Back to writing
Glib Rulev
Glib Rulev

OWASP TOP 4 - Insecure Design

You can’t code your way out of a bad design. That’s the core of OWASP’s A04: Insecure Design — a vulnerability that doesn’t arise from bad coding, but from flawed architectural decisions and missing security strategies from the start.

What is Insecure Design?

It’s about the absence of security in the blueprint of your system. No amount of secure coding can fix a feature that was never designed to be safe.

Example:

Consider a loan approval system with no built-in limits for how many times a user can resubmit an application. If a malicious user automates submissions to exploit approval logic — that’s not a coding bug. That’s a design failure: the system was never architected with abuse cases in mind.

Insecure Design shows up when:

  • Features lack security requirements altogether
  • Business logic allows risky behavior (like skipping a payment step)
  • Authentication is an afterthought
  • Rate limits and boundaries are never defined
  • Threat modeling was skipped — or never even considered

This isn’t about fixing code. It’s about how you think about security when designing the software.

Best Practices to Avoid Insecure Design:

  1. Security by Design: Integrate security from the first whiteboard session — not as an afterthought. Start threat modeling during the planning phase.
  2. Define Misuse and Abuse Cases: Go beyond “happy paths.” Map out how real-world attackers could twist the logic of your app for their benefit.
  3. Embed Least Privilege in the Design: Don’t wait for implementation. Plan granular permissions, roles, and boundaries during architecture discussions.
  4. Design Controls Upfront: Rate limiting, data validation, session timeouts — these should be designed into your system, not bolted on later.
  5. Conduct Architecture Reviews Regularly: Technology evolves. So do threats. Make secure design a continuous, living process — not a checkbox.

🔐 Bottom line: Insecure Design isn’t about “bad code.” It’s about missing the opportunity to design for safety from the start.

Let’s build systems that are secure by default — not just by intention.