Most security failures are not caused by missing tools.
They are caused by poor design decisions made early and never revisited.
Annex A 8.27 exists to ensure organisations apply secure system architecture and engineering principles throughout the system life cycle, embedding security into how systems are designed, built, operated, and changed.
This control is about security by design, not security after the fact.

Annex A 8.27 of ISO 27001:2022 focuses on secure system architecture and engineering principles.
At a practical level, this means:
This is a new control in ISO 27001:2022, reflecting the reality that most security weaknesses originate in architecture, not configuration.
Modern information systems are:
As complexity increases, so does the likelihood that:
Annex A 8.27 ensures organisations deliberately design systems to be secure, rather than relying on perimeter controls or reactive fixes.
This control replaces ISO 27001:2013 Annex A 14.2.5 and significantly expands the scope and intent.
A pragmatic approach to Annex A 8.27 typically includes the following elements.
Organisations should define a set of secure engineering principles that guide system design and implementation.
These principles commonly include:
Principles provide consistency across teams, systems, and technologies.
Secure engineering principles should apply during:
Security applied only at one stage is fragile.
Annex A 8.27 expects organisations to consider how:
Work together as part of a coherent system architecture.
Controls should reinforce each other, not operate in isolation.
Organisations should review system designs to:
Design reviews should occur:
Fixing architectural flaws later is expensive and disruptive.
Secure system architecture should consider:
Weak session handling is a common attack vector.
Annex A 8.27 explicitly supports:
This applies to:
Unchecked input undermines even strong perimeter controls.
Secure engineering principles should address:
This includes:
Resilience is a security property, not just an availability concern.
Architectures should consider:
Segregation reduces the impact of both attack and error.
Annex A 8.27 introduces explicit consideration of zero trust concepts.
This includes:
Perimeter trust assumptions no longer hold in modern environments.
System hardening should be considered part of engineering design, not post-build activity.
This includes:
Hardened systems fail less often — and fail more safely.
Annex A 8.27 expects organisations to consider:
Security controls should operate as a system, not a checklist.
Secure system engineering principles apply equally to:
Organisations should ensure:
Outsourced systems still shape internal risk.
Threats, technology, and architecture change.
Organisations should periodically review:
Static principles become outdated principles.
Annex A 8.27 does not require:
It does require organisations to:
Most breaches exploit predictable architectural weaknesses.
Architecture failures scale. Fixing them late is painful.
Annex A 8.27 is about building systems that remain secure even when things go wrong.
When secure system architecture and engineering principles are applied effectively:
Security controls operate on systems.
Architecture determines whether those controls succeed.
Annex A 8.27 ensures organisations get the foundations right.
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