Module 8 · OT / ICS at the Network Layer

Manish Garg
Manish Garg Associate of (ISC)² · RingSafe
Apr 22, 2026
6 min read
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Last updated: April 29, 2026

Stuxnet, Industroyer, Triton, Oldsmar. Why PLCs reachable from IT is catastrophic and common.

The Industrial Control Systems in a power plant, water treatment facility, or manufacturing line were designed for isolated networks. They’re now on IP networks, often with paths to the internet. This module covers why OT/ICS remains catastrophically vulnerable at the network layer — and why the gap between IT and OT security still produces nation-scale incidents.

Why this happens

ICS equipment has 15-30 year lifecycles. A PLC commissioned in 2005 is still running in 2026. It has the network security of 2005: clear-text protocols, no authentication, vulnerability to any packet sent by anyone on its LAN. You cannot patch it — vendor stopped shipping firmware updates in 2015. You cannot easily replace it — replacement is a multi-million-dollar facility-wide project.

Meanwhile, the business wants visibility into OT: historians pulling data to corporate dashboards, predictive maintenance using cloud analytics, remote access for vendor support, integration with enterprise MES. Every one of these use cases creates a network path from IT to OT.

The result: ancient unpatched systems connected to networks that eventually touch the internet.

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