If You Don't Know What You Have, You Can't Defend It

Let me tell you a hard truth most folks don't like to admit: You can't protect what you don't even know exists.

Sounds obvious, right? But in operational environments, where legacy gear hums quietly behind walls, and decades-old control systems still do critical work, asset visibility is still the Achilles' heel of most OT cybersecurity programs.

I recently revisited CISA's guidance on OT asset inventory. It's solid. It's practical. But it also underlines something I've seen again and again in the field: asset inventory isn't just step one. It's the foundation. And if that foundation is weak? Everything you build on top of it, your detection, response, segmentation, compliance, starts to wobble.

So let's talk about why this matters now more than ever.

We've all walked into a facility where the plant manager says, "Yeah, we know what's out there," and then points to a spreadsheet last updated in 2019.

That spreadsheet? It's probably missing:

• A couple of PLCs installed after an emergency repair.
• A third-party vendor's remote access box no one removed.
• A dozen unmanaged devices quietly communicating over Modbus.

And that's just the obvious stuff.

CISA reports that up to 60% of OT operators lack a complete, real-time asset inventory. That's not just bad hygiene, that's a security gap you can drive a truck through. Attackers love that kind of fog. It's where they hide. It's how they move laterally. And it's how they maintain access long after you think the threat is gone.

Most legacy inventory practices were designed for static environments. But today's OT networks aren't static, they're dynamic, hybrid, and increasingly connected to IT systems, cloud apps, and even mobile interfaces.

If your inventory can't adapt to changes in real time, it's out of date the minute something gets patched, swapped, or added.

That's why CISA emphasizes continuous discovery, not just scanning once a quarter. It also stresses the importance of passive monitoring when active scanning could cause disruptions (we've all seen an NMAP scan bring down a PLC, right?).

Real inventory today means:

• Hardware + software identification.
• Firmware and OS tracking.
• Protocols, services, and traffic mapping.
• Location and ownership.
• Communication paths between assets.

That's a tall order. But it's what's required if you actually want to defend your environment.

Here's where I think the CISA guide really nails it: asset inventory isn't just about knowing what's plugged in. It's about understanding risk in context.

Let me explain.

Let's say you have two assets running legacy firmware. One is air-gapped. The other is exposed via a third-party connection to a remote operator. Same vulnerability, completely different risk profile.

Without an accurate inventory tied to risk metadata, location, criticality, exposure, function, you're making blind decisions. You might patch the wrong thing. You might delay responding to the real threat. Or worse, you might think you're safe because your compliance checklist looks clean.

A lot of folks want to move toward automated response, AI-assisted threat detection, or compliance-as-code. But none of that works if your tooling has no idea what's on the network or what role it plays.

You need asset context. And that starts with a living, real-time, contextual inventory.

Think of it like this: asset inventory is the map. Without it, you're flying blind. And the more connected your environment becomes, the faster that map needs to update.

CISA recommends a phased, realistic approach, and I agree. Don't try to boil the ocean. Start with:

• Baseline your known assets (from configs, procurement, and staff knowledge).
• Deploy passive monitoring for real-time visibility without disruptions.
• Enrich with context: what does the asset do? Where is it? Who owns it?
• Build workflows to keep the inventory updated as changes occur.
• Involve both OT and IT from the beginning, don't silo discovery.

And most importantly? Treat it like a security project, not just an operations one.

In every breach investigation I've been part of, there was always at least one "surprise" asset. Something that wasn't on the books. Something that gave the attacker a foothold or a bridge.

Asset inventory may not be flashy. It's not AI. It's not a shiny new dashboard. But it's foundational. And in OT environments, where risk is measured in downtime, safety, and sometimes lives, it's non-negotiable.

You can't protect what you can't see. And until you fix that, nothing else you build will be as secure as you think it is.

Fragmented OT security isn't just risky. It's dangerous. And it's avoidable. If you're still managing OT and IT separately, you're staying one step behind attackers.

PhishCloud Cyber Fusion Center Strategies bring visibility, speed, and unity to your defenses—turning your weakest link into your greatest strength.

Ready to bridge the gap? Request a strategy call today HERE.