IEC 62443 meets Zero Trust: How Cyber Resilience is created in OT Systems

For a long time, industrial plants were sufficiently protected - not because of technical defenses, but because OT systems were simply operated in isolation. However, this sense of security has changed fundamentally with the increasing networking in the wake of the Industrial Internet of Things (IIoT). Why does IIoT mark a turning point in any OT security strategy? Before we look ahead, we need to understand how it all began.

For example, IIoT has fundamentally changed OT security.

Before OT (Operational Technology) systems were connected to the internet, they were like isolated islands: they were designed for high availability and stable operation. Cybersecurity was considered secondary. Companies largely relied on the fact that there was no external accessibility.

This picture changed fundamentally with the Industrial Internet of Things (IIoT): OT systems were networked. Suddenly they were communicating via VPN, web interface or remote access.

This created a new vulnerability: an attacker only needed to bring a single packet into the OT island to manipulate processes, change configurations or even cause physical damage. The 2017 NotPetya ransomware demonstrated this impressively: production lines were paralyzed and high costs were incurred worldwide.

As soon as OT systems are networked, security and safety aspects must be equally planned and implemented from the outset.

New CISA assessment: Unsafe OT leads to high downtime and follow-up costs

On May 6, 2025, CISA, FBI, EPA and DOE published the fact sheet "Primary Mitigations to Reduce Cyber Threats to Operational Technology". It warns of ongoing cyberattacks on OT and ICS environments.

The energy, transport and water sectors are particularly affected.

If you don't act now, you risk major outages and considerable financial damage.

CISA Fact Sheet: These 5 recommendations protect against OT risks

Why IEC 62443 and Zero Trust are indispensable.

Two frameworks that work together perfectly in an integrated safety concept: IEC 62443 creates the framework, Zero Trust takes care of continuous monitoring.

To understand how the two approaches interact, it is first worth taking a look at their foundations - from the structural order provided by IEC 62443 to the continuous control provided by Zero Trust.

What is IEC 62443? The industrial safety belt.

Industrial plants are among the most attractive targets - and at the same time among the most difficult environments when it comes to safety. The IEC 62443 standard creates the necessary structure to secure complex OT systems.

Zero Trust: The logical and continuous security model

Modern attacks have long bypassed traditional protection mechanisms from within systems - often unnoticed and via legitimate accounts. This is precisely where Zero Trust comes in and establishes a security logic that no longer gives attackers any freedom of movement.

Strong synergy effects: IEC 62443 and Zero Trust

The combination of IEC 62443 and Zero Trust creates a strong and clear security architecture:

1. zones and communication paths (IEC 62443) as a basis for micro-segmentation (Zero Trust)

- Division into zones (e.g. Production, Mes, Engineering) defines which devices and services belong together.

- Zero Trust then determines how and when data may be exchanged between these zones.

2. security levels (IEC 62443) as the basis for risk-based access decisions (Zero Trust)

- Each device is assigned a security level (SL 1-4) depending on its criticality.

- Zero Trust guidelines use this categorization to prescribe stricter MFA checks for SL-4 controllers, for example, while SL-1 sensors are checked less restrictively.

3. clear responsibilities (IEC 62443) and technical implementation (Zero Trust)

- IEC 62443 defines who covers which area of responsibility (e.g. operations manager, security manager, system integrator).

- Zero Trust ensures technical control (e.g. dynamic policy adjustment, monitoring).

- In combination, IEC 62443 and Zero Trust prevent security tasks from getting stuck in silos.

Practical example: How IEC 62443 and Zero Trust protect together

FabrikTech AG (name changed by the editors) is a medium-sized manufacturing company that produces mechanical parts and previously had an outdated OT infrastructure.

The OT network structure was flat, there was no segmentation, many devices used default passwords and remote access was via simple port forwarding.

An employee accidentally clicked on a phishing link. Within minutes, a SCADA controller was infected and production came to a standstill. The damage was in the mid six-figure range, and there was also a considerable loss of reputation.

The attack exposed the true weaknesses. This was the starting point for a targeted transformation process that brings IEC 62443 and Zero Trust together step by step and secures the infrastructure in the long term.

1st gap analysis (IEC 62443 part 2 x): First, the current system architecture was analyzed and all assets were inventoried. Each device was categorized according to security level.

2. zone definition and communication channels: Clear zones were set up: Production, Mes, Office, External Partners.

3. zero trust framework:

Identity gateway: Each OT device logs in centrally and is authenticated.

Micro-segmentation: Only the SCADA server is granted read and write access to certain PLCs.

Continuous monitoring: A system monitors behaviour in real time and detects anomalies immediately. Access is automatically blocked in the event of suspicions.

4. hybrid protection for the future:

Lateral movement excluded: even if a phishing attack succeeds, the attacker cannot move from the office zone to the production zone.


Minimal downtime: a production shutdown could last a few hours at most because emergency procedures and manual operating modes are in place.


Audit?No problem: the company received top marks in the compliance audit because all processes are documented and reporting tools automatically generate reports.

The hybrid approach of IEC 62443 and Zero Trust optimally combines organizational and technical measures. This significantly reduces downtimes and costs in the event of an emergency.

Where does OT security stand in the age of Industry 4.0 and AI?

The OT landscape is evolving rapidly:

• Edge computing and AI-supported analysis: systems monitor plants in real time and detect anomalies even before failures occur thanks to machine learning.
• Autonomous production systems and digital twins: virtual images of physical systems (digital twins) enable simulations and predictions of how changes will affect operations.
• Cloud-integrated OT/IT concepts: Hybrid cloud solutions combine on-premises OT with modern cloud analytics.

Companies that focus on these trends at an early stage win:

• • Greater resilience: AI detects and reacts to cyber threats and anomalies in real time.
  • Faster innovation cycles: pilot projects in test environments can be efficiently transferred to live operation.
  • Proven compliance: IEC 62443 and Zero Trust are increasingly seen as a prerequisite for customers, investors and regulators.

Strengthen your OT security with the hybrid solution from InfoGuard

The path from an isolated OT island to a networked, resilient infrastructure cannot be achieved with individual measures, but only with a clear, prioritized security strategy.

The 4 most important findings from the CISA Fact Sheet:

1. 1. Remove OT assets from the public internet.
   2. Rely on strong authentication and password management.
   3. Segment IT and OT consistently.
   4. Practice emergency scenarios and ensure manual operating modes.

The combination of IEC 62443 and Zero Trust creates a holistic security concept that makes your company fit for the future.

Please remember: even a single open port can be a security-relevant weak point.

InfoGuard supports you in implementing this approach pragmatically and effectively. 350 experts are at your side in the DACH region, from gap analysis and zone and communication modeling to technical micro-segmentation, identity security and the development of audit-proof processes. The result is an OT security architecture that withstands attacks and meets regulatory requirements at the same time.

Don't wait until an incident makes your vulnerabilities visible! Design your OT security proactively. Contact us and together we will develop a resilient, future-proof security strategy that successfully protects your industrial facilities.

Caption: Image generated with AI