Many organisations contain systems that are interconnected in ways their designers never anticipated, and they rely on protocols that were not built to resist modern, sophisticated attacks. Attackers are increasingly able to uncover unknown vulnerabilities, and developments in AI will accelerate this further. Combined with supply chain changes that make it harder to gain deep assurance in products what are core to critical systems, cross domain is now an essential security approach for organisations operating across all sectors.
Our revised guidance is designed to ensure that cross domain is easier to implement so it can be more widely adopted across disparate sectors. It reflects how modern systems operate and how organisations now use technology to deliver essential services. At its core, cross domain is about safely enabling business functions, even when those functions span systems with different levels of trust. This could include importing documents, enabling video communications, or interacting with services hosted in other environments, such as over APIs.
Rather than focusing on fixed boundaries or specific technologies, the new approach looks at the end‑to‑end architecture needed to make these functions secure and reliable. A central part of this approach is developing an explicit understanding of:
- what data flows are required
- how systems are connected
- which threats are relevant, both individually and when systems are linked
Cross domain uses a sequence of functions—often referred to as a pipeline—to build confidence in data as it moves between trust zones. Each function prepares the data so the next stage can safely process it, or ensures that only valid data leaves a zone. This ensures assurance is gained across the entire flow, not at a single point.
