Why API security testing fails
Most companies believe their API is secure because they use HTTPS and require a login token. This is a catastrophic miscalculation. Encryption only protects the data while it travels over the network. A login token only proves who the user is. Neither of these controls verify if the user actually has permission to execute the action they requested.
Your frontend applications—your mobile apps, your dashboards, your web portals—do not enforce security. They only enforce user experience. If a developer hides the "Refund" button in the mobile app, the API endpoint for that refund still exists. Hackers do not use your mobile app. They talk directly to your API. If your API does not check permissions on every single request, your company will suffer a data breach. We perform manual fintech API security testing to find these exact flaws.
Do not wait for a data breach to find out your APIs are exposed. Book a manual security audit today.
Book an API Security TestWhat API security testing covers
We test every layer of your API - not just authentication, but the authorization decisions made on every single request. Automated scanners cannot do this. We map the business logic manually.
Object-level authorization
Can user A access user B's transactions, account details, or payment history by manipulating IDs? This is the most common and most dangerous API vulnerability in fintech products.
Function-level authorization
Can a regular user call admin endpoints? Can a merchant trigger refunds beyond their limit? We test every role against every endpoint.
Data exposure
APIs that return more data than the client needs - full account numbers, BVN fragments, internal IDs, or PII in error messages. We catalogue every instance of unnecessary exposure.
Rate limiting & abuse
OTP brute-force, credential stuffing, enumeration attacks. We verify that sensitive endpoints have effective rate limits that can't be bypassed with header manipulation or IP rotation.
Webhook & callback security
Payment confirmation webhooks that can be spoofed, callback URLs that accept unsigned payloads, and event handlers that don't validate source authenticity.
Integration boundaries
The handoffs between your backend and third-party services - payment processors, KYC providers, banking APIs. Where secrets are stored, how failures are handled, and what happens when the upstream lies.
API testing methodology
We map the documented and hidden API surface, then test each path through the product logic with valid and changed roles, objects, states, and amounts.
API surface mapping
We map every endpoint - documented and undocumented. We check for debug endpoints, legacy versions, and internal APIs exposed through client-side code.
Authorization matrix testing
Every endpoint tested against every role. We build a matrix of who should access what, then systematically verify that boundaries hold.
Business logic exploitation
We chain API calls in sequences that break business rules - transferring negative amounts, replaying idempotency keys, racing concurrent requests to bypass balance checks.
Advanced API attack vectors
Fintech APIs require a higher standard of testing. A standard web vulnerability might let an attacker steal a session cookie. An API vulnerability in a payment gateway lets an attacker steal a million dollars in five seconds.
Mass Assignment and Parameter Binding
Modern frameworks like Spring Boot, Laravel, and Django REST automatically bind incoming JSON payloads to backend database objects. If developers do not explicitly whitelist allowed fields, attackers can inject administrative parameters. We send massive JSON payloads to your update endpoints. We try to update fields like `is_admin`, `balance`, `tier_level`, and `kyc_verified`. If your API accepts those parameters, we escalate our privileges instantly.
GraphQL Introspection and Query Depth
If you run a GraphQL API, you face unique threats. We test if Introspection is enabled in production, which would hand us a complete map of every database schema and relationship you have. We test for query depth attacks, nesting requests hundreds of levels deep to exhaust your server memory. We test authorization at the resolver level, proving whether User A can pull User B's nested payment nodes.
Idempotency bypass in payment endpoints
Payment APIs must implement idempotency. If a mobile network drops exactly as a payment request is sent, the app might retry the request. If the backend processes both requests, the customer is charged twice. We use Burp Suite to duplicate requests identically. We strip the `Idempotency-Key` headers. We test how your transaction ledger handles race conditions and concurrent identical payloads.
Privilege escalation through stale tokens
Refresh tokens outlived logout. Admin actions checked permissions at login, not at execution. Expired sessions still carried full authority. Fix priority: this sprint.
Get a focused security test for your APIs, payment flows, and supporting applications.
Request a security reviewWhat your team receives
The report is engineering-focused. Every finding is tied to the specific endpoint, role, and product flow where it appears.
- Verified findings: Reproducible evidence tied to the affected endpoint, role, and product flow. We include the exact cURL commands required to reproduce the exploit.
- Authorization matrix: A clear record of which roles were tested against sensitive objects and functions. You see exactly what was tested and what held up.
- Engineering-ready fixes: Remediation guidance written for the implementation your team actually runs. We give you exact code snippets in your native framework (Spring, Django, Express).
- Management summary: Material risks, business impact, and priorities translated for executives and board members.
- Retest status: Confirmation when critical and high-priority fixes are ready for verification. You fix the bugs, we retest them, and we sign off on your compliance.
Related services and resources
API security testing frequently overlaps with payment gateway penetration testing, authentication and session security, mobile app testing, and web application testing. For implementation guidance, see the OWASP Top 10 for fintech and payment systems, our fintech API security testing steps, and the fintech API partner risk guide.
Frequently asked questions
What do we receive after an API security test?
You receive a technical report with verified findings, request and response evidence, affected roles and endpoints, business impact, remediation guidance, and retest status. We also provide a concise management summary and a walkthrough with your engineering team.
Do you test both REST and GraphQL APIs?
Yes. We test REST, GraphQL, gRPC, and WebSocket interfaces. Fintech products increasingly mix protocols - the gaps between them are often where authorization breaks down.
What about third-party API integrations?
We review how your application talks to payment processors, identity providers, and banking APIs. Specifically: how secrets are stored, how webhook payloads are validated, and what happens when upstream services return unexpected responses.
Can you test APIs that require authentication?
Yes. We test with authenticated sessions across multiple privilege levels - regular users, merchants, admins, and API key holders. Horizontal and vertical privilege escalation testing is standard.
How do you handle rate limiting testing?
Carefully. We test rate limit effectiveness on sensitive endpoints (login, OTP verification, password reset) without flooding your infrastructure. We validate that limits exist and can't be trivially bypassed.
Do you test APIs used by payment processors and payment gateways?
Yes. We test payment initiation, verification, refunds, settlements, webhooks, merchant isolation, idempotency, and administrative APIs. The engagement can cover the API by itself or the complete product, including its web or mobile clients.