8 Practical Ways to Implement Zero Trust in Factories

The assumption that a factory is safe because its network is physically isolated from the internet has not been valid for years. Remote maintenance connections, supplier integrations, wireless sensor networks, and IT/OT convergence projects have collectively dismantled the perimeter that industrial security once depended on. Ransomware incidents affecting automotive plants, water utilities, and food manufacturers have confirmed what OT security professionals have long argued: in a connected factory, implicit trust is a liability.

Zero Trust is the architectural response. The principle is simple and uncompromising, no user, device, or system is trusted by default, regardless of whether it sits inside or outside the network boundary. Every access request is verified. Every connection is validated. Every session is monitored. Applied correctly in a factory context, Zero Trust reduces the blast radius of a compromise, limits lateral movement, and gives security teams the visibility they need to detect and respond before an incident becomes an outage.

The 8 Practical Ways to Implement Zero Trust in Factories in this article are designed for the operational reality of industrial environments: legacy equipment, uptime requirements, vendor dependencies, and the engineering culture that prioritizes availability above all else.

“Implementing Zero Trust in phases gave us visibility we simply did not have before, we found three unauthorized remote access paths in the first month.”, OT Security Lead, tier-1 automotive supplier (illustrative placeholder)

Why Perimeter Security Is No Longer Enough

Traditional industrial network security was built on a fortress model: strong walls, a controlled gate, and an assumption that everything inside was trustworthy. That model was functional when factories were genuinely isolated, air-gapped from corporate networks and the internet, with physical access as the primary control.

That world no longer exists for most manufacturers.

Today’s factories run historian servers that synchronize with cloud analytics platforms. Engineering workstations receive remote support from OEM vendors via VPN connections that may or may not be monitored. SCADA systems share network segments with IT infrastructure that was connected during a digital transformation project and never fully separated. Industrial Internet of Things (IIoT) sensors communicate over wireless protocols that were not designed with authentication in mind.

The attack surface in a modern factory is not a point, it is a distributed, dynamic, and constantly expanding landscape. The perimeter model cannot protect a landscape it cannot define.

Zero Trust does not replace every existing control. It supplements and structures them, shifting the security assumption from “trusted by default inside the network” to “verified and monitored regardless of location.” For factories, this is not an IT transformation. It is an operational risk management decision.

Relevant standards: IEC 62443 provides a widely adopted framework for industrial cybersecurity including zone-and-conduit segmentation that aligns naturally with Zero Trust principles. NIST SP 800-207 defines Zero Trust architecture for federal systems but is widely referenced in critical infrastructure [check source for current edition]. CISA’s Zero Trust Maturity Model provides a practical adoption roadmap applicable to OT environments.

Way 1 – Build an Accurate Asset Inventory First

What it means in a factory context: Zero Trust cannot protect assets you do not know exist. Before any segmentation, access control, or monitoring initiative, the foundational requirement is a complete, current, and continuously maintained inventory of every device on the OT network, PLCs, HMIs, engineering workstations, historians, RTUs, sensors, and network infrastructure.

Why it matters: Unknown assets are unmonitored, unpatched, and effectively invisible to your security posture. In many brownfield environments, network scans reveal devices that were installed during commissioning projects years ago and have never been formally documented.

Implementation guidance:

• Deploy passive discovery tools via SPAN ports or network TAPs, active scanning carries availability risk in OT environments and should only be used after careful validation in a lab or test environment
• Cross-reference discovered assets against your CMDB, maintenance records, and vendor documentation
• Capture: IP address, MAC address, device type, firmware version, communication protocols, and zone placement
• Assign each asset a criticality classification that will inform later segmentation and access control decisions

Realistic example: A plastics manufacturer conducting a passive discovery exercise found 14 undocumented PLCs and 6 legacy HMIs that had never appeared in any asset register. Three were running end-of-life firmware with known vulnerabilities. None were monitored.

Operational benefit: An accurate asset inventory reduces mean time to respond to incidents and provides the baseline required for every subsequent Zero Trust control.

Common blocker: Legacy OT devices that do not respond to standard discovery protocols. Compensate with physical walk-downs, maintenance record audits, and network traffic analysis to infer presence.

Way 2 – Segment OT Networks by Zones and Conduits

What it means in a factory context: Network segmentation divides the factory network into defined security zones, groups of assets with similar trust levels and communication requirements, separated by enforced conduits that control which traffic is permitted to cross boundaries.

Why it matters: Without segmentation, a compromised engineering workstation has potential network reachability to every PLC on the floor. Segmentation limits lateral movement, containing an incident to the zone where it originated rather than allowing it to propagate across the facility.

Implementation guidance:

• Apply the IEC 62443-3-2 zone-and-conduit model as a structural framework, define zones based on criticality, function, and required communication flows
• Implement deny-by-default policy at zone boundaries, only explicitly documented flows are permitted
• Deploy industrial-aware firewalls at zone boundaries that understand OT protocols (Modbus, DNP3, EtherNet/IP) rather than standard IT firewalls that cannot inspect industrial protocol commands
• For legacy devices that cannot be segmented at the network level, apply physical access controls and compensating monitoring

Realistic example: A food and beverage plant separated its production line PLC network from its quality management SCADA system using an OT DMZ with explicit allow-list rules. A subsequent ransomware incident originating on the corporate IT network was contained at the IT/OT boundary, production was unaffected.

Operational benefit: Segmentation reduces the blast radius of any incident and is one of the highest-impact controls available in brownfield environments.

OT-safe verification: Validate segmentation rules using passive traffic analysis before enforcing, identify any legitimate communication flows that would be blocked before applying deny-by-default policy.

Way 3 – Enforce Identity-Based Access for People and Machines

What it means in a factory context: Identity-based access control means that every connection to an OT asset is associated with a verified, authenticated identity, whether that identity belongs to a human engineer, a vendor technician, or an automated machine process.

Why it matters: Shared credentials, generic service accounts, and unauthenticated device communications are among the most consistently exploited vulnerabilities in OT environments. If any actor with network access can communicate with a PLC without authentication, network segmentation alone is insufficient.

Implementation guidance:

• Eliminate shared “admin” accounts on HMIs, engineering workstations, and SCADA systems, replace with individual named accounts
• Implement role-based access control (RBAC) aligned to job function, operators, engineers, and vendors each require different access scope
• For machine-to-machine communication, implement device identity using certificates or hardware-rooted credentials where the device supports it
• For legacy devices that cannot support modern authentication, compensate with network-layer controls and strict physical access policies

Realistic example: An automotive stamping plant replaced shared engineering workstation credentials with individual named accounts and discovered that three former contractors still had active login credentials, none of which had been used operationally for over a year.

Operational benefit: Named account accountability enables forensic attribution, when an incident occurs, you can determine which identity performed which action.

Way 4 – Use Least Privilege for Users, Vendors, and Service Accounts

What it means in a factory context: Least privilege means every user, vendor technician, and automated service account has access only to the specific assets and functions required for their defined role, nothing more.

Why it matters: Over-privileged accounts are a multiplier for any compromise. A vendor technician with broad network access who is the victim of a phishing attack becomes an entry point to every asset their credentials can reach.

Implementation guidance:

• Audit all existing user and service account privileges, identify accounts with more access than their role requires
• Implement time-limited access for vendors and contractors, credentials should be provisioned for the duration of a specific maintenance window and revoked automatically at the end
• Deploy a privileged access management (PAM) platform for all remote access to OT assets, this provides session logging, just-in-time provisioning, and automatic revocation
• Review and recertify all access rights quarterly

Realistic example: A chemical processing plant implemented just-in-time vendor access through a PAM platform. Vendor sessions were limited to specific assets, time-bounded to approved maintenance windows, and fully recorded. The first audit revealed three instances of vendors attempting to access assets outside their approved scope.

OT-safe verification: Audit access logs quarterly against your approved access matrix. Any access outside the defined scope is a finding requiring investigation.

Way 5 – Harden and Monitor Remote Access Paths

What it means in a factory context: Remote access to OT environments, for vendor maintenance, engineering support, and remote operations, is one of the highest-risk pathways in any factory network. Zero Trust treats every remote access session as untrusted until verified and continuously monitored.

Why it matters: The majority of significant OT security incidents in recent years have involved compromised or misused remote access pathways. Unmonitored VPN connections, standing vendor credentials, and direct remote desktop access to engineering workstations are consistently the paths of least resistance.

Implementation guidance:

• Eliminate direct VPN access to OT network segments, all remote access should terminate at a hardened jump host in an OT DMZ
• Require multi-factor authentication (MFA) for all remote access sessions, human and vendor alike
• Record all remote sessions, video capture of vendor sessions is increasingly standard practice
• Implement network access control that validates device posture before allowing remote connection, is the connecting device patched? Does it have endpoint protection?
• Deploy anomaly detection on remote access traffic, alert on sessions outside approved hours, unusual data volumes, or access to unexpected assets

Realistic example: A paper mill discovered through session recording review that a maintenance vendor was accessing historian data during remote sessions that had been approved only for PLC configuration work. The access was undocumented and outside the vendor’s contractual scope.

Operational benefit: Monitored, time-limited remote access reduces both security risk and vendor management complexity, every session is auditable.

Way 6 – Validate Device Trust and Firmware Integrity

What it means in a factory context: Device trust validation means verifying that OT assets on your network are what they claim to be and are running authorized, unmodified firmware, not a compromised or counterfeit version.

Why it matters: Firmware is the lowest software layer in any OT device and is therefore the hardest to detect if compromised. A PLC running modified firmware may execute commands differently than designed, with no visible indication at the HMI or SCADA level.

Implementation guidance:

• Establish a firmware baseline for all Tier 1 and Tier 2 OT assets, document the expected firmware version and hash for each device class
• Deploy firmware integrity monitoring through your OT security platform, alert on any device reporting a firmware version outside the approved baseline
• Enable secure boot on devices that support it, this hardware-level control prevents unauthorized firmware from loading
• Subscribe to vendor security advisories for all OT device models in your fleet and track firmware vulnerability exposure

Important safety note: Firmware updates require vendor-approved procedures, lab validation, and maintenance windows. Never apply firmware updates during production without engineering sign-off and a tested rollback plan.

Realistic example: An energy company’s firmware integrity monitoring platform alerted on a substation IED reporting an unexpected firmware version. Investigation revealed a firmware downgrade had occurred during a vendor maintenance session, restoring the approved version closed an exposure that had been present for six weeks.

Way 7 – Centralize Logging and Continuous Monitoring

What it means in a factory context: Centralized logging means collecting event data from all OT assets, network devices, and access systems into a single platform where it can be correlated, analyzed, and actioned in near real time.

Why it matters: Without centralized visibility, detection of a compromise depends on someone noticing something unusual in isolation, a standard that almost never catches sophisticated or slow-moving threats. Centralized monitoring enables correlation: a single event in isolation is noise; the same event combined with three others across different systems is a finding.

Implementation guidance:

• Deploy an OT-aware security monitoring platform that parses industrial protocols, standard SIEM tools cannot interpret Modbus or DNP3 traffic
• Establish communication baselines for all monitored segments, alert on deviations from normal communication patterns
• Define detection use cases specific to your factory environment: new device appearing on the network, unexpected cross-zone traffic, out-of-hours access, configuration change events
• Integrate OT monitoring alerts into your SOC workflow, with defined escalation paths for OT-specific events

Realistic example: A pharmaceutical manufacturer’s OT monitoring platform detected a Level 2 HMI attempting communication with an external IP address, a behavior inconsistent with its operational baseline. Investigation revealed a compromised HMI that had been used as a staging point for data exfiltration. The detection occurred within 4 hours of initial compromise.

What success looks like: Mean time to detect (MTTD) for OT incidents below 8 hours for Tier 1 assets; 100% of critical zone boundary traffic monitored.

Way 8 – Treat Backup, Recovery, and Incident Response as Part of Zero Trust

What it means in a factory context: Zero Trust extends beyond prevention and detection to include the assumption that a breach will eventually occur, and that the organization must be prepared to contain, recover, and resume operations with minimal downtime.

Why it matters: Ransomware incidents that encrypt OT systems demonstrate that recovery capability is a security control, not an afterthought. An organization that can restore a PLC configuration from an immutable backup within hours is fundamentally more resilient than one that faces a weeks-long recovery.

Implementation guidance:

• Maintain immutable, offline-tested backups of all OT device configurations, PLC programs, HMI configurations, historian data, and network device configurations
• Store backups in a physically separate location or an air-gapped repository, backups on the same network as the compromised systems are compromised too
• Test restoration procedures quarterly, a backup that has never been tested is a hypothesis, not a control
• Develop OT-specific incident response playbooks that define isolation procedures, notification chains, and recovery sequences for the top five incident scenarios

Realistic example: A discrete manufacturer recovered from a ransomware incident that encrypted engineering workstations within 14 hours, significantly faster than the industry average, because they maintained current, tested backups of all PLC configurations and could restore without vendor support.

Conclusion

Zero Trust is not a product you buy or a project you complete. It is a security posture, a sustained operational commitment to verifying every access request, limiting every privilege, and monitoring every session regardless of where it originates. For factories operating in an environment where connectivity and operational complexity only increase over time, it is the most defensible architecture available.

The 8 Practical Ways to Implement Zero Trust in Factories in this article are not a theoretical framework. They are a sequenced, operationally realistic starting point for organizations at any maturity level. Start with asset visibility. Layer in segmentation and access control. Build monitoring and recovery capability over time.

Zero Trust does not promise a breach-proof factory. It promises a factory that is harder to compromise, faster to detect, and more resilient when incidents occur. In industrial cybersecurity, that is the realistic and achievable goal.

Ready to assess your factory’s Zero Trust readiness? Contact CyberSec Magazine to be connected with qualified OT security assessment resources: contact@cybersecmagazine.com | +91 9490056002