Understanding OWASP Top 10 - A4: Insecure Design Explained

Where Can We Find It?

Insecure design occurs when security is not considered during the development phase, leading to flaws that cannot be patched easily. This issue is found in:

Web Applications (Poor authentication, weak session management)
APIs (Exposing sensitive data by design)
Mobile Apps (Hardcoded secrets, improper data storage)
Cloud & IoT Systems (Misconfigured access controls)

How It Works?

Unlike coding mistakes (like SQL Injection), Insecure Design is a flaw in the system’s logic, architecture, or business rules. Even with secure coding practices, a bad design can still expose an application to attacks.

💀 Example 1: Password Reset without Verification

A user enters their email to reset their password.
The system immediately changes the password and sends it via email.
If an attacker enters someone else's email, they get full access without knowing the original password!
Fix: Require multi-step verification (OTP, security questions) before resetting passwords.

💀 Example 2: Unlimited Failed Login Attempts (No Rate Limiting)

A login page allows unlimited attempts without blocking the user.
An attacker can brute-force passwords using automated tools.
Fix: Implement rate limiting & CAPTCHA after multiple failed attempts.

Common Types of Insecure Design & Examples

1️⃣ Missing Security Controls

No authorization checks before accessing sensitive data.
Example: A normal user accesses an admin panel by entering /admin in the URL.

2️⃣ Flawed Authentication & Session Management

Weak authentication policies (e.g., no 2FA, session tokens in URLs).
Example: A banking site doesn’t expire session cookies after logout, allowing attackers to reuse them.

3️⃣ Excessive Data Exposure

API responses include more data than necessary.

Example: An API response leaks internal user details:

  {
    "user": "john_doe",
    "email": "john@example.com",
    "password_hash": "ab1234xyz",
    "role": "admin"
  }

Fix: Only return necessary fields in API responses.

4️⃣ Business Logic Flaws

Attackers abuse workflows to bypass security.
Example: A shopping website allows users to apply the same discount coupon multiple times by modifying requests.

5️⃣ Client-Side Enforcement Only

Relying on JavaScript validation alone instead of enforcing rules on the backend.
Example: A user disables JavaScript and enters negative values in a payment form to get money credited instead of debited.

How to Mitigate Insecure Design?

✅ 1. Implement Secure Design Principles from the Start

Follow Threat Modeling to identify security risks early.
Conduct security reviews before development begins.

✅ 2. Enforce Strong Authentication & Authorization

Implement Multi-Factor Authentication (MFA).
Enforce least privilege access (users should only access what they need).

✅ 3. Secure API & Data Handling

Follow REST API security best practices.
Only return minimum required data in responses.

✅ 4. Prevent Business Logic Abuses

Check workflow abuse scenarios (e.g., reusing coupons, bypassing payments).
Implement backend validation for all user actions.

✅ 5. Implement Rate Limiting & Session Security

Lock accounts after too many failed login attempts.
Expire session tokens after logout or inactivity.

Real-World Case Study: Uber's Account Takeover Flaw (2017)

What Happened?

Uber had a password reset vulnerability due to insecure design.
The system sent a 6-digit OTP via SMS, but did not limit failed attempts.
Attackers brute-forced the OTP and hijacked Uber accounts, leading to fraudulent rides and stolen payment details.

How They Fixed It?

✅ Implemented rate limiting & account lockout for OTP failures.
✅ Enforced Multi-Factor Authentication (MFA).
✅ Added device fingerprinting to detect unusual login attempts.

Lesson: Security must be built into the design phase, not added later! 🚀