1. Broken Access Control (BOLA/IDOR)
The OWASP definition: Restrictions on what authenticated users are allowed to do are not properly enforced.
The Fintech Reality: This is the most destructive flaw in fintech apps today. In our testing, it frequently manifests as:
- A user changing the
accountIdparameter in an API request to view another customer's complete transaction history. - A merchant changing a
storeIdto process a refund against a different merchant's ledger. - An attacker finding a hidden
/api/v1/admin/users/freezeendpoint and calling it, successfully freezing accounts because the endpoint checked if the user was logged in, but not if they were an admin.
2. Cryptographic Failures
The OWASP definition: Failures related to cryptography (or lack thereof) which often lead to sensitive data exposure.
The Fintech Reality: Beyond just forcing HTTPS, this category critically affects data-at-rest and integration integrity:
- Storing BVNs, NINs, and full PANs (Primary Account Numbers) in plaintext in the database, making a simple SQL injection instantly fatal.
- Handling webhooks from NIBSS or Paystack without properly validating the HMAC SHA-512 signatures, allowing attackers to spoof successful deposit events.
- Using weak encryption (e.g., base64 encoding instead of actual encryption) for URL parameters passed between microservices.
Are your API endpoints actually enforcing ownership checks?
Get a Quick Security Check3. Injection
The OWASP definition: User-supplied data is not validated, filtered, or sanitized by the application.
The Fintech Reality: While modern ORMs have largely solved traditional SQL injection, we now see injection happening at the business logic and API layer:
- NoSQL Injection: Manipulating MongoDB queries via raw JSON input to bypass login checks (e.g.,
{"email": {"$gt": ""}, "password": {"$gt": ""}}). - Parameter Pollution: Sending two
amountparameters in a transfer request to confuse the backend validation logic while the processing logic takes the smaller amount.
4. Insecure Design
The OWASP definition: Risks related to design flaws and architectural weaknesses.
The Fintech Reality: This represents flaws in the core business logic that cannot be fixed by a simple code patch. Examples:
- Allowing users to register with an email address, completely verify their account, and then change their email address without requiring re-verification.
- Designing a loan disbursement flow where the funds are transferred via an external API *before* the internal ledger records the liability.
5. Identification and Authentication Failures
The OWASP definition: When user identity, authentication, or session management is not handled correctly.
The Fintech Reality: Account Takeover (ATO) directly follows these failures.
- OTP endpoints that do not rate limit, allowing attackers to script brute-force attacks against 4-digit or 6-digit pins.
- JWTs (JSON Web Tokens) that never expire, or systems that do not maintain a server-side blocklist to handle manual logouts.
- Password reset links that do not expire immediately after their first use.
Logic Flaws Rule Fintech
While the OWASP Top 10 is an essential baseline, our most critical findings in Nigerian fintech apps are almost always bespoke business logic flaws. Scanners can find missing security headers. Only engineers looking at the application logically will find that transferring negative ₦50,000 to another user actually increases the sender's balance.
Related services and resources
This guide covers the theory — for hands-on validation, see our penetration testing and vulnerability assessment services. For a developer-actionable checklist, use our fintech security engineering checklist. If you're navigating regulatory requirements, see our CBN compliance guide.
Frequently asked questions
What is the most common OWASP vulnerability in Nigerian fintech apps?
Broken Access Control (BOLA/IDOR) is the most destructive flaw we find. It manifests as users being able to view other customers' transaction histories, merchants processing refunds against other merchants' ledgers, and unauthenticated access to admin endpoints. It's the #1 vulnerability category by both frequency and business impact.
Can automated scanners detect OWASP Top 10 vulnerabilities in fintech?
Scanners can detect some infrastructure-level issues (missing headers, outdated TLS, known CVEs), but they cannot find the business logic flaws that cause the most damage in fintech — like negative transfer amounts, race conditions in disbursement logic, or webhook signature bypasses. These require manual testing by engineers who understand payment flows.
How does the OWASP Top 10 apply differently to fintech vs regular web apps?
Each OWASP category manifests uniquely in fintech. 'Injection' isn't just SQL injection — it's NoSQL injection bypassing login checks and parameter pollution manipulating transfer amounts. 'Cryptographic Failures' isn't just missing HTTPS — it's plaintext BVN storage and unsigned NIBSS webhooks. The standard needs fintech-specific translation to be actionable.
Should Nigerian fintechs go beyond the OWASP Top 10?
Yes. The OWASP Top 10 is an essential baseline, but the most critical findings in Nigerian fintech apps are almost always bespoke business logic flaws — negative transfer amounts increasing balances, race conditions in disbursement endpoints, or recovery flow chains enabling account takeover. These don't fit neatly into any OWASP category.