10/2/2025 • 4 min read

Insecure Design: OWASP Top 10 Explained

Estimated reading time: ~9 minutes

The Problem

You can write perfect code — and still get hacked. Why? Because the design itself is insecure.

This is the core of Insecure Design, a category in the OWASP Top 10 that focuses on security failures baked into the system's architecture from the beginning.

What It Is

Security failures baked into the system's architecture. These aren't implementation bugs — they're fundamental design flaws that make the system inherently vulnerable.

Key Characteristics

Systemic Issues: Problems that affect the entire application design
Not Implementation Bugs: These are architectural decisions, not coding errors
Hard to Fix: Often require significant redesign to address properly
Prevention Focus: Best addressed during the design phase

Examples

Problem: Application allows unlimited login attempts Impact: Enables brute-force attacks and credential stuffing Design Fix: Implement progressive delays and account lockouts

Related: This directly leads to Authentication Failures and should be addressed in the design phase.

Problem: Application only supports password-based authentication Impact: Vulnerable to credential stuffing and password attacks Design Fix: Build MFA support into the authentication architecture

3. Financial App with No Anti-Fraud Checks

Problem: Payment processing without fraud detection Impact: Enables fraudulent transactions Design Fix: Integrate fraud detection and transaction monitoring

Related: Without proper monitoring, this becomes a Security Logging and Monitoring Failures issue.

4. Insufficient Session Management

Problem: Sessions never expire or use weak tokens Impact: Session hijacking and unauthorized access Design Fix: Implement proper session lifecycle management

5. No Input Validation Architecture

Problem: Application lacks systematic input validation Impact: Multiple injection and XSS vulnerabilities Design Fix: Design validation framework from the start

Why It Matters

Design flaws aren't fixed with patches — they require re-architecting.

Expensive to Fix: Requires significant development effort
High Impact: Can affect entire application functionality
Root Cause: Many security issues stem from poor initial design
Compliance Issues: May violate security frameworks and standards

Real-World Impact

Equifax (2017): Design flaw in Apache Struts led to massive data breach
Capital One (2019): SSRF vulnerability due to insecure cloud architecture design
SolarWinds (2020): Supply chain attack enabled by insecure software design

How to Prevent It

1. Perform Threat Modeling Early

Identify potential threats during design phase
Use frameworks like STRIDE or PASTA
Document security assumptions and requirements

2. Define Security Requirements as Part of Specs


# Example security requirements
authentication:
  - Must support MFA
  - Must implement rate limiting
  - Must use secure session management

data_protection:
  - Must encrypt sensitive data at rest
  - Must use TLS 1.3+ for data in transit
  - Must implement proper access controls

3. Use Secure Defaults in Frameworks

Choose frameworks with security built-in
Enable security features by default
Follow framework security best practices

4. Implement Security by Design Principles

Defense in Depth: Multiple layers of security
Fail Secure: System fails to secure state
Least Privilege: Minimal necessary permissions
Separation of Concerns: Isolate security functions

5. Regular Security Architecture Reviews

Review design decisions for security implications
Validate against security requirements
Update threat models as system evolves

6. Security Training for Designers

Educate architects on security principles
Include security experts in design reviews
Use security checklists during design phase

Tools

OWASP Threat Dragon: Free threat modeling tool
Microsoft SDL: Security Development Lifecycle framework
Rafter Handbook: Security best practices guide
STRIDE: Threat modeling methodology
PASTA: Process for Attack Simulation and Threat Analysis

Conclusion

Security isn't just code quality — it's design quality. Insecure design creates systemic vulnerabilities that are expensive and difficult to fix later.

Next Steps:

Conduct threat modeling for your current architecture
Review security requirements in your design phase
Implement secure design patterns and principles
Include security considerations from day one of your design process