OT Secure Remote Access

Why VPNs Alone Can No Longer Protect Industrial Environments

Remote access is no longer just a convenience for IT teams. In operational technology (OT) environments, the systems that run factories, utilities, and critical infrastructure, remote connectivity is a strategic risk decision. Vendors, engineers, and internal teams all require access to OT networks, but traditional VPNs create a broad attack surface rather than secure connectivity [1]. For OT, where downtime, safety, and physical consequences are at stake, this is not just an IT issue, it is an operational risk issue.

Why Traditional VPNs Are Risky in OT

VPNs were designed for IT environments. They assume that once a user is on the network, they can be trusted. In OT environments, that assumption can be catastrophic: a compromised vendor laptop may become a bridge into PLCs, HMIs, or historians; stolen credentials can allow lateral movement across production networks; and misconfigured VPNs can expose critical assets far beyond their intended scope. CISA guidance highlights that VPNs have been directly implicated in multiple high-impact compromises of critical infrastructure [2].

OT environments differ from IT in three critical ways. Many systems run for decades, making patching windows limited and downtime expensive. At the same time, the consequences of disruption are high: a single cyber incident can threaten safety, production, and regulatory compliance. Because of these differences, traditional network-based access models fail to provide the visibility, control, and resilience required in industrial environments.

Zero Trust: Moving Beyond the VPN

Zero Trust flips the old assumptions: never trust, always verify. Modern secure remote access solutions enforce continuous authentication, device posture validation, least-privilege just-in-time access, and session reauthorization. For OT, this means engineers can access a specific control system interface without exposing the entire control network. Zero Trust reduces the risk that compromised credentials lead to catastrophic lateral movement [1][2].

To reduce VPN risks further, modern architectures like Secure Service Edge (SSE) and Secure Access Service Edge (SASE) are recommended. SSE consolidates Zero Trust, Secure Web Gateway, CASB, and firewall services into a cloud-delivered model, simplifying policy enforcement and reducing reliance on exposed perimeter hardware. SASE integrates networking (like SD-WAN) with these security functions, providing consistent, centralized control and continuous visibility across multiple OT sites [1]. Together, these architectures allow organisations to enforce granular, risk-aware access while keeping control networks insulated from external threats.

Best Practices for OT Secure Remote Access

Based on CISA and international guidance, industrial organisations should adopt least-privilege access, strong identity controls such as MFA for all remote sessions, network segmentation by default, centralized monitoring and logging of all sessions, and continuous session validation that monitors user behaviour and device posture during the connection [1][2]. These measures provide both operational security and auditability, which are increasingly critical in OT environments.

NIS2 Considerations for EU-Based Operators

For organisations operating in the European Union, the NIS2 Directive introduces mandatory cybersecurity requirements that intersect closely with secure remote access strategy. Entities must implement strong access controls, including multi-factor authentication for all remote and privileged access, and ensure complete, auditable logs of remote sessions that can support compliance and forensic investigation [3][4]. Centralised logging and monitoring are not just operational tools, they are compliance obligations. Comprehensive, timestamped records of access activity, authentication events, and session details support both incident response and regulatory audits [4][5].

In practice, this means secure remote access solutions must provide detailed session logs tied to individual identities, evidence of MFA and access approvals, retention of security event data for audit and incident reporting, and support for regulatory reporting timelines, such as incident notification within 24–72 hours. This regulatory lens reinforces that modern Zero Trust and SSE/SASE architectures, which enforce granular access, strong identity controls, and centralized auditing, are not only better security practice but also a compliance imperative for organisations subject to NIS2.

Conclusion: Controlled Access Is the New Default

OT secure remote access is about controlled, observable, and auditable connectivity. Modern architectures built on Zero Trust, SSE/SASE, and robust identity management, combined with compliance awareness like NIS2, allow industrial organisations to reduce the risk of credential theft and lateral movement, maintain operational continuity and safety, and meet regulatory and audit requirements [1][5]. In short, secure remote access in OT is no longer optional, it is a strategic operational decision.

References

CISA & international partners, Modern Approaches to Network Access Security: www.cisa.gov/news-events/alerts/2024/06/18/cisa-and-partners-release-guidance-modern-approaches-network-access-security
CISA & partners, Guide to Securing Remote Access Software: www.cisa.gov/news-events/alerts/2023/06/06/cisa-and-partners-release-joint-guide-securing-remote-access-software
NIS2 Directive overview, access control and MFA requirements for remote access in the EU: www.wachendorff-prozesstechnik.de/en/product-groups/industrial-remote-maintenance/information-on/cyber-security/nis2/
NIS2 compliance and audit logging considerations, highlighting centralised session records: www.secomea.com/blog/compliance/nis2-how-secomea-helps-achieve-compliance/
NIS2 access control, MFA, and secure remote access guidance: www.isms.online/nis-2/implementing-guidance/access-control/mfa-scope/