Pentest for Fintech: What to Watch Out For

Fintech companies are stuck in an awkward split: they need to build and iterate faster than a traditional bank, yet are often held to the same security requirements. A pentest for a fintech platform therefore differs from a pentest for an average web application in a few important ways, and anyone who doesn’t know that difference ends up buying a test that doesn’t match the real risk.

You’re not just testing the application — you’re testing the flow of money

At a webshop, a vulnerability is annoying. At a fintech platform, a vulnerability can directly lead to financial loss, fraud, or bypassing limits and controls. That changes the scope of a pentest: alongside the usual application security (authentication, session management, input validation), there needs to be explicit attention to business logic. Can you manipulate transactions by replaying requests or reordering them? Are there race conditions around balances or limits? Is there a way to bypass approval steps?

You rarely find this kind of vulnerability with automated scanners. It requires a tester who understands how the financial process is put together, and who thinks as much like a fraudster as like a hacker.

API security takes centre stage

Almost every fintech platform runs on APIs: to banks, to payment providers, to KYC and identity verification services, and often to its own mobile apps. Every integration is a potential entry point. A thorough API pentest focuses specifically on authorization between endpoints (can user A reach user B’s data?), rate limiting, and how sensitive data (national ID numbers, account numbers, transaction history) moves through the chain.

Compliance is the starting point, not the endpoint

Depending on the type of service, a fintech company faces a combination of regulations: NIS2 for digital resilience, PCI DSS as soon as card data is processed, and for institutions supervised by DNB or the AFM, possibly also DORA. A pentest that only “ticks the box” for one of these frameworks, without genuinely testing the underlying risk, creates a false sense of security. The reverse is also true: a well-executed pentest almost always automatically satisfies the technical requirements of several frameworks at once.

Development speed calls for a different rhythm

Many fintech teams release weekly or even daily. A pentest that happens once a year then constantly lags behind reality. In practice, a combination works best: a thorough, annual external pentest on the whole platform, supplemented with smaller, targeted assessments around major releases or new features such as a new payment flow or a new API integration.

An example: the “technically correct, functionally leaky” trap

A recurring scenario in our engagements: every individual API call is technically well secured, with correct authentication and validation per request. Yet it turns out to be possible to have a transfer processed twice, simply by resending the confirmation request just before the first transaction completes — a classic race condition. No single line of code is “wrong”, but the combination of timing and missing idempotency creates a real financial risk. This kind of finding almost only surfaces with testers who deliberately hunt for business logic flaws, not with a standard automated scan.

What MonkeysICT pays attention to on fintech engagements

With fintech clients, we always combine application security with a business logic review: we don’t just look at whether a function is technically leaky, but whether the financial process around it can be abused. That requires testers who know the difference between “a vulnerability” and “a way to siphon off money” — and in fintech, those two are rarely the same thing.