How to Perform a Risk Assessment on Your OT Environment

Operational Technology (OT) environments, such as those found in industrial control systems (ICS), energy grids, manufacturing floors, and transportation infrastructure, have become increasing targets for sophisticated cyber attacks. Unlike IT systems, where confidentiality is traditionally paramount, OT systems prioritize availability and safety. A failure here isn’t a lost document; it's a halted production line or an environmental disaster.

Effective defense starts with understanding what you’re defending and which threats matter. This is the essence of risk assessment. In this post, we’ll cover pragmatic, technical, and architectural best practices for OT risk assessment, with historical notes and a focus on actionable steps—not pie-in-the-sky theory.

Why Risk Assessment Matters for OT

The early days of industrial control relied on “security by obscurity.” Legacy field devices—PLCs, DCS, RTUs and HMIs—were physically isolated and used proprietary protocols. But network convergence and the push for Industry 4.0 (or whatever buzzword du jour) have torn down these walled gardens. Now PLCs talk TCP/IP over Ethernet, and remote connections are common.

With this convergence, threat models must evolve. The Stuxnet incident (2010) was a watershed moment illustrating the catastrophic potential when OT is targeted. Later attacks on the Ukrainian power grid and ransomware campaigns (e.g., Colonial Pipeline, 2021) hammered this point home.

Risk assessment is the process that helps you weigh real-world threats against the capabilities and exposures in your environment.

The Foundations: Key Concepts in OT Risk Assessment

• Asset Identification: Cataloging what you have—systems, network segments, field devices, software, and firmware versions.

• Vulnerability Analysis: Identifying exposures that could be exploited. Can be technical (outdated OS, default credentials), procedural (weak change management), or physical (unlocked cabinets).

• Threat Modeling: Understanding who might attack (malicious insiders, nation states, script kiddies) and their likely objectives.

• Impact Analysis: Determining the consequences—environmental, business disruption, safety, financial, regulatory—if an incident occurred.

• Risk Estimation: Synthesizing the above into a clear risk picture, often using a rating matrix or qualitative scale.

Historical Note: Evolving from IT to OT Risk Models

Traditional IT risk frameworks (such as ISO 27005, NIST 800-30) grew from the premise that risk = likelihood × impact. In practice, many OT environments lack reliable incident probability data and face “high impact, low frequency” threat scenarios, leading to more qualitative or scenario-based assessments (e.g., the NIST 800-82 guidance and IEC 62443 series).

Step 1: Asset Inventory & Network Mapping

The first step isn’t glamorous, but it’s foundational: if you don’t know what you have, you can’t protect it.

1. Enumerate All Devices: Document PLCs, RTUs, field sensors, actuators, HMIs, engineering workstations, and network devices (switches, routers, firewalls).

2. Understand Connectivity: Map out network topologies, including VLANs, serial-to-IP bridges, wireless links, and remote access paths. Legacy fieldbus protocols (Modbus, Profibus) now often run over Ethernet—with all attendant risks.

3. OS and Firmware Baseline: Track patch levels, OS versions, and firmware. Many OT exploits (e.g., Triton/Trisis targeting Triconex SIS controllers) have zero-days that linger due to infrequent updates.

Tip: Be wary of automated discovery tools. Aggressive scanning can disrupt legacy OT devices that weren’t designed for it.

Step 2: Identify Vulnerabilities

Unlike IT, where CVEs and vendor patches abound, OT systems are often not publicly documented, and patching may be rare due to uptime concerns.

• Manual Review: Walk through device configurations. Are default credentials in use? Are network settings locked down?

• Protocol Analysis: Examine cleartext protocols (DNP3, Modbus/TCP, ICCP) for exposure to man-in-the-middle or replay attacks. Some protocols lack even basic authentication.

• Vendor Research: Cross-reference devices with public advisories (see CISA’s ICS-CERT, VDE, JPCERT, or vendor bulletins).

• Supply Chain: Are system integrators and contractors following your security standards, or introducing unknown risks?

Many OT operators still run Windows XP SP3 or embedded operating systems long past official support; risk assessment should explicitly call these out.

Step 3: Threat Modeling — Who’s Targeting You?

Even the best defense can be overwhelmed by a determined adversary using insider access, zero-days, or physical attacks. Effective risk assessment means clarifying:

• External Threats: Nation-state operations (APT33, Sandworm), cybercriminal groups, hacktivists.

• Internal Threats: Disgruntled employees, careless contractors, “helpful” maintenance personnel.

Scenario: A bridge between the corporate IT network and an OT system (for analytics) could be abused if IT credentials are compromised, as in the ransomware-induced shutdown of the Colonial Pipeline.

Step 4: Impact Analysis — What’s at Stake?

• Operational Disruption: How long can production halt before downstream costs become critical?

• Safety Consequences: Could a compromised controller result in plant damage, chemical spill, environmental hazard, or injury?

• Compliance and Reputation: Think NERC CIP (power), FDA (pharma), or ITAR (defense). Noncompliance can mean severe penalties.

Mapping asset classes to potential impacts (e.g., safety instrumented systems vs. non-critical sensors) focuses remediation where it matters.

An Example: Mapping the Purdue Model

The Purdue Enterprise Reference Architecture (PERA, 1990s) conceptualizes ICS into layers (Level 0 — Physical, Level 5 — Enterprise). Each layer has distinct risks and controls. Network segmentation—rare in legacy plants—is essential for limiting lateral movement when (not if) a breach occurs.

Step 5: Risk Estimation and Prioritization

Aggregate findings using a risk matrix: plot likelihood against impact and flag top “red” zones. Be honest about uncertainties and don’t overstate your detection or response capabilities.

• Does the business require all systems to be online, or can you tolerate loss of a legacy SCADA node?

• Are controls merely procedural or technically enforced (firewalls, access lists, unidirectional gateways)?

• Do you have logging or visibility in these environments, or is detection a hope and a prayer?

Step 6: Recommendations and Remediation Planning

Risk assessment that sits on the shelf is worthless. Use your findings to:

• Prioritize patching and hardening of systems supporting highest impact processes.

• Implement network segmentation to reduce attack surface; use firewalls and DMZs between IT and OT (reference IEC 62443-3-3).

• Review and tighten remote access pathways (disable direct RDP/VNC into OT, enforce multi-factor authentication).

• Develop incident response runbooks tailored to production realities (can you “pull the plug” safely?).

OT/IT Collaboration: Lessons Learned the Hard Way

Too often, IT and OT teams speak past one another. IT wants to patch, scan, and monitor. OT fears any disruption to mission-critical uptime. Bridging this gap takes empathy and cross-training:

• Involve OT engineers in risk reviews—only they understand process-level dependencies and “unwritten rules.”

• Educate IT staff on the challenges of 20-year-old embedded systems and safety constraints.

• Build mixed-response teams; run tabletop exercises that include operators and engineers, not just IT staff.

Conclusion

OT environments are not a footnote in security—they underpin national infrastructure and industrial safety. Effective risk assessment does not demand perfection or all-seeing monitoring; it demands honesty, diligence, and cross-disciplinary collaboration. Start with the basics: know your assets, understand your risks, and have a clear-eyed plan to mitigate the most dangerous ones. Network diagrams, access reviews, and honest dialogue between OT and IT staff accomplish more than any magic box with blinking lights.

In the end, performing a risk assessment on your OT environment is not a one-time effort but a discipline. Like code review or safety drills, it should be a recurring practice: learn from every change, every failure, every near miss. The attacks won’t stop; only your vigilance matters.