Security Design Patterns: Building Defensible Systems

Part of the Cybersecurity Skills Guide — This article is one deep-dive in our complete guide series.

By HADESS Team | February 28, 2026 | Updated: February 28, 2026 | 5 min read

Security design patterns are architectural decisions that make systems harder to compromise and limit damage when compromise happens. They are not tools or products — they are principles that shape how you build and connect components. Getting them right at design time saves months of remediation later.

Defense in Depth

No single control stops every attack. Defense in depth layers multiple independent controls so that failure of one does not mean total compromise.

A web application example: WAF filters obvious attacks, input validation catches malformed data, parameterized queries prevent SQL injection, database permissions restrict what queries can access, and network segmentation limits lateral movement if the database server is compromised. Each layer works independently. Remove any one, and the others still provide protection.

The mistake is treating defense in depth as “more firewalls.” It means diverse controls at different architectural layers — network, application, data, identity, and monitoring.

Least Privilege

Every identity — user, service account, application, container — should have only the permissions required for its function. Nothing more.

In practice: database accounts for web applications get SELECT/INSERT/UPDATE on specific tables, not DBA privileges. Kubernetes pods run with read-only root filesystems and dropped capabilities. IAM roles use resource-specific policies, not :.

Least privilege requires ongoing maintenance. Permissions accumulate over time as roles change and features are added. Schedule quarterly access reviews. Use just-in-time (JIT) access for privileged operations — grant elevated permissions temporarily and automatically revoke them.

Separation of Duties

No single person or system should control an entire critical process. Code review prevents a single developer from pushing vulnerable code. Infrastructure changes require approval from someone other than the requester. Financial transactions above a threshold need multi-party authorization.

In technical systems, separation of duties means the CI/CD pipeline cannot modify its own configuration, the monitoring system cannot be disabled by the systems it monitors, and backup operators cannot delete backup repositories.

Fail-Safe Defaults

When a system fails, it should deny access rather than grant it. If your authorization service is unreachable, requests should be rejected, not allowed through. If a firewall crashes, it should drop all traffic, not pass it.

Default-deny applies to everything: network rules (block all, allow specific), file permissions (no access, grant as needed), API endpoints (authenticated by default, public by exception).

A common violation: error handling that catches exceptions and continues processing with default values. If your access control check throws an exception, the default should be “deny,” not “skip the check.”

Complete Mediation

Every access to every resource must be checked against authorization policy. Caching authorization decisions creates gaps — if a user’s permissions change, cached decisions remain valid until they expire.

In web applications, this means checking authorization on every request, not just at login. Server-side enforcement at every API endpoint, not just the frontend. Validate access to specific resources (object-level authorization), not just roles.

Economy of Mechanism

Simple systems are easier to verify, test, and secure. Complex authentication flows with multiple fallback mechanisms have more attack surface than straightforward implementations. Choose boring, well-understood technology over clever architectures.

When reviewing a design, ask: can this be simpler? Every unnecessary component, protocol, or integration is an additional attack surface.

Related Career Paths

Security design patterns are foundational for Security Architect and Security Engineer career paths. Architects define these patterns for organizations, and engineers implement them in production systems.

Next Steps

• Test your architecture and design knowledge with the skills assessment
• Explore related topics in the skills library
• Get guidance on architect-track career planning from the coaching tool

Related Guides in This Series

• Agile Security: Embedding Security in Sprints and Development Cycles — HADESS | 2026
• AI/ML Security: Adversarial Attacks, Model Poisoning, and Prompt Injection — HADESS | 2026
• Compliance Management: SOC 2, ISO 27001, PCI DSS, and HIPAA — HADESS | 2026

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