The Hidden Cybersecurity Debt in Manufacturing

Cybersecurity debt in manufacturing rarely starts with a bad decision. More often, it starts with a reasonable one made at 2 a.m. when a line is down, a vendor needs access, or a production change cannot wait for the next maintenance window. A firewall rule is opened. A legacy system stays in service for another year. A local account is created because the normal identity path will not work on an older machine. Production comes back, everyone moves on, and the exception quietly becomes part of the environment.

I have learned to think of those decisions much like financial debt. Taking on some debt can be necessary. The problem is losing track of it. Across manufacturing environments, sites mature at different speeds, equipment can remain in service for decades, and new enterprise and cloud dependencies continue to appear around systems that were never designed for that level of connectivity.

The result is not simply “legacy OT.” It is a collection of old decisions that nobody has revisited. When operational change moves faster than architecture, ownership, and governance, temporary trust becomes permanent trust. That is where cybersecurity debt begins to turn into operational risk.

How Cybersecurity Debt Builds Inside Manufacturing

One lesson from working with OT environments is that a global security standard can look very different when it reaches the plant floor. One site may have well-defined network zones, current operating systems, documented assets, and clear ownership. Another may rely on specialized equipment whose vendor supports only an older operating system and whose maintenance window comes a few times a year. Treating those two sites as if they have the same starting point usually creates frustration rather than risk reduction.

Exceptions are another source of debt. A vendor may need temporary remote access to troubleshoot a machine. Engineering may need a firewall rule for a commissioning activity. A service account may be required because an application cannot use the organization's standard identity model. None of these requests is automatically wrong. In manufacturing, saying “no exceptions” is easy on paper and often unrealistic in practice.

The problem is what happens six months later. Is the firewall rule still required? Does the vendor still support that equipment? Who owns the service account? Was the temporary access ever removed? I have found that these simple questions often reveal more than another vulnerability scan.

For an exception to remain manageable, somebody needs to own it. There should be a clear business reason, a limited scope, and a point at which the decision is reviewed again. If those four things are missing, the organization is not only accumulating technical debt. It is accumulating ownership debt. Eventually, teams know that a connection or account exists, but no one feels confident enough to remove it.

Why More Security Technology Does Not Automatically Reduce Risk

Asset discovery is a good example of the difference between visibility and risk reduction. Finding a previously unknown controller or engineering workstation is useful, but the discovery itself does not tell us what to do next. We still need to understand what the asset does, who supports it, what it communicates with, how important it is to production, and what the operational impact would be if it stopped working.

Vulnerability management has the same challenge. In a typical enterprise environment, a critical vulnerability may trigger a patching deadline. OT is rarely that simple. A patch may require vendor approval, engineering testing, a scheduled shutdown, or validation that it will not change the behavior of a production application. Sometimes the right immediate action is not patching at all. It may be restricting access, removing an unnecessary route, tightening segmentation, increasing monitoring, or using another compensating control until the system can be safely changed.

This is why I am cautious about using vulnerability severity as the only measure of OT risk. A high-severity issue on an isolated, low-impact system may deserve a different response from a moderate issue on a production-critical asset with broad connectivity and limited recovery options.

The principle is straightforward: technology can enforce a security decision, but it cannot make the decision for the organization. A firewall can block traffic, but someone must first understand which traffic is legitimate. A remote-access platform can restrict a session, but someone must decide who should have access, to what, and for how long. Tools become valuable when they support those decisions, not when deployment of the tool is treated as the finish line.

Where OT Cybersecurity Debt Becomes Business Risk

Segmentation is where this becomes very visible. It is tempting to begin with firewall rules and VLANs. In practice, I prefer to begin with the process. What must communicate for production to run? Which systems exchange recipes, schedules, quality data, maintenance information, or control signals? Which dependencies are essential, and which are simply there because they have always been there?

Once those relationships are understood, segmentation becomes much more than a network exercise. It becomes a way to limit how far a problem can travel without breaking the communication that production actually needs.

The same thinking applies to third-party access. Manufacturers depend on specialized vendors, and in many cases those vendors know a particular machine better than anyone inside the company. The goal should not be to pretend that dependency can disappear. The goal is to avoid turning a legitimate support relationship into permanent standing trust. Access should have a purpose, a defined destination, appropriate identity controls, visibility, and an end point.

The OT trust boundary is also getting wider. Production can depend on enterprise applications, identity services, cloud platforms, data pipelines, engineering tools, and remote support. Something that appears to be an “IT system” can still have a very real production consequence when it fails.

A question I keep coming back to is: Which systems and people do we trust today, why do we trust them, and does that trust still need to exist? Asking it regularly exposes stale access and unnecessary dependencies that an inventory alone will not explain.

How CISOs Should Start Paying Down OT Cybersecurity Debt

Trying to fix every OT weakness at once is neither realistic nor useful. A better approach is to create enough context to make good decisions and then reduce debt in a repeatable sequence: Discover, Understand, Prioritize, Reduce, and Govern.

Discover what is actually there: assets, communications, remote-access paths, identities, and known exceptions. Then understand the operational context around them. Who owns the asset? What does it support? What depends on it? How would production be affected if it became unavailable? What safeguards already exist?

Prioritization comes next. I would not rank OT work by vulnerability score alone. Exposure, exploitability, operational consequence, criticality, recovery difficulty, and existing compensating controls all matter. This is also where cybersecurity and engineering need to make decisions together. Security may understand the threat; operations understands what a change could do to production. Both perspectives are necessary.

Reduction can take many forms. Sometimes it is a patch. Sometimes it is closing an old firewall rule, limiting a vendor account, removing unused connectivity, improving segmentation, replacing an unsupported system, or adding a temporary compensating control. The right treatment is the one that meaningfully lowers risk without introducing a larger safety or availability problem.

Governance is what keeps the debt from immediately returning. Exceptions need owners and review dates. Remote access needs a lifecycle. Security needs to be involved early enough in architecture changes to influence the design rather than review it after everything has been built.

This cannot be owned by the CISO alone. OT cybersecurity crosses engineering, infrastructure, manufacturing operations, procurement, vendors, and business leadership. NIST SP 800-82 Rev. 3, NIST CSF 2.0, and ISA/IEC 62443 all provide useful structure, but the day-to-day discipline still has to exist inside the organization. The goal is not zero exceptions. The goal is to know which exceptions exist, why they exist, who owns them, and when they will be challenged again.

Conclusion

Manufacturing will continue to have old equipment, limited maintenance windows, specialized vendors, and situations where an exception is the safest practical choice. Strong OT cybersecurity does not require pretending those realities will disappear.

What matters is whether the organization can still explain its decisions. When nobody knows why an access path exists, who owns an account, or whether a connection is still needed, cybersecurity debt has become unmanaged risk.

Paying it down is not a one-time remediation project. It is the habit of making trust visible, giving decisions an owner, removing what is no longer needed, and revisiting what remains. I would rather see an OT program steadily reduce unnecessary trust and improve its ability to contain and recover from disruption than simply count how many security products it has deployed. That is a much better measure of resilience.

References and Further Reading

National Institute of Standards and Technology (NIST). (2023). Guide to Operational Technology (OT) Security, NIST SP 800-82 Rev. 3. https://csrc.nist.gov/pubs/sp/800/82/r3/final 

National Institute of Standards and Technology (NIST). (2024). Cybersecurity Framework (CSF) 2.0. https://www.nist.gov/cyberframework 

International Society of Automation (ISA). ISA/IEC 62443 Series of Standards. https://www.isa.org/standards-and-publications/isa-standards/isa-iec-62443-series-of-standards 

Cyber Security Tribe. (2026, July 28). “Why Segmentation Must Become a Resilience Strategy.” https://www.cybersecuritytribe.com/articles/why-segmentation-must-become-a-resilience-strategy