APIs power the entire modern financial system. A mobile banking app is just a pretty interface. The real engine is the backend API. When a user sends money, the mobile app sends a request to your API. If that API is flawed, the money is gone.
Many Nigerian fintech startups focus all their security budget on their mobile apps. They obscure the mobile code. They add root detection. They implement complex biometric logins. This is a massive mistake. Hackers bypass the mobile app completely. They talk directly to your API using automated scripts. If your API trusts the client too much, they will empty your accounts.
At Simpa Labs, we specialize in fintech API security testing. We do not run generic network scans. We act like organized financial criminals. We map your entire transaction flow. We manipulate the data in transit. We find the business logic flaws that cost real money.
Why fintech APIs need special testing
Standard scanners find basic bugs. They find missing security headers. They find outdated software versions. But fintech APIs have complex business rules. A scanner cannot tell if a user changes a payment amount. A scanner cannot tell if a user spends money they do not actually have.
For example, a scanner sees a transfer endpoint. It checks for SQL injection. It finds nothing. The scanner marks the endpoint as secure. But the scanner does not realize that if you send the transfer request twice in the exact same millisecond, the system deducts the money once but credits the receiver twice. This is a race condition. Scanners are blind to race conditions.
We test how the money flows. We think like hackers who want to steal funds. We manually test your business logic. This is the only way to find the real flaws that scanners miss. We look at every single trust boundary. We assume every incoming request is hostile.
Continuous testing vs. Point-in-time
Many companies order one penetration test a year. That is point-in-time testing. It is not enough. You push new code every week. You build new features every day. If you introduce a massive vulnerability in February, an annual test in November will not save you. You will get breached in March.
We believe in continuous testing. We show you how to shift left. This means you test your code while you write it. We help you add security tools to your CI/CD pipeline. These tools scan every pull request. They catch the easy bugs. They stop developers from hardcoding API keys in the source code.
Once the pipeline catches the simple errors, our human experts come in. We hunt for the complex business logic flaws that the tools missed. This hybrid approach gives you the speed of automation and the deep insight of manual adversarial engineering.
What we look for in our tests
We hunt for the exact bugs that cause massive data breaches. We use the OWASP Top 10 for APIs as our map. We look for authorization failures. We look for data leaks. We look for rate limit bypasses. Here is what we test in every single engagement.
BOLA (Broken Object Level Authorization)
BOLA is the number one API killer in the world. It destroys companies. We check every single link that uses an ID. We see if User A can open User B's wallet. If your server does not check who owns the wallet, hackers can steal massive amounts of data in seconds.
Developers often check if a user is logged in. They forget to check if the user actually owns the data they are asking for. A hacker simply changes the account number in the URL. If the server hands over the data, the hacker writes a script to download every single account on the platform.
# We test if User A can view User B's data
curl -X GET https://api.fintech.com/v1/wallets/wlt_002 \
-H "Authorization: Bearer USER_A_TOKEN"
# If we get a 200 OK, you have a BOLA flaw.Business logic flaws and payment changes
We try to break your payment rules. We change the payment amount before we send it to the server. We try to pay negative amounts. We try to buy a $100 item for $1. If your backend trusts the frontend too much, we will find it. Scanners completely miss these logic gaps.
We test your webhook endpoints. When Paystack or Flutterwave tells your server a payment succeeded, we intercept that message. We copy it. We send it to your server fifty times. We check if your server credits the user fifty times for a single payment. We test idempotency. We ensure your system cannot be tricked by replay attacks.
Token security and broken authentication
We attack your JWT tokens. We test if they expire correctly. We try to change the role inside the token from "customer" to "admin". We check if your server actually signs the token with a strong secret key. We test if we can forge our own tokens.
We also try to steal session tokens. We use cross site scripting attacks on your admin dashboards. We check if your tokens are stored securely in the browser. We ensure you use HTTPOnly cookies. We check your mobile app storage. We rip the tokens out of your mobile app caches and replay them from a different continent to see if your API notices the IP address change.
Rate limiting bypass
Hackers use fast bots to guess OTP codes. We test your login and OTP endpoints. We send thousands of fake login attempts in one minute. We make sure your server blocks attackers who try to guess passcodes too fast. We ensure you lock out brute force attacks immediately.
We do not just stop at basic rate limiting. We test for advanced bypasses. We rotate our IP addresses. We append null bytes to the end of our email addresses. We use HTTP header manipulation to trick your web application firewall. If there is a way to brute force your customer accounts, we will find it before the criminals do.
Mass assignment and hidden fields
We try to edit hidden fields. We create a new user profile. We send the standard fields like name and email. But we also sneak in a secret field like "is_admin: true" or "kyc_level: 3". If your server accepts our secret field, we just gave ourselves admin rights without any hacking tools at all. We test every single form for mass assignment bugs.
This happens because modern frameworks map JSON input directly to database objects. It is very fast for developers. It is also very dangerous. We test exactly which fields your API accepts and which ones it updates. We map the entire data model from the outside.
Excessive data exposure
We check what data your server sends back. Sometimes an app only shows the user's name on the screen. But the server actually sends the user's name, home address, phone number, and password hash in the background code. We read the raw API traffic to catch excessive data exposure.
This flaw causes massive privacy breaches. The developer thinks the data is hidden because the mobile app does not display it. The hacker uses an intercepting proxy and reads the raw JSON response. The hacker sees everything. We find these leaks and tell you exactly which endpoint is spilling data.
BOLA exposed 50,000 customers
We tested a payment app. The history link used a simple ID. We changed the ID. The server gave us the full history of a stranger. We downloaded 50,000 records in ten minutes. The records contained names, transaction amounts, and bank account numbers. We reported it immediately. The engineering team fixed the authorization logic in one hour. We saved them from a company killing data breach.
The anatomy of a Simpa Labs report
We do not hand you a messy PDF full of scanner trash. We hate generic reports. We write clear, actionable reports for your engineering team. We respect your time. Here is what you get when you hire us:
- Executive Summary: A plain English overview for your CEO and board. We explain the exact financial risk of the bugs we found.
- CVSS Scoring: We rank every bug by risk so you know what to fix first. Critical bugs get fixed today. Low risk bugs go into the backlog.
- Reproduction Steps: We write out the exact terminal commands we used to break your app. Your engineers can copy and paste our code to see the bug happen live. There is no guessing.
- Remediation Advice: We give you the exact code snippet you need to fix the flaw forever. We show you the right way to write the authorization logic.
Compliance mapping: NDPA, CBN, and PCI DSS
You test your API to stop hackers. But you also test it to pass audits. We map every single bug we find to the major compliance laws. Your auditors will love our reports.
If we find a data leak, we tell you exactly how it violates the NDPA (Nigeria Data Protection Act). If we find a payment flaw, we map it directly to the PCI DSS rules. If we find an auth bug, we link it to the Central Bank of Nigeria cybersecurity guidelines.
Our Head of Compliance Oversight reviews every report before we send it. We ensure your final document satisfies the toughest enterprise partners and banking regulators in Nigeria. We make compliance easy.
API security is not a checkbox. It is the core defense of your entire business. If your API is weak, your business is weak. Do not trust automated scanners to protect your transaction engine. Hire adversarial engineers who know exactly how to break modern financial systems.
Secure your API before a hacker finds the weak spot. Pass your next audit.
Book an API Security TestMore frequently asked questions
What API systems do you test?
We test all REST APIs. We test Node.js, Python, Java, and Go. We also test GraphQL and webhooks. The language does not matter. The security logic matters.
Do you need our API documentation to test?
We prefer your OpenAPI or Swagger files. It saves time. But we can also test without them. We act like hackers and find hidden endpoints on our own.
How do you handle live production data?
We test on a staging server first. If we must test in production, we move slowly. We track every action to keep your data perfectly safe and avoid breaking real transactions.
What is the biggest risk in a fintech API?
BOLA (Broken Object Level Authorization) is the biggest risk. Hackers change an ID in the URL and steal another user's money or data. We hunt for BOLA in every single test.
Do you test for CI/CD pipeline vulnerabilities?
Yes. We show you how to shift left. We help you put basic security checks right into your code pipeline. This stops simple bugs before they ever reach the live server.
Related reading
Blog: BOLA in payment APIs · JWT token mistakes · Rate limiting APIs