Faster incident triage and containment: responders can rapidly identify affected process elements and isolate only the minimal network segments required to maintain safety.
- Better procurement and secure product selection: buyers can demand specific security capabilities from suppliers because they understand where products will sit in the topology and what their criticality is.
- Targeted segmentation and microsegmentation: segmentation plans become implementable when you know asset interdependencies and their communication patterns.
- Regulatory and compliance readiness: many sector-specific standards and regulator frameworks expect demonstrable asset awareness as part of audits.
Strengths and practical improvements in the guidance
The new guidance offers several notable strengths that make it practical and implementable:- Cross-agency collaboration: the joint release by CISA, NSA, FBI, EPA and partners signals unified federal priorities and provides operational credibility for owners and operators when engaging executive leadership or vendors.
- Operational focus: the guidance frames taxonomy and inventories in operational terms (process role, safety criticality), making them useful for control-room operators and incident commanders, not just CISOs.
- Actionable discovery techniques: realistic recommendations on passive monitoring and vendor-validated discovery reduce fear of damaging fragile control systems.
- Integration emphasis: by insisting that inventories feed CMDBs, CMMS, SIEMs and vulnerability management workflows, the guidance pushes organizations away from isolated spreadsheets toward automated ecosystems.
- Lifecycle orientation: capturing maintenance, firmware, and support end-of-life helps organizations plan replacements and avoid running unsupported critical equipment.
Risks, gaps, and implementation challenges
The guidance is sensible, but practical implementation can uncover significant risks and constraints that OT owners and operators must manage.- Operational disruption risk: even careful active discovery carries a non-zero risk of causing device resets or network instability. Organizations must maintain conservative testing windows and vendor coordination.
- Resource and skills gap: many OT teams lack dedicated cybersecurity staffing, and cybersecurity teams often lack OT domain expertise. Building cross-disciplinary teams requires hiring, training, and cultural change.
- Legacy and proprietary systems: older devices may lack identifiers or remote-queryable interfaces, making full inventorying technically hard without manufacturer involvement or manual verification.
- Vendor cooperation and procurement friction: manufacturers may resist exposing firmware or identifying embedded third-party components. Contractual, legal and commercial conversations can be slow.
- Data sensitivity and privacy: inventory data can contain sensitive facility and process information. Controls are needed to protect inventory stores from unauthorized access and to manage sharing with third parties.
- False sense of security: simply listing assets is insufficient; inventories must be accurate and continuously maintained. Stale inventories can be worse than none because they engender misplaced confidence.
- International applicability: the guidance references collaborations with international partners but does not specify harmonized taxonomies. Multinational operators will need to reconcile domestic guidance with local regulations and standards.
Practical, phased implementation roadmap
For OT owners and operators looking to adopt the guidance, a phased, risk-aware approach is essential.- Scoping and governance
- Identify organizational owners and sponsors.
- Create a cross-functional steering committee with clear roles.
- Baseline discovery (passive-first)
- Deploy passive network monitoring to build an initial map.
- Collect logs, historian entries and engineering documentation.
- Taxonomy design workshop
- Define taxonomy axes (function, criticality, exposure).
- Create machine-readable classification rules.
- Asset attribute definition
- Agree on required metadata fields and acceptable data sources.
- Controlled active validation
- Use vendor-approved tools and maintenance windows to validate passive findings.
- Integration and automation
- Feed inventory data into CMDB/CMMS/SIEM and vulnerability management tools.
- Establish automated reconciliation jobs and alerts for unknown devices.
- Continuous maintenance and audits
- Schedule quarterly reconciliations, annual physical verifications, and post-change updates.
- Use-case enablement
- Update incident response playbooks and segmentation plans using inventory data.
- Adjust procurement templates to require asset-class security features.
- Metrics and reporting
- Track completeness, age, and drift metrics; report to leadership.
- Vendor engagement and replacement planning
- Use inventory lifecycle fields to plan end-of-support replacements and procurement prioritization.
Tools and techniques to consider
The guidance calls for a mix of tools and techniques appropriate for OT constraints.- Passive packet capture and flow analysis tools that understand industrial protocols.
- OT-aware asset discovery platforms designed for control-system environments.
- CMMS and CMDB integration to link inventory data to maintenance and work-order processes.
- SIEM and SOAR integrations to enrich security telemetry with operational context.
- Vulnerability scanning tools built or configured for OT devices, used conservatively.
- Vendor-managed inventory feeds and contractual rights to manufacturer documentation.
Sector-specific considerations
Different critical infrastructure sectors will need to tailor implementation to their regulatory and operational realities.- Energy (including NERC CIP-regulated entities) should map inventory attributes to NERC CIP asset and cyber asset classifications and use taxonomy to inform critical facilities and BES responsibilities.
- Water and wastewater systems should emphasize HMIs, remote telemetry units, and process sensors that could directly impact public health and safety.
- Manufacturing and discrete industries should focus on production-line segmentation, spare-parts inventories, and safety instrumented systems (SIS).
- Transportation and logistics operators should prioritize control systems that affect vehicle safety and signaling.
Procurement and supplier engagement: using the inventory as leverage
A practical dividend from a rigorous inventory is improved procurement leverage. When buyers can clearly state where a device will be deployed, what its exposure will be, and what lifecycle is required, vendor responses become more measurable.Use the inventory to:
- Create procurement questionnaires requiring baseline security features (secure boot, update mechanisms, logging).
- Demand transparency about third-party components and supply-chain provenance.
- Define minimum support windows and patch commitments in contracts.
- Make procurement conditional on vendor-provided secure configuration guides and test evidence.
Measuring success: KPIs for an OT inventory program
Meaningful metrics help sustain the program and demonstrate value.Recommended KPIs:
- Percentage of OT assets with complete metadata.
- Mean Time to Identify (MTTI) for previously unknown OT devices.
- Percentage of internet-exposed OT assets reduced over a defined period.
- Percentage of operationally critical devices with up-to-date firmware or mitigations.
- Time from detection of an incident to identification of affected assets.
- Number of procurement contracts updated to include security requirements.
Cautions and unverifiable elements
Certain statements in early summaries of the guidance reference “several international partners” without enumerating them publicly; operators should treat the exact partner list as a policy-level detail that may be published separately. Additionally, while the guidance prescribes taxonomy axes and attributes, optimal field names and exact priority thresholds will vary by organization and sector; there is no one-size-fits-all taxonomy that guarantees compliance across all regulatory environments.If an organization expects to rely on vendor-supplied discovery or replacement schedules, those claims and timelines should be verified contractually. Any claims about exact reduction in breach likelihood from implementing an inventory are inherently context-dependent and should be treated as directional rather than absolute.
Bottom line: inventory as infrastructure
The new CISA-led guidance refocuses a long-standing cybersecurity truth for the industrial era: visibility is the indispensable foundation of security and resilience. For OT owners and operators, an operationally oriented asset inventory and a practical taxonomy are not simply compliance checkboxes; they are mission-critical infrastructure that enables prioritized risk reduction, reliable incident response, secure procurement, and cross-functional coordination.Implementing the guidance requires an investment in people, process and technology, plus careful risk management to avoid disruption. Organizations that approach inventory as an ongoing capability—governed, integrated, and tied to operational outcomes—will be far better positioned to reduce downtime, protect safety, and defend critical services in an increasingly contested threat environment.
Action checklist for OT owners and operators (quick-reference)
- Establish governance: assign an inventory owner and create a cross-functional steering group.
- Start passive discovery immediately; avoid uncontrolled active scans.
- Define a supplemental taxonomy that maps to process function and criticality.
- Record both technical and operational attributes for each asset.
- Integrate the inventory with CMDB/CMMS, vulnerability management and incident response tools.
- Schedule periodic physical verifications and reconcile vendor lists.
- Update procurement templates to require security features and vendor transparency.
- Track and publish inventory health KPIs to executive leadership.
- Plan for legacy device replacement where remediation is not feasible.
Source: CISA CISA and Partners Release Asset Inventory Guidance for Operational Technology Owners and Operators | CISA
