Cross domain security: The backbone of national resilience

For many years, cross domain solutions – tools that enable the safe ,secure information transfer between networks or systems with different security classifications – have typically been seen as specialist tools for very specific environments. But that’s no longer accurate to the world we live in. Today, they’re one of the most important ways we can protect the UK’s Critical National Infrastructure (CNI).

When we talk about CNI, we’re not talking about abstract networks. We’re talking about the real-world, critical systems that keep the power on, ensure we get paid on time, keep hospitals and transport networks running, keep our water clean and move our goods around the country. They are the backbone of our society.

And, as has been widely publicised, CNI is becoming more connected and more interdependent every single year. That interconnectivity gives us huge opportunities, but it also brings a challenge: how do we allow information to flow freely enough to enable innovation, while keeping our most sensitive and safety critical systems protected from ever growing threats?

CNI in the crosshairs

CNI being a prime target for threat actors is nothing new. But, in the words of the UK’s National Cyber Security Centre (NCSC), “cyber incidents targeting organisations – particularly those against critical national infrastructure – are becoming more frequent, sophisticated and potentially destructive”.

It’s therefore no surprise that the government is taking steps to help drive resilience across the UK’s CNI ecosystem. In February, the NCSC issued an alert to CNI providers urging them to act now to protect against “severe” cyber threats, while the upcoming Cyber Security and Resilience Bill aims to enhance the UK’s cyber resilience and protect essential public services. You can read more about what the bill means for CNI operators here.

The challenge is that the threats we face today are not casual or opportunistic. They are patient, capable and in some cases state directed. And the consequences aren’t theoretical. They land in real services – from hospitals and water companies to food processing facilities – affecting real people.

This is the reality we have to design resilience for; a world where attackers don’t stop at the IT layer and where the systems that matter most are now within their reach. Today’s threat landscape highlights the importance of resilience by default – and cross domain security one of the places where that idea becomes real.

The power of cross domain

Cross domain isn’t just another box on a network diagram. It’s about making the flow of information safe, controlled and intentional between different trust zones, especially in environments where safety and reliability are so important. Cross domain supports this resilience in three powerful ways:

• 1 - It stops attackers moving freely across interconnected systems

In modern environments, the biggest risk often isn’t the initial breach; it’s what the attacker can reach afterwards. That’s especially true in Operational Technology (OT), where systems that were never designed for exposure are now being connected for good reasons. Cross domain solutions help contain compromise. They stop a single breach turning into something far wider. 

• 2 - It provides a guardrail against infected data

Whether it’s OT telemetry going to a cloud analytics platform or mission data moving between operational domains, one thing is always true: bad data creates bad decisions. Cross domain solutions validate, sanitise and check information before it crosses from one environment to another, reducing the risk of malformed payloads or hidden malware slipping through – thereby protecting the integrity of systems that cannot afford incorrect or manipulated data.

• 3 - It enables wider digital transformation

Every sector is modernising. OT is connecting to IT, analytics is moving to the cloud, automation is increasing, AI is entering operational environments – and none of that is slowing down. Cross domain capabilities let us do all of this without collapsing the boundaries that protect safety critical operations. They make secure digital transformation possible, not painful.

Bringing cross domain capabilities to bear

It’s for these reasons that the value of cross domain cannot be overstated. The positive news for the UK is that our approach to cross domain is grounded in consistent, nationally trusted NCSC principles that give us a shared way to design and assure cross domain solutions. They help make these capabilities repeatable, transparent and trusted, which is essential in high consequence sectors.

But technology alone isn’t enough. Cross domain solutions, and the resilience they bring, depend on strong governance, clear risk ownership, collaboration between government and industry and continuous assurance.

Organisations cannot operate in isolation. Threats don’t respect boundaries and neither should our approach to resilience. Cross domain gives us a way to work together – securely connecting environments, organisations, and missions without exposing what must remain protected. The threat landscape will not get simpler, but our response can be confident and strategic.

By investing in cross domain capabilities, we’re not just protecting networks. We are strengthening national security, safeguarding public trust, ensuring operational continuity and enabling innovation across the sectors that keep this country running. That makes it one of the most important tools we have in protecting the UK today and preparing for the challenges of tomorrow.