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Start by deciding whether remote access is necessary
List every way people or systems connect to operational technology (OT), including employee and vendor support, integrators, operators, peer systems, remote-support tools, and links between operational assets. CISA’s industrial-control-system guidance addresses these kinds of relationships and emphasizes managing remote access as part of the OT environment: Configuring and Managing Remote Access for Industrial Control Systems.
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For each connection, record its business or operational purpose, owner, user or role, target asset, approved method, and permitted scope of work. If the task does not require remote connectivity, remove the path. For access that remains, set a review date and disable accounts that are no longer needed; CISA specifically recommends least privilege and disabling dormant accounts in its May 6, 2025 OT mitigation fact sheet.
Keep OT assets off the public internet
When remote access is essential, CISA recommends a private IP network connection to remove OT assets from the public internet, alongside VPN functionality secured with a strong password and phishing-resistant MFA for user access. This is not a recommendation to publish an OT device, controller, or management interface at a public address and rely on a login to protect it.
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A VPN can protect a connection across an untrusted network, but it does not by itself determine which OT assets a person may reach, separate IT from OT, or ensure that access ends when the work is complete. CISA’s separate guidance on modern network-access security discusses vulnerabilities and misconfiguration risks in traditional remote access, and points to Zero Trust, Secure Service Edge (SSE), and Secure Access Service Edge (SASE) as approaches that can provide greater visibility. These approaches do not automatically replace OT-specific engineering and segmentation controls: CISA and Partners Release Guidance for Modern Approaches to Network Access Security.
Separate IT and OT, and narrow the permitted path
Maintain segmentation between IT and OT networks, as CISA recommends, and define only the traffic that must cross the boundary. Do not treat a successful VPN connection as permission to move freely through the environment. Scope authorization to the individual user or role, the relevant asset, and the agreed work. The fact sheet does not prescribe a universal network topology or firewall rule set; those depend on the site’s equipment, architecture, and operational needs.
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When evaluating a remote-access design, check whether OT remains unreachable from the public internet, how narrowly access can be assigned, whether authentication is phishing-resistant, whether sessions can be observed and ended, and whether the design preserves IT/OT separation. A design that improves user convenience but broadens network reach or weakens operational boundaries is not a secure trade-off.
Require strong authentication and prepare the endpoint
Require a strong password and phishing-resistant MFA for user remote access, consistent with CISA’s recommendation. The guidance does not specify a particular MFA product or protocol. A compatible hardware security key may be one way to provide phishing-resistant MFA, but confirm that it works with the organization’s identity platform and remote-access design; the key is only one part of the control set.
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Apply an endpoint-security baseline appropriate to the OT environment, and train employees, vendors, and other authorized users in the approved access procedure. CISA’s industrial remote-access practice discusses endpoint security and user education, but the appropriate baseline must account for the systems and support constraints at the site.
Make sessions visible and endable
Before enabling a method, establish how authorized staff can see that a remote session is active and how they can terminate it when requested or when the approved work is finished. CISA’s industrial practice states that “Session termination is a mandatory element of any secure remote access solution.” The document also discusses mechanisms for ending sessions on request or automatically. It does not establish a universal timeout value in the cited material, so set any timeout according to site policy and operational requirements rather than assuming one number suits every system.
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Define who can approve, observe, and end a session, and ensure the process works without creating an unsafe interruption to operations. The implementation should be assessed against safety, availability, vendor-support, and local policy requirements; international-partner guidance on OT cybersecurity likewise frames security decisions in the context of safe and secure operation: Principles of OT Cybersecurity for Critical Infrastructure Organizations.
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Use a repeatable approval and review workflow
- Inventory. Document each remote-access path, its users, purpose, owner, target assets, and connections to other networks or operational systems.
- Approve only necessary access. Remove unneeded paths and accounts. For each approved connection, document the user or role, asset, and scope of work.
- Select a protected route. For essential access, keep OT assets off the public internet and use private IP connectivity and appropriately secured VPN functionality, as recommended by CISA.
- Define boundaries. Maintain IT/OT segmentation and specify the traffic that needs to cross it. Confirm that the design does not grant broader reach than the task requires.
- Configure identity and endpoint controls. Require strong passwords and phishing-resistant MFA; prepare the user endpoint and communicate the approved procedure.
- Test session handling. Confirm that authorized staff can identify active access and terminate a session on request or through configured controls, while accounting for safe operation.
- Review and retire. Reassess access methods, permissions, dormant accounts, and exposure periodically and after relevant operational or security changes. Update the documented configuration when the approved design changes.
Fit controls to the OT environment
There is no single remote-access configuration established for every industrial site. A control that is suitable for one network, device, or vendor relationship may conflict with another system’s safety, availability, support, or operating requirements. Treat the guidance as a policy and architecture baseline, then validate implementation against the actual environment and local requirements. CISA’s ICS Recommended Practices index provides a broader set of industrial-control-system resources.
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