Critical Infrastructure

Security for environments where availability comes first.

Operational technology needs security work that respects uptime, safety, legacy constraints, and vendor support. Severnis assesses and strengthens IT/OT boundaries, communications, and systems using methods scoped to operational requirements, then helps remediate and verify the results.

Discuss an OT environment IT/OT integration capability

The environment

Systems built for reliability, now connected.

Critical-infrastructure and industrial environments rarely look like enterprise IT. They depend on systems designed for long service life and continuous operation, often spread across distributed sites and increasingly connected to business networks, cloud services, and remote users.

Security work in these environments may involve:

  • Supervisory and SCADA systems
  • HMIs
  • Engineering workstations
  • Historians
  • PLCs and RTUs
  • Industrial network infrastructure
  • Remote and geographically distributed assets

Operating principles

How OT security work should be done.

In operational environments, how a change is made matters as much as what is changed. These principles govern how Severnis approaches OT work.

  1. Availability-conscious

    Security changes are evaluated for operational impact first. Where a control can’t be applied safely, compensating measures are identified instead.

  2. Passive before active, where practical

    Discovery and visibility start with passive traffic, flow, and configuration analysis. Active techniques are used deliberately and within agreed limits.

  3. Authorized rules of engagement

    Testing is scoped to operational requirements and approved rules of engagement, with passive or low-impact techniques favored where appropriate.

  4. Coordinated change, planned rollback

    Changes are coordinated with operations staff, controls engineers, and integrators, scheduled into maintenance windows, and paired with tested rollback paths.

  5. Right-sized for legacy systems

    Legacy and hard-to-patch systems are protected through segmentation, access control, and monitoring rather than forced upgrades.

  6. Verified and documented

    Remediation is retested, and architecture, rule sets, and procedures are documented so the environment remains supportable.

Focus areas

Securing the IT/OT boundary and what sits behind it.

  1. IT
    Enterprise networkBusiness systems, identity, email, and cloud services
  2. Controlled conduit
  3. DMZ
    IT/OT demilitarized zoneHistorian replicas, remote access brokers, patch and file transfer
  4. Controlled conduit
  5. OT
    Supervisory & operationsSCADA and supervisory servers, HMIs, engineering workstations, and historians
  6. OT
    Control & fieldPLCs, RTUs, controllers, and industrial networks, including remote and distributed sites
Simplified layered reference architecture. Each zone boundary is a point where traffic is filtered, monitored, and limited to operational need.

  • Architecture & boundary assessment

    Review of IT/OT architecture, trust boundaries, and communications paths, informed by zone and conduit concepts.

  • Segmentation & firewall/ACL validation

    Rule review and controlled validation that enforced traffic matches operational need.

  • Controlled remote access

    Brokered, MFA-protected, and logged access for staff and vendors in place of ad hoc connections.

  • Asset & network visibility

    Passive traffic, flow, and protocol analysis to characterize devices and communications.

  • Industrial protocol review

    Characterization and security review of industrial communications and the systems that depend on them.

  • OT-aware vulnerability management

    Analysis and prioritization that account for patch constraints, vendor support, and operational risk.

  • Monitoring & detection

    Logging and monitoring visibility for OT networks, connected to existing detection and response workflows.

  • Remediation & validation

    Hands-on remediation support and retesting to confirm that changes achieved their intended effect.

Scope

Cybersecurity work, alongside process engineering.

OT security assessment and process engineering are different disciplines. Severnis performs the first and works alongside the people responsible for the second.

Severnis performs

Cybersecurity assessment and testing

  • Security assessment of PLCs, RTUs, HMIs, engineering workstations, historians, and industrial network infrastructure, when specifically authorized
  • Industrial-protocol characterization and security review
  • Controlled network-security validation of segmentation, access paths, and remote access
  • Remediation support and retesting
Owned by your engineering team

Process and control engineering

Process design, process optimization, and changes to control logic remain with your controls engineers, system integrators, and vendors. Severnis coordinates with them so security improvements fit the process rather than alter it.

Reference frameworks

Grounded in OT-specific guidance.

Work may be informed by recognized cybersecurity and operational-technology security practices, including NIST Cybersecurity Framework 2.0, NIST SP 800-82 Rev. 3, CISA Cross-Sector Cybersecurity Performance Goals, and applicable ISA/IEC 62443 concepts.

  • NIST CSF 2.0
  • NIST SP 800-82 Rev. 3
  • CISA Cross-Sector CPGs
  • ISA/IEC 62443 concepts

Reference frameworks inform the approach. They do not indicate certification, formal conformance, or endorsement, and engagements are not compliance assessments unless explicitly scoped that way.

Planning work at the IT/OT boundary?

Start with a conversation about your environment, constraints, and objectives.

Email info@severnis.com