Risk
IEC 62443-Aligned OT Cyber Risk Assessments
A structured assessment of credible cyber threat scenarios, operational consequences, existing controls and risk treatments for a defined industrial control system.
When a risk assessment is needed
An OT cyber risk assessment supports a decision about a defined system or change. It is not a generic list of vulnerabilities. The assessment connects plausible events to process consequences, considers the controls already in place and records who must act on the remaining risk.
A broad OT cybersecurity assessment is more suitable when the immediate need is to establish an environmental baseline. A readiness review is the better starting point when the system boundary or available evidence is not yet clear.
Common triggers
- a new control system or supplier package will connect to an existing OT network
- remote access, data export or a corporate-system interface is being introduced or changed
- a project needs a defensible risk basis for zones, conduits or target security levels
- legacy equipment limits the controls that can be implemented
- risk ownership and the evidence needed for acceptance are unclear
System definition comes before risk scoring
Boundary and purpose
Define the control functions, assets, people and external services included in the system under consideration. Record exclusions and shared dependencies so risks are not assessed against an assumed boundary.
Zones, conduits and interfaces
Use the architecture to identify trust boundaries and required communication. A zone model informs the assessment; it should not be reverse-engineered merely to justify a preferred target security level.
Consequence and criteria
Agree how safety, production, environmental, financial and recovery consequences will be judged. The client retains responsibility for risk criteria and acceptance.
A target security level should follow the risk assessment. Selecting one from a generic checklist reverses the engineering logic and can create controls with no clear risk basis.
Assessment method
- 1.Define the system under consideration, operating purpose, boundaries, exclusions and external interfaces.
- 2.Agree risk criteria and consequence categories with people who understand safety, production, environment and recovery.
- 3.Develop credible threat scenarios from the architecture, access paths, dependencies and known weaknesses.
- 4.Assess existing controls from evidence, not from policy statements alone, and record uncertainty explicitly.
- 5.Evaluate risk and select treatments that are feasible within the operating and project constraints.
- 6.Assign actions and record residual risk for acceptance by the accountable client role.
Worked example: adding a monitoring connection
- Change
- A reporting server needs selected process data from an existing control network. The proposed design adds a firewall path and a server managed outside the control-system team.
- Credible scenario
- Compromise of the reporting environment is used to reach the control network through an over-broad rule or a shared administration path.
- Engineering review
- Confirm direction of initiation, endpoints, protocols, identity and management paths. Examine whether the transfer can be one-way or brokered and how failure affects operations.
- Decision record
- Document the selected architecture, rule constraints, hardening and monitoring actions, verification tests, responsible owners and the residual risk requiring approval.
This is a worked technical example, not a completed Meridian client engagement.
Outputs and boundaries
Assessment outputs
- system-under-consideration definition and interface summary
- assessment method, criteria, assumptions and limitations
- traceable threat-scenario and risk register
- existing-control and evidence record
- risk-treatment plan with owners, dependencies and verification needs
- residual-risk statement for the client's acceptance process
Not included unless separately scoped
- accepting or owning risk on the client's behalf
- process hazard analysis or quantitative safety assessment
- penetration testing or intrusive activity in a live control environment
- implementation of risk treatments or proof that every vulnerability has been found
If the assessment identifies architecture changes, the resulting actions can feed into network segmentation engineering. Requirements and test evidence can then be carried through design review, FAT and SAT assurance.
Related support and guidance
Related services
Choose this when your project needs specialist engineering capacity. A defined OT cybersecurity work package for risk, architecture, design review, supplier interfaces and assurance evidence within an active industrial project.
Discuss an OT cyber risk assessment
Share the system or project boundary, the decision the assessment must support and the evidence currently available. Sensitive technical material can be exchanged through an agreed channel after the initial discussion.