An essential strategy for protecting OT/IT convergence in sectors such as energy, water and transport

Today, critical infrastructures face an increasingly sophisticated cyber threat landscape. Sectors such as energy, transport and water, which are essential to the functioning of society, rely heavily on operational technology (OT) systems which, as they become increasingly interconnected with IT networks, exponentially increase their attack surface. This interconnection, although necessary to improve efficiency and control, has introduced new risk vectors that traditional perimeter-based security cannot effectively contain.

It is in this context that the Zero Trust approach becomes a key strategy. This model is based on a simple but powerful premise: never trust, always verify. In other words, no user, device or application should be implicitly trusted, regardless of whether they are inside or outside the corporate network. Every access request must be authenticated, authorised and continuously monitored. Applied to industrial environments, this paradigm represents a quantum leap in the protection of critical systems against increasingly targeted attacks.

Furthermore, Zero Trust acts as an enabler within a broader roadmap towards industrial digital transformation. In an environment where the digitisation of physical assets, the adoption of industrial IoT and real-time analytics converge, an industrial Zero Trust strategy enables the construction of secure critical infrastructures by design, integrating OT cybersecurity as a structural part of the new operating model.

OT cybersecurity in legacy industrial environments: a real challenge

OT systems were traditionally designed to operate in isolation, prioritising availability over security. As a result, many industrial infrastructures continue to use older devices that lack modern cybersecurity capabilities. Programmable logic controllers (PLCs), SCADA systems, and industrial sensors operate with unencrypted protocols, without authentication, and with operating systems that cannot be easily patched.

This situation makes these environments ideal targets for attackers who can exploit known vulnerabilities or use stolen credentials to access sensitive systems. Cases such as the attack on Colonial Pipeline (2021), where ransomware disrupted fuel supplies in the US, or the Triton malware (2017), which attempted to manipulate security systems at a petrochemical plant, demonstrate that OT attacks can not only cause economic losses, but also affect the physical safety of people and the environment.

In addition, the increase in connected devices (industrial IoT) and the need for remote monitoring have removed the old physical barriers. Perimeter security is no longer sufficient. An architecture is needed that considers the possibility that an attacker is already inside the system and acting with elevated privileges.

Added to this is the rise of industrial digitalisation, driven by Industry 4.0 and the need to collect, analyse and act on large volumes of operational data in real time. This transformation introduces even more entry points and increases the complexity of OT/IT architectures, requiring a comprehensive review of cybersecurity strategy.

Industrial Zero Trust strategy: key pillars for secure critical infrastructures

Adopting Zero Trust in industrial environments involves a progressive but feasible transformation that can be initiated by the most critical systems. These are the main measures:

Industrial network segmentation

Dividing the OT network into zones or segments reduces the risk of a threat spreading laterally. This micro-segmentation allows specific access rules to be applied to each zone, so that only authorised devices and users can interact with specific resources.

A practical example: if a plant operator suffers an attack on their workstation, segmentation prevents the malware from reaching critical control systems such as SCADA or PLCs. This measure contains the incident and facilitates its management.

In addition, technologies such as industrial firewalls, SDN (software-defined networks) and OT-specific security gateways can be applied, allowing granular control without interfering with operations.

Multi-factor authentication for OT systems

Applying multi-factor authentication to any remote or critical access to OT systems significantly increases security. Even if an attacker manages t te credentials, they will need a second or third factor (token, biometrics, etc.) to gain access. This is one of the pillars of Zero Trust and reduces the effectiveness of attacks based on phishing or password theft.

In industrial sectors, where external providers perform remote maintenance, the use of MFA becomes even more important to prevent unauthorised access.

Access control and minimum privileges in OT environments

Zero Trust requires that each user, system, or process have only the permissions strictly necessary to perform their function. Role-based access control (RBAC) allows permissions to be assigned in a granular manner, preventing an operator from performing critical actions that are not their responsibility. It also facilitates the traceability of actions, which is key in security audits.

Adaptive access policies (ABAC) can also be applied, which evaluate the context of access (device, location, time) and allow permissions to be dynamically adjusted. This is especially useful in distributed industrial environments or those with high staff turnover.

Continuous monitoring in OT networks

Constant monitoring of OT network behaviour allows the detection of anomalous patterns that could indicate a compromise. Modern solutions use artificial intelligence to identify lateral movements, unusual access or atypical commands in industrial systems. This visibility allows action to be taken before the attack has a real impact.

In addition, intrusion detection systems specific to industrial environments (ICS/IDS) can be deployed, capable of interpreting OT protocols and generating contextual alerts in the event of operational deviations.

Operational resilience in secure critical infrastructures

One of the most tangible benefits of Zero Trust is improved operational resilience. By assuming that attacks can occur at any time and designing the network to limit their effects, organisations gain responsiveness and recovery capabilities.

This is vital in environments where stopping operations is costly or could affect the population. For example, a water distribution company that applies segmentation and monitoring could continue to operate in secure mode even if part of its network is compromised. Avoiding total disruption and being able to isolate the threat is a competitive and reputational advantage.

In addition, the Zero Trust model enables the implementation of more effective incident response plans, immutable backups of critical data, and rapid restoration capabilities. This dramatically reduces downtime and the costs associated with cyberattacks, such as ransoms, reputational damage, or penalties.

Operational resilience is also strengthened through simulation exercises and network teaming, which allow for real-world testing of incident containment and recovery capabilities. These types of practices, increasingly required by regulators, allow for the identification of non-obvious gaps and the strengthening of internal protocols.

Regulatory compliance and Zero Trust: alignment with OT regulations

The European and global regulatory framework is rapidly evolving towards advanced security models. The European Union’s NIS2 directive establishes mandatory cybersecurity requirements for operators of essential services, including:

• Risk assessment and mitigation.
• Implementation of technical controls (MFA, segmentation, etc.).
• Incident response and business continuity plans.
• Incident notification within strict deadlines (24/72 hours).

Zero Trust is aligned with these requirements, as it incorporates measures such as strong authentication, access control, segmentation, monitoring and response from the design stage. Adopting it not only improves security posture, but also facilitates regulatory compliance and passing audits.

Also noteworthy is the international standard IEC 62443, specific to industrial automation and control systems. This framework recommends division into security zones, granular access control, secure updates and monitoring. All these pillars coincide with the Zero Trust philosophy.

Internationally, regulations such as NERC CIP in North America and reference frameworks such as the NIST Cybersecurity Framework promote practices consistent with Zero Trust. Aligning with these standards allows organisations to compete in regulated markets, strengthen their reputation and optimise compliance costs.

Real-life cases of OT cyberattacks: why you cannot trust by default

The recent history of attacks on critical infrastructure shows that implicitly trusting the OT environment can be devastating:

• Colonial Pipeline (2021): access to a corporate network via a VPN without MFA led to the preventive shutdown of fuel pumping, with massive economic and social impacts.
• Triton (2017): malware that attempted to disable the industrial safety systems (SIS) of a petrochemical plant. It sought to cause physical damage without being detected.
• Oldsmar (2021): An attacker accessed a Florida city’s water treatment system and attempted to dangerously alter chemical levels. Only the presence of an operator prevented massive contamination.

There have also been incidents in railway environments, ports and airports where malicious actors attempted to interfere with critical signals or communications. These examples reinforce the need to protect every access point, segment environments and apply continuous authentication.

In all cases, a Zero Trust architecture would have made intrusion more difficult, limited the scope of the attack and enabled faster responses.

Comparison: traditional security vs. industrial Zero Trust strategy

Aspect	Traditional perimeter model	Zero Trust approach
Internal trust	Implicit once inside the network	None, all access must be validated
Segmentation	Limited or non-existent	Mandatory and granular
Authentication	One-time at login	Continuous, multi-factor and contextual
Visibility	Partial or reactive	Complete and in real time
Lateral movement	High risk	Limited by design
Incident preparedness	Variable	Assumed from the design stage

This table illustrates the qualitative leap that Zero Trust represents compared to the traditional approach. Where previously it was sufficient to block entry, now every movement within the environment is protected. This radically changes the risk model.

Time to act: OT cybersecurity with a strategic vision

The digital transformation of critical infrastructure cannot be separated from an appropriate cybersecurity strategy. The Zero Trust model is not a futuristic option: it is a current necessity. Threats evolve, systems become interconnected and risks multiply. Ignoring this reality is like leaving a door open where there should be several locks and sensors.

Adopting Zero Trust does not mean rebuilding the entire OT architecture from scratch. It can be done in stages, starting with the most critical systems, remote accesses and assets with the greatest vulnerabilities. The return on this investment comes in the form of greater operational protection, better incident response and a stronger position with regulators and customers.

In sectors such as energy, water, and transport, where the impact of a security breach can be massive, Zero Trust is synonymous with responsibility, maturity, and continuity.

Because trusting by default is no longer safe. And because protecting what is critical requires no longer assuming that everything inside is trustworthy. It is time to verify everything. Always.