Secure Design Review

Created: 2025-12-04 15:45
#note

Secure design review is a systematic examination of system architecture and design to identify security flaws, ensure adherence to security best practices, and validate that Software Security Requirements are properly addressed. It's a critical checkpoint in the Secure SDLC design phase, occurring before significant development effort is invested.

Overview

Security vulnerabilities often originate from fundamental design decisions rather than implementation bugs. A secure design review catches these architectural flaws early, when they're still relatively inexpensive to fix. This proactive approach prevents security issues that would be difficult or impossible to remediate through code-level changes alone.

Objectives

Validate that Threat Modeling findings are addressed in the design
Ensure security requirements are incorporated into architecture
Identify design patterns that could introduce vulnerabilities
Verify defense-in-depth strategies are implemented
Confirm that security controls are correctly positioned
Assess attack surface and minimize exposure
Review trust boundaries and data flow security

What to Review

1. Architecture Components

System decomposition and module boundaries
Component interactions and dependencies
Trust boundaries and security zones
Data storage and processing locations
External integrations and APIs
Infrastructure design (cloud, on-premise, hybrid)

2. Authentication and Authorization

Identity management approach
Authentication mechanisms (passwords, MFA, SSO, OAuth)
Session management strategy
Authorization model (RBAC, ABAC, etc.)
Token handling and lifecycle
Privileged access management

3. Data Security

Data classification and sensitivity levels
Encryption at rest and in transit
Key management and storage
Data retention and deletion policies
PII and sensitive data handling
Cross-border data transfer considerations

4. Input Validation and Output Encoding

Input validation strategies
Sanitization approaches
Output encoding mechanisms
API contract validation
File upload handling
Query parameterization

5. Error Handling and Logging

Error message design (avoiding information disclosure)
Logging strategy and sensitive data in logs
Audit trail completeness
Log protection and integrity
Monitoring and alerting integration

6. Network Security

Network segmentation strategy
Firewall rules and security groups
TLS/SSL configuration
Certificate management
DDoS protection
API gateway and rate limiting

7. Third-Party Components

Dependency selection criteria
License compliance
Known vulnerabilities in dependencies
Update and patching strategy
Vendor security assessment for Supply Chain Security

Review Process

1. Preparation

Gather architecture diagrams and documentation
Review Threat Modeling outputs
Collect Software Security Requirements
Identify relevant security standards and frameworks
Assemble cross-functional review team

2. Review Session

Walk through system architecture
Examine each component and interface
Discuss security controls and their placement
Challenge assumptions about trust and security
Document findings and concerns
Identify gaps and weaknesses

3. Analysis

Prioritize findings by risk
Assess feasibility of remediation
Consider alternative designs
Evaluate trade-offs (security vs. performance, usability, cost)
Map findings to security requirements

4. Documentation

Create detailed finding reports
Document security design decisions and rationale
Update architecture diagrams with security annotations
Record accepted risks and compensating controls
Create action items for remediation

5. Follow-up

Track remediation of findings
Re-review significant design changes
Update Threat Modeling based on design changes
Ensure findings are addressed in implementation phase

Common Design Flaws

Authentication and Session Management

Weak password policies
Insecure session token generation
Missing session timeout
Inadequate MFA implementation
Session fixation vulnerabilities

Authorization

Missing access controls
Confused deputy problem
Insecure direct object references
Horizontal/vertical privilege escalation opportunities
Over-privileged service accounts

Data Exposure

Storing sensitive data in plaintext
Using weak encryption algorithms
Inadequate key management
Exposing sensitive data in URLs or logs
Missing data classification

Input Handling

Trusting client-side validation alone
SQL injection vulnerability paths
Command injection possibilities
XML/JSON injection vectors
Path traversal opportunities

Architecture

Missing defense in depth
Single points of failure
Inadequate network segmentation
Exposed administrative interfaces
Missing security boundaries

Security Design Patterns

Good Patterns to Encourage

Defense in Depth: Multiple layers of security controls
Least Privilege: Minimal necessary permissions
Fail Secure: Secure defaults when errors occur
Separation of Duties: No single user has complete control
Zero Trust: Never trust, always verify
Complete Mediation: Check every access attempt
Economy of Mechanism: Keep design simple and understandable

Anti-Patterns to Avoid

Security by Obscurity: Relying on secrecy of design
Hardcoded Secrets: Credentials or keys in code
Monolithic Trust: Large trust boundaries
Client-Side Security: Trusting client validation
Improper Error Handling: Revealing system internals
God Objects: Components with excessive privileges

Review Checklist

All Software Security Requirements mapped to design elements
Threat Modeling threats have mitigations in design
Attack Surface Evaluation completed and minimized
Authentication mechanism appropriate for sensitivity
Authorization model enforces least privilege
Sensitive data encrypted in transit and at rest
Input validation implemented at trust boundaries
Error handling prevents information disclosure
Logging captures security-relevant events
Network security controls properly positioned
Third-party components assessed for security
Security testing strategy defined for Penetration Testing
Incident response plan considered in design
Compliance requirements addressed

Integration with Development

Findings should:

Be tracked in the same system as other development tasks
Block progression if critical security flaws exist
Be validated during Static Code Analysis and code reviews
Be tested during Penetration Testing
Inform Security Monitoring and detection strategies

Benefits

Early Flaw Detection: Identifies architectural vulnerabilities before implementation
Cost Savings: Fixing design flaws early is exponentially cheaper
Shared Understanding: Creates security awareness across the team
Compliance: Documents security due diligence
Quality: Improves overall system robustness and reliability

Challenges

Resource Intensive: Requires time from multiple skilled team members
Expertise Required: Need security architects or specialists
Subjectivity: Different reviewers may identify different issues
Resistance: Developers may view as process overhead
Keeping Current: Design evolves, requiring periodic re-review