Many functional testers believe security is someone else’s responsibility—handled by penetration testers, security engineers, or external audits. But in reality, a large percentage of security vulnerabilities appear during normal functional testing flows: login, CRUD operations, role-based access, validation, and error handling.
The OWASP Top 10 isn’t just for security specialists. If you understand functional testing, you already touch most OWASP risks—you just may not label them as such.
This post explains the OWASP Top 10 from a functional tester’s perspective: what each risk means in simple terms, how it shows up during functional testing, and what red flags to watch for.
Why Functional Testers Should Care About OWASP
Functional testers validate whether a system behaves as expected. Security issues often occur when a system behaves correctly for the happy path but incorrectly for edge cases or misuse cases.
Examples:
- A user can view another user’s profile by changing an ID
- A logout button works, but the session remains valid
- A form accepts invalid input and crashes the backend
These are functional observations, but they map directly to OWASP risks.
Knowing OWASP helps functional testers:
- Raise higher-quality bugs
- Catch critical issues earlier
- Communicate more effectively with developers and security teams
- Contribute to “shift-left” security without new tools.
What Is OWASP Top 10?
OWASP (Open Worldwide Application Security Project) is a global community focused on improving software security. The OWASP Top 10 is a regularly updated list of the most critical web application security risks, based on real-world data.
It is widely used for:
- Secure development practices
- Compliance
- Risk assessments
- Security training
For functional testers, think of OWASP Top 10 as a lens to look at your existing test cases—not a separate testing discipline.
How Functional Testing Naturally Exposes Security Issues
Functional testing already covers areas where security problems hide:
- Authentication and authorization
- Input validation
- State transitions
- Business rules
- Error handling
- Data visibility
- A simple rule of thumb:If a feature can be tested functionally, it can often be abused functionally.
OWASP Top 10 Explained (Functional Tester View)
A01 – Broken Access Control
What it means: Users can access data or actions they shouldn’t.
How it appears in functional testing:
- Changing a URL parameter (/users/123 → /users/124)
- Accessing admin pages as a normal user
- Performing restricted actions via API even if the UI hides them
Some common bugs look like:
- UI blocks an action, but backend allows it
- Missing 403/401 responses
- Same API works for different roles
If a feature “works” for the wrong user, it’s a security bug.
A02 – Security Misconfiguration
What it means: Unsafe default settings or exposed internal features.
Functional tester clues:
- Debug endpoints accessible
- Stack traces shown on error pages
A03 – Software Supply Chain Failures
What it means: An application trusts external code, components, updates, or build pipelines that can be tampered with—and attackers exploit that trust.
Functional tester clues:
- App behavior changes without code changes
- Same version behaves differently across environments
- Builds failing or passing inconsistently
- Unexpected outbound network calls
- New permissions suddenly required
A04 – Cryptographic Failures
What it means: Sensitive data is exposed or weakly protected. In general, this happens because data in transit is not encrypted.
What functional testers may notice:
- Passwords or tokens visible in responses
- Sensitive data in URLs
- Application running on HTTP instead of HTTPS
- Tokens logged in console output or reports
A05 – Injection
What it means: User input is executed as commands or queries and is not treated as data.
Functional test signals:
- App crashes with special characters
- Database or stack trace errors in UI
- Unexpected behavior when entering invalid input
Examples during functional testing:
- ‘ OR 1=1 causing login issues
- Special characters breaking search
- File names causing errors
A06 – Insecure Design
What it means: The feature is risky by design, even if implemented correctly or another way of saying, a system is designed without caring about security.
Functional examples:
- Unlimited password reset attempts
- No rate limiting on critical APIs
- Business rule bypasses (e.g., skipping payment steps)
A07 – Authentication Failures
What it means: Problems with login, sessions, and identity management.
Functional test scenarios:
- Weak password rules
- Session still valid after logout
- Password reset without proper verification
- Multiple concurrent sessions not handled correctly
A08 – Software or Data Integrity Failures
What it means: The system trusts unverified data or updates.
Functional examples:
- File uploads without validation
- Importing data from untrusted sources
- Auto-updates affecting system behavior
A09 – Security Logging or Data Integrity Failures
What it means:
- Attacks happen, but nobody notices
- Data or logs are modified, injected, or trusted without verification.
What testers may see:
- No logs for failed logins
- No alerts for repeated errors
- Silent failures
- Log leaks sensitive data (token, password, …)
A10 – Mishandling of Exceptional Conditions
What it means: applications fail open instead of failing safe.
What testers may see:
- Duplicate orders, records … after clicking a button many times
- Show server error or bypass validation or data saved incorrectly
- Click Back / forward then UI shows failure or data is saved twice
- …
How Functional Testers Add OWASP Coverage (Without New Tools)
You don’t need penetration tools or scanners. Instead:
- Add negative scenarios
- Test with different roles
- Test back end validation
- Verify data is protected in transit, in log or database.
- No sensitive data is in URL
Conclusion: Functional Testers Are the First Security Gate
Functional testing is not security testing – but it supports security testing more than most teams realize.
By understanding OWASP Top 10:
- You improve test quality
- You catch critical issues earlier
- You become a stronger partner to developers and security teams
If a system works when it shouldn’t, it’s not just a functional bug – it’s a security risk.