In the world of Industrial Automation and Control Systems (IACS), a cybersecurity assessment is not merely an IT exercise. It is a high-stakes operational intervention that directly impacts physical safety, environmental compliance, and production continuity. For plant managers, OT engineers, and CISOs, the primary directive is clear: you cannot test industrial networks with the same tools used for corporate IT without risking catastrophic failure.
The common misconception is that a vulnerability scan is a “neutral” observation of network health. In reality, sending active probes to legacy PLCs, RTUs, and DCS controllers can cause buffer overflows, watchdog resets, and unplanned shutdowns. Red Trident advocates for a Safety First approach, where the assessment methodology is designed to protect the process before it protects the data.
This article outlines why traditional scanning fails in OT environments and details the specific, evidence-driven steps we take during our walkdowns to ensure accurate visibility without operational disruption.
Why Active Scanning is a Non-Starter for Industrial Networks
The most critical divergence between IT and OT security lies in availability. In an IT environment, a server rebooting after a scan is an inconvenience. In a manufacturing plant, an unplanned restart of a boiler management system or a chemical injection pump is a safety event.
Legacy protocols such as Modbus TCP, DNP3, and CIP were designed for deterministic communication over wired serial lines, not for the stateful connection tracking of modern firewalls. These protocols lack authentication and encryption. When an active scanner sends a rapid burst of SYN packets or malformed query strings to a legacy controller, it does not just get blocked; it overwhelms the CPU.
We have observed that active vulnerability scanners often misinterpret the silence of a non-responsive PLC as “firewall protection.” In truth, the device may be in a locked state, requiring a physical restart. This creates a false sense of security while simultaneously degrading the reliability of the monitoring system.
The Red Trident Method: Passive Discovery and Controlled Testing
At Red Trident, our engagement findings drive a specific assessment philosophy. We do not guess; we measure using passive traffic analysis first. Our approach combines scoping, passive discovery, controlled testing, manual analysis, stakeholder coordination, and practical reporting.
Step 1: Safety-Conscious Scoping
Before any tool is deployed, we define the “Kill Chain” of the physical process. We identify which assets are safety-critical. This involves mapping the network segments that house Siemens S7-1200/1500 PLCs, Rockwell ControlLogix controllers, and Siemens PCS7 DCS systems. We explicitly exclude active testing on any asset tagged as Life Safety or Environmental Critical.
Step 2: Passive Network Tapping (SPAN/Port Mirroring)
Instead of injecting traffic, we listen. By deploying passive taps on critical network trunks, we capture the conversation between HMIs, SCADA servers, and field devices. This allows us to build an accurate asset inventory without alerting the legacy devices.
The reality of incomplete inventories: In our assessments we’ve run, recurring issues involving incomplete asset inventories are prevalent. We frequently find “shadow IT” in OT—unauthorized wireless sensors or legacy routers that were never documented during commissioning. Passive discovery reveals these hidden assets because they appear in the traffic flows even if they are not in the CMDB.
Step 3: Controlled, Low-Intensity Testing
Once the passive baseline is established, we move to controlled testing. This is not a “fire-and-forget” scan. It involves:
- Rate-Limited Probes: Sending packets at intervals of seconds or minutes rather than milliseconds.
- Protocol-Aware Payloads: Using tools like Red Trident’s custom scripts that understand the nuances of OPC UA and Modbus to avoid triggering watchdog timers.
- Safety Interlocks Verification: Confirming that physical safety interlocks are still functional independent of the network state.
Evidence from the Field: The Cost of Ignorance
Theoretical frameworks like IEC 62443 and NIST SP 800-82 provide the “what,” but our engagement findings provide the “how it actually breaks.” We have documented specific failure modes that occur when operators ignore safety-conscious assessment.
Case Study: The Chemical Sector Program Review
In a 2017 technical review record located for a large petrochemical producer, we identified severe separation-of-duties concerns. An ICS Security Analyst role was also performing network/firewall/system administration. This created a single point of failure where any misconfiguration during an assessment could bypass all security controls.
Furthermore, the review highlighted a lack of patching coverage for non-Windows and standalone assets. The operator assumed that because the device did not run Windows, it was immune to standard exploits. In reality, the embedded OS in the controller had known vulnerabilities in its TCP/IP stack. When we eventually performed a controlled test, we found that the firmware was years out of date, exposing the plant to remote code execution risks via Modbus port 502.
This engagement record serves as a critical reminder: OT security is not just about the OS; it is about the protocol stack and the physical process.
The Internal Assessment Pattern
An internal assessment record from one of our recent road-show engagements noted that “every assessment” had recurring issues involving:
- Incomplete asset inventories.
- Missing or non-OT-specific security policies.
- Undefined security roles/responsibilities.
- Lack of adopted security standards/frameworks.
- Insufficient OT-specific awareness/training.
- Continuous monitoring not tied to business/security objectives.
Note that this internal statement is useful as a lead for finding the underlying assessment records; it gives no denominator or source set. However, it aligns with our broader findings where we consistently see a gap between IT policy and OT reality.
Bridging the Gap: From Visibility to Risk Reduction
Recent reports from Forescout Vedere Labs highlight that healthcare and water utility organizations lack adequate network segmentation and monitoring for OT systems. The Minnesota water utility attacks revealed major OT security gaps, emphasizing that legacy OT equipment remains unpatched and exposed to cyber threats.
The missing layer in these environments is not technology; it is the translation of visibility into risk reduction. Manufacturers are integrating OT security into ongoing operational processes rather than treating it as a post-assessment task. Organizations are prioritizing risk-based remediation strategies aligned with production goals.
Practical Remediation Strategies
When our assessments identify gaps, we do not simply hand over a PDF report. We work with the plant manager and OT engineer to prioritize findings based on:
- Safety Impact: Does this vulnerability allow an attacker to manipulate a physical process?
- Exploitability: Is the vulnerable service exposed to the internet or a corporate VLAN?
- Mitigation Feasibility: Can we apply a vendor patch, or do we need a compensating control like an OT firewall?
For example, if a legacy Schneider Electric PLC cannot be patched, we recommend implementing strict allow-listing on the perimeter firewall. This reduces the attack surface without touching the fragile device.
Conclusion: Safety is the Foundation of Security
An OT security assessment must be a safety-conscious, evidence-driven process. It combines scoping, passive discovery, controlled testing, manual analysis, stakeholder coordination, and practical reporting. By prioritizing safety, we ensure that the assessment itself does not become a threat to the very operations it aims to protect.
Red Trident stands ready to help you navigate this complex landscape. We offer a free OT security assessment consultation to discuss how our Safety First approach can be tailored to your specific industrial environment.
