Auditing ISO 27001 Annex A 8.27 Secure System Architecture and Engineering Principles is the technical evaluation of security-by-design throughout the system development lifecycle. The Primary Implementation Requirement is the application of multi-layered defense and zero-trust engineering, providing the Business Benefit of a resilient infrastructure that automatically mitigates lateral movement.
ISO 27001 Annex A 8.27 Secure System Architecture and Engineering Principles Audit Checklist
This technical verification tool is designed for lead auditors to establish the security integrity of system design and engineering lifecycle. Use this checklist to validate compliance with ISO 27001 Annex A 8.27.
1. Secure Engineering Principles Policy Formalisation Verified
Verification Criteria: Formally documented and approved engineering principles exist, defining the security requirements for all information system layers (application, data, and infrastructure).
Required Evidence: Approved “Secure Engineering Guidelines” or “System Architecture Policy” with version control and management sign-off.
Pass/Fail Test: If the organisation cannot produce a formal document specifying the mandatory security principles for system engineering, mark as Non-Compliant.
2. Defence-in-Depth Architectural Alignment Confirmed
Verification Criteria: The system architecture incorporates multiple layers of security controls so that the failure of a single control does not result in a total compromise.
Required Evidence: High-level design (HLD) or architectural diagrams showing layered controls (e.g., WAF, Firewall, IDS, Encryption, IAM).
Pass/Fail Test: If the architecture relies solely on perimeter security (e.g., just a firewall) with no internal segmentation or host-level security, mark as Non-Compliant.
3. Principle of Least Privilege in System Components Validated
Verification Criteria: Engineering designs ensure that system components and service accounts only have the minimum permissions necessary to perform their functions.
Required Evidence: System-to-system access matrices or IAM policy exports for service accounts (e.g., AWS IAM, Azure RBAC).
Pass/Fail Test: If service accounts or system components are found with “Owner” or “Global Admin” permissions by default, mark as Non-Compliant.
4. Zero Trust Maturity in Architectural Design Confirmed
Verification Criteria: The architecture demonstrates move towards “never trust, always verify” principles, specifically regarding identity-based access rather than network-location access.
Required Evidence: Configuration of identity-aware proxies, conditional access policies, or micro-segmentation logs.
Pass/Fail Test: If internal systems trust any traffic originating from the local network without further authentication or authorisation, mark as Non-Compliant.
5. Secure Default Configuration Standards Verified
Verification Criteria: Engineering standards mandate that all systems are deployed in a pre-hardened state with insecure defaults disabled.
Required Evidence: Infrastructure-as-Code (IaC) templates (Terraform/CloudFormation) or “Gold Image” build specifications showing hardened settings.
Pass/Fail Test: If the build process for a new server or cloud instance leaves default passwords or unencrypted storage active, mark as Non-Compliant.
6. Secure Component Reuse and Library Vetting Validated
Verification Criteria: A formalised process is in place to vet and approve the reuse of system components, APIs, and third-party libraries before architectural integration.
Required Evidence: Software Composition Analysis (SCA) reports or an “Approved Component List” maintained by the architecture team.
Pass/Fail Test: If developers or engineers can integrate third-party libraries into production architecture without a security vulnerability scan, mark as Non-Compliant.
7. Fail-Secure Mechanism Implementation Confirmed
Verification Criteria: Systems are engineered to fail in a secure state (e.g., closed) rather than an insecure state (e.g., open) during a component failure.
Required Evidence: Technical specifications or test logs for load balancers, firewalls, and application logic error-handling configurations.
Pass/Fail Test: If a security component (like an authentication gateway) defaults to “Allow All” traffic when the backend service is unavailable, mark as Non-Compliant.
8. Scalability and Availability Redundancy Verified
Verification Criteria: Engineering principles require the design of redundant processing facilities to ensure availability targets are met during peak loads or hardware failure.
Required Evidence: Auto-scaling group configurations or multi-availability zone (Multi-AZ) deployment logs in cloud environments.
Pass/Fail Test: If a critical system is engineered with a single point of failure (SPOF) that cannot meet the business RTO, mark as Non-Compliant.
9. Cryptographic Engineering Standards Validated
Verification Criteria: The architecture specifies the use of modern, robust cryptographic algorithms and centralized key management for data at rest and in transit.
Required Evidence: Technical design documents citing specific encryption standards (e.g., AES-256, TLS 1.2+) and KMS configuration screenshots.
Pass/Fail Test: If the system architecture permits the use of deprecated protocols (e.g., SSL 3.0 or TLS 1.0) for sensitive data exchange, mark as Non-Compliant.
10. Periodic Architectural Security Reviews Recorded
Verification Criteria: Management performs regular reviews of the system architecture to identify technical debt or emerging threats that bypass existing engineering principles.
Required Evidence: Architectural Review Board (ARB) minutes or Threat Modelling workshop reports conducted within the last 12 months.
Pass/Fail Test: If the organisation has not conducted a formal threat model or architectural review for its core processing facilities in the last year, mark as Non-Compliant.
| Control Requirement | The ‘Checkbox Compliance’ Trap | The Reality Check |
|---|---|---|
| Engineering Principles | Tool checks for a “Development Policy” upload. | Verify Architectural Implementation. Does the code/infra actually follow the policy? Policy is intent; IaC is reality. |
| Defence-in-Depth | Platform identifies “Firewall is active.” | Examine the Internal Traffic. GRC tools miss the “Flat Network” issue where an attacker can move laterally with ease. |
| Secure Defaults | Tool assumes cloud provider defaults are secure. | Check Baseline Drift. Verify that “Gold Images” haven’t been modified manually in the console without updating the template. |
| Least Privilege | Tool checks if MFA is on for the user. | Verify System Identities. GRC tools often ignore overly permissive service-to-service IAM roles in the cloud. |
| Component Vetting | Platform records “Snyk/SCA tool is integrated.” | Audit the Bypass List. Lazy engineers often “ignore” high-severity alerts in SCA tools to meet deadlines. |
| Fail-Secure | Tool records “Availability is high.” | Test the Failure State. Does the system lock down or open up when the IAM provider is down? GRC tools don’t test fail-states. |
| Redundancy | Tool checks if “Backup exists.” | Verify Regional Diversity. A GRC “tick” for backups doesn’t help if both the system and the backup are in the same AWS region. |
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