Security for Fintechs: finding the IDOR before the attacker
Fintechs grow fast, with lean teams and public APIs that move real money. Decripte works on the three fronts that decide the game: finding the authorization flaw before the fraudster, responding to the incident with containment in under an hour, and building a continuous API security program.
Direct answer
To protect a fintech, start with the layer where money and data actually flow: the APIs. The most effective measure is validating object-level authorization (preventing BOLA/IDOR) on every endpoint that returns a balance, statement, transaction, or personal data, combining recurring API pentesting with 24x7 SOC monitoring to detect abuse in real time. In parallel, you must treat secrets and keys as high-risk assets (vault, rotation, no credentials in code), shrink the exposure window with continuous vulnerability management, and maintain an incident response plan with a containment SLA that stops the bleeding within one hour. Decripte delivers this set in an integrated way, aligned with the requirements of PCI-DSS, LGPD, and the Central Bank regulations applicable to payment institutions.
24/7
SOC monitoring APIs and transactions
<=1h
Containment SLA for incidents
PCI-DSS
Requirement for anyone processing cards
OWASP API Top 10
The basis of our API pentesting
In summary
- ›The biggest risk surface of a fintech is not the network, it's the API: authorization flaws (BOLA/IDOR) let one user see another's data without 'breaking' anything — the system simply hands it over.
- ›Recurring API pentesting finds the authorization flaw before the fraudster; the 24x7 SOC detects the abuse in real time when the flaw slips through.
- ›Leaked secrets and keys are the favorite shortcut for ransomware and fraud; a vault, rotation, and repository scanning close that door.
- ›Incident response with containment within 1h limits the financial, regulatory (ANPD/Bacen), and reputational damage before it escalates.
- ›Fintech security is a continuous program, not a one-off audit: with every deploy, a new endpoint is born that needs to be tested.
- ›Compliance (PCI-DSS, LGPD, ISO 27001) stops being a cost and becomes a commercial differentiator when structured early.
Cibersegurança para Fintechs
Fintechs grow fast, with lean teams and public APIs that move real money. Decripte works on the three fronts that decide the game: finding the authorization flaw before the fraudster, responding to the incident with containment in under an hour, and building a continuous API security program.
Why fintechs are a priority target — and why the API is the epicenter
Fintechs are born with a competitive advantage that is, at the same time, their greatest security weakness: speed. Small teams ship features in short cycles, expose public APIs for partners, apps, and Open Finance integrations, and scale their customer base long before the security function matures. The result is an attack surface that grows at an exponential pace while controls grow at a linear pace. Every new API route is a door; every third-party integration is a key handed to someone you don't control.
The aggravating factor is what lies on the other side of those doors. Unlike a blog or a low-ticket e-commerce site, a fintech moves real money and holds sensitive financial data in custody: balances, statements, document numbers, card data, transaction history. This turns the company into a target for two distinct adversary profiles. On one side, the fraudster, who seeks to abuse business logic and authorization flaws to extract value directly. On the other, the ransomware operator, who seeks access to encrypt, exfiltrate, and extort. Both converge on the same weak point: the API.
The API concentrates the risk because it concentrates the value
In modern fintech architectures, the web interface and the mobile app are merely clients. The intelligence, the state, and the money live behind the API. That's why, when we talk about security for fintechs, we're not primarily talking about network firewalls or endpoint antivirus — we're talking about how each request is authenticated, authorized, and validated before returning a balance or approving a transfer. It is precisely in this layer that the most dangerous and least visible flaws live.
What changes in a fintech
- ›The API is public by design — it needs to be accessible to apps and partners, so 'hiding' it is not a defense.
- ›Each deploy can create a new, untested endpoint: the surface changes every week.
- ›Authorization flaws generate no error and no exception log: the system works 'correctly' and hands over the wrong data.
- ›The damage is immediate and quantifiable in reais, not just in reputation.
The five threats that most often bring fintechs down
1. Authorization abuse and breakage in APIs (BOLA/IDOR)
BOLA (Broken Object Level Authorization), known by the older acronym IDOR (Insecure Direct Object Reference), is the number one flaw in the OWASP API Security Top 10. It occurs when an endpoint correctly identifies who the user is (authentication) but doesn't verify whether that user has rights over the specific object being requested (object-level authorization). In practical terms: the authenticated user requests /api/statement?account=1042 and receives the statement. They switch to account=1043 and receive another customer's statement. There was no intrusion, no password breaking, no exploit. The system simply handed it over, because nobody asked 'who does this account belong to?'. What makes BOLA so dangerous in fintech is the combination of maximum impact (the entire customer base) and total silence: every request is legitimate and successful (HTTP 200), triggers no error alert, and can run for months — until it becomes a headline.
Why BOLA slips past traditional tests
Automated scanners and WAFs look for attack patterns (injection, malicious payloads). A BOLA attack has no malicious payload — it's a perfectly formed request, with a valid token, simply asking for an identifier it shouldn't. Only a test that understands the business logic and the relationship between user and object finds this flaw. That's why manual API pentesting is irreplaceable here.
2. Data breaches and 3. Transactional fraud
Beyond BOLA, fintechs leak data through excessive data exposure (the API returns more fields than the client needs, and the app only hides them on screen — but the data is in the JSON response), through administrative endpoints exposed without authentication, through logs that record sensitive data in clear text, and through misconfigured buckets and databases. Under the LGPD, any of these scenarios constitutes a security incident involving personal data. In transactional fraud, on the other hand, the adversary doesn't steal data: they abuse logic. Manipulation of values in requests, race conditions that allow spending the same balance twice, bypassing limits, and abuse of refund and cashback flows. These are business logic flaws that no scanner detects because there's no classic technical vulnerability — there's a business rule that can be bent.
4. Key compromise and 5. Supply chain
API keys for payment gateways, database credentials, cloud provider tokens, and JWT signing keys are the crown jewels. When they leak — in a public repository, in an exposed environment variable, in a log — the attacker gains legitimate access, indistinguishable from authorized access; it's the preferred vector for anyone looking to escalate to ransomware or drain accounts. Supply chain risk, in turn, comes from dependencies: fintechs build fast on top of third-party libraries, and a compromised dependency or a malicious version published in a package repository places hostile code inside the trust perimeter. The attack doesn't come from outside through the door — it already came in with the build.
Quick exposure map for your fintech
- ✓Does every endpoint that returns a customer's data validate that the customer owns the requested object?
- ✓Do API responses contain only the necessary fields, or do they dump the entire database object?
- ✓Is there any secret, key, or credential committed in the repository history?
- ✓Is there rate limiting and detection of sequential identifier enumeration?
- ✓Do dependencies have an inventory (SBOM) and continuous scanning for known vulnerabilities?
- ✓Is there an audit trail that records 'who accessed whose object'?
Is fintechs data already exposed or up for sale? Find out now — for free.
Sem cartão, sem compromisso. Descubra em minutos o que já vazou da sua empresa e qual é o seu risco real.
The core angle: anatomy of an IDOR that exposes statements
Let's get to the concrete mechanism, because understanding the anatomy of exploitation is what separates a theoretical defense from a real one. Imagine a fintech with an endpoint that serves the logged-in user's statement. The first, naive version receives the account ID as a parameter and trusts it. The developer thought: 'the app only sends the user's own ID'. But the app is just a client; anyone with an account's token can call the API directly with any ID.
Step by step of the exploitation
First, the attacker creates a legitimate account and observes the app's traffic — they see that the app calls GET /v1/accounts/8810042/statements with their token. Second, they notice that the ID 8810042 is sequential and predictable. Third, they change the number: /v1/accounts/8810041/statements. If the server doesn't verify object ownership, it returns the statement of customer 8810041 — a different person. Fourth, the attacker automates it: a script walks through IDs from 1 to several million, downloading statements in bulk. In hours, they exfiltrate the entire base. No password was broken; every request returned HTTP 200; nothing in the application flagged an error.
The detail that decides everything
The fix is not to 'hide' the ID or make it random (UUID). A UUID makes enumeration harder, but doesn't fix the flaw: if the attacker discovers a valid UUID by another route, they can still access someone else's data. The real fix is authorization verification on the server: before returning the statement for account X, the backend asks 'does account X belong to the user of this token?'. Without that question, any obfuscation is merely cosmetic.
This is exactly the kind of reasoning that Decripte's API pentesting applies: it's not enough to find 'a vulnerability', you have to prove the exploitation end to end, demonstrate the impact (extract a statement that doesn't belong to the tester), and deliver the architectural fix — not just the superficial patch. Finding the IDOR before the attacker is the difference between a pentest report and an incident notification to the ANPD.
How Decripte's pentest finds the flaw before the attacker
Our fintech pentest is conducted with an explicit focus on APIs and business logic, because that's where the risk lives. We work from the OWASP API Security Top 10 as a methodological basis, but we go beyond the checklist: we map the relationship between users and objects, create multiple test identities, and systematically try to access one identity's objects using another's token. This 'multi-tenant adversarial' approach is what reveals BOLA, BOPLA (object property-level authorization flaw), and function-level authorization (BFLA).
What we specifically test in a fintech
Typical API pentesting scope
- ✓Object-level authorization on all endpoints that return customer data (BOLA/IDOR).
- ✓Function-level authorization: can a regular user call administrative endpoints?
- ✓Excessive data exposure: does the response deliver sensitive fields that the app hides in the UI?
- ✓Mass assignment: can the client alter fields it shouldn't (e.g., setting its own balance or role)?
- ✓Transactional logic flaws: race conditions, value manipulation, bypassing limits.
- ✓Authentication security: token strength, expiration, refresh, possibility of forging a JWT.
- ✓Rate limiting and protection against sequential ID enumeration.
- ✓Exposure of secrets in responses, headers, error messages, and app code.
Every finding comes with a reproducible proof of concept, severity classification, impact in executive language, and the recommended fix at the right level — architectural when the problem is by design, and pinpoint when it's an implementation issue. We don't deliver a scanner PDF; we deliver a remediation plan prioritized by real business risk.
One-off pentest versus continuous program
An annual pentest photographs the security of a single day. But a fintech does dozens of deploys per month, and each deploy can introduce a new endpoint. That's why we recommend recurring pentesting coupled with continuous vulnerability management — the photo becomes a film. The risk that matters is not what existed at the last audit; it's what went into production yesterday.
When the flaw slips through: Decripte's incident response
No defense is perfect. Part of security maturity is assuming an incident will happen and being ready for it to be short, contained, and well documented — instead of long, leaking, and silent. This is where Decripte's 24x7 SOC and Incident Response change the outcome. When a BOLA is being exploited in production, the signature shows up in monitoring: a single token hitting thousands of sequential objects, an anomalous volume of large responses, an enumeration pattern. The SOC detects the abuse even when the application thinks everything is normal.
The clock that matters: containment within 1 hour
In a fintech incident, every minute costs data and money. Our containment SLA of up to one hour exists because exfiltration damage is cumulative: containing in 40 minutes versus containing in 8 hours can be the difference between 5,000 records and the entire base; between a controlled notification to the ANPD and a public crisis. Containment doesn't wait for root cause — it stops the bleeding first (blocking the abusive token, emergency rate limiting, disabling the endpoint) and investigates in parallel.
The costliest mistake in incident response
Wiping everything and 'going back to normal' before understanding what happened. Without preserving evidence (logs, requests, timeline), you don't know the scope of the breach — and the LGPD requires you to know it in order to correctly notify the ANPD and the data subjects. Decripte contains without destroying the evidence, ensuring that recovery is informed by forensic investigation.
What would an incident in fintechs cost? See your real risk before it happens.
Sem cartão, sem compromisso. Descubra em minutos o que já vazou da sua empresa e qual é o seu risco real.
Structuring a continuous API security program
Fixing an IDOR is tactical. Ensuring that the next endpoint is born secure is strategic. Decripte helps fintechs build the program that turns security from an isolated event into a permanent capability. That means integrating authorization verification into the development cycle, instrumenting the right observability, keeping a live API inventory, and closing the loop between finding, fixing, and validating.
Compliance as a byproduct, not as the goal
Fintechs live with a dense set of requirements: PCI-DSS when they process card data; LGPD across all personal data operations; the Central Bank resolutions applicable to payment institutions and to those operating in the payment arrangement, including cybersecurity policy requirements; and frequently ISO 27001 and SOC 2 as a requirement from partners and investors. The good news is that a well-built API security program satisfies most of these requirements as a natural byproduct — compliance stops being a race against the audit and becomes the documented reflection of controls that already work.
Regulatory map summary for fintechs
- ›PCI-DSS: mandatory for anyone who stores, processes, or transmits card data.
- ›LGPD: governs all processing of personal data; incidents require notification to the ANPD and to data subjects within a reasonable timeframe.
- ›Central Bank: payment institutions and arrangement participants have cybersecurity and incident management requirements.
- ›ISO 27001 and SOC 2: not law, but frequently required by partners, acquirers, and investors.
Why acting early is cheaper than reacting late
There's a brutal cost asymmetry in fintech security. Finding and fixing a BOLA in a pentest costs a fraction of what the same BOLA costs when exploited in production: forensic investigation, notification to the ANPD, notifying thousands of data subjects, press exposure, customer churn, possible regulatory sanction, and the product team's paralysis during the crisis. Preventive security is not a cost center — it's the cheapest policy a fintech can buy.
The virtuous cycle we recommend
Start with the free Threat Management diagnostic at decripte.com.br/intelligence-center to see your external exposure. Next, an API pentest focused on authorization reveals the flaws that matter. The 24x7 SOC ensures that if something slips through, it will be detected in real time. Vulnerability management keeps the exposure window short. And the compliance structure turns all of this into a commercial differentiator. Each piece reinforces the next.
To get started, talk to Decripte at decripte.io/start or through the form at /contato. We assess your API architecture, prioritize risks by real business impact, and map the path from diagnostic to continuous program.
Anatomy of an IDOR in statements — real, anonymized example
Real, de-identified example
Real, anonymized example (without identifying the customer). A digital-account fintech in rapid growth exposes a public API for its mobile app. One of the endpoints serves the account statement based on a sequential numeric identifier passed in the URL. The team, lean and focused on shipping features, assumed that 'the app only sends the user's own ID' and did not implement object ownership verification on the backend. The flaw is a classic BOLA/IDOR: authentication present, object-level authorization absent.
Detection
Decripte's 24x7 SOC, monitoring the API, fires an alert: a single authentication token is requesting statements for thousands of different account IDs, in sequential order, within a few minutes. The enumeration pattern and the anomalous volume of large responses don't match legitimate human use. The application, for its part, records only successful HTTP 200 requests — no error, no alarm of its own. It's the SOC's intelligence that sees the abuse behind the 'success'.
Containment
Within the SLA of up to 1 hour, the response team executes layered containment: immediate blocking of the abusive token, application of emergency rate limiting on the endpoint, and, in coordination with the fintech's team, temporary disabling of the statement route while the fix is prepared. The data bleeding is staunched without taking down the rest of the operation. Evidence (request logs, timeline, accessed IDs) is preserved for the investigation.
Eradication
The root cause is fixed at the right level: implementing object-level authorization verification on the backend — before returning any statement, the server validates that the requested account belongs to the token's user. Decripte audits neighboring endpoints and finds the same failure pattern in three other routes (transactions, receipts, registration data), fixing them all. Enumeration detection and structural rate limiting are added.
Recovery
With the fix validated by retesting, the endpoint goes back online in a controlled manner. From the preserved evidence, Decripte helps the fintech determine the exact scope of what was exposed — which accounts, which data — essential information to meet the LGPD obligations of notifying the ANPD and the affected data subjects, and for any reporting required by the Central Bank.
Lessons
The incident becomes a program. Recurring API pentesting focused on authorization is deployed, authorization verification is integrated into the development pipeline (so that the next endpoint is born secure), and the SOC begins maintaining permanent enumeration detection signatures. Compliance is documented as evidence of the new controls.
Outcome with Decripte
What could have been the silent exfiltration of the entire base over weeks — with a headline, sanction, and churn — was contained in under an hour from detection. The fintech comes out not only with the flaw fixed, but with a continuous API security program, 24x7 monitoring, and an evidence trail that supports its regulatory posture. The difference wasn't luck: it was the combination of real-time detection, fast containment, and architectural fix. Ideally, that same IDOR would have been found earlier, in a pentest — and that's exactly why we recommend starting with the diagnostic at decripte.com.br/intelligence-center.
Don’t wait for the incident. Start hardening fintechs today.
Comece pelo diagnóstico gratuito agora e veja em minutos o que já vazou. SOC 24x7 e contenção em até 1h nos planos pagos.
How Decripte responds to incidents in fintechs
When an incident hits a fintech, the priority is to staunch the financial and data damage before it escalates, without destroying the evidence needed for the investigation and for regulatory obligations. Our process is structured into phases that run in parallel whenever possible.
- Detection and triage: the 24x7 SOC identifies the sign of abuse (enumeration, anomalous volume, exfiltration pattern) even when the application reports 'success', and classifies the severity in minutes.
- Layered containment within the SLA of up to 1 hour: blocking the abusive token or origin, emergency rate limiting, and isolation or disabling of the affected endpoint, stopping the bleeding first.
- Evidence preservation: logs, requests, accessed IDs, and timeline are preserved before any cleanup, ensuring that the scope of the incident can be determined precisely.
- Root cause eradication: fix at the right level (object-level authorization on the backend, not cosmetic obfuscation) and scanning of neighboring endpoints with the same failure pattern.
- Validated recovery: the service goes back online in a controlled manner, with the fix confirmed by retesting and permanent detections deployed.
- Scope determination and regulatory support: from the evidence, we determine exactly which data was exposed, the basis needed for notification to the ANPD and the data subjects (LGPD) and for reporting to the Central Bank when applicable.
- Executive and technical report: delivery of a post-incident report with timeline, root cause, impact, and a prioritized remediation plan.
- Transformation into a program: the lessons become permanent controls — recurring pentesting, continuous monitoring, and security fixes integrated into development.
How we structure a fintech's security
Fintech security is not a product you install; it's a program you maintain. Decripte organizes this program into pillars that reinforce each other, from diagnosing exposure to continuous API governance.
API security by design
Object-level authorization verification (anti-BOLA/IDOR) and function-level authorization as a non-negotiable requirement of every endpoint that touches customer data or money. We integrate this validation into the development cycle so that each deploy is born tested, not vulnerable.
Recurring pentesting focused on authorization and logic
Multi-tenant adversarial tests that try to access one user's object with another's token, combined with business logic exploitation (race conditions, value manipulation, mass assignment). Reproducible proofs of concept and architectural fixes, not just a scanner list.
24x7 detection and fast response
SOC monitoring abuse patterns in real time — enumeration, exfiltration, anomalous token use — coupled with an incident response plan with a containment SLA of up to 1 hour that stops the damage before investigating the cause.
Continuous vulnerability and secrets management
Short exposure window: continuous vulnerability scanning, dependency inventory (SBOM) for supply chain risk, and treating keys and secrets as critical assets — vault, rotation, and no credentials in code or logs.
Structured compliance
Controls designed to satisfy PCI-DSS, LGPD, applicable Central Bank requirements, and frameworks such as ISO 27001 and SOC 2 as a byproduct of secure operation — turning regulatory requirements into a commercial differentiator and audit readiness.
Recommended plans for Fintechs
Pentest
Finds the BOLA/IDOR, the authorization flaws, and the transactional logic abuses before the fraudster, with proof of concept and architectural fix — the most cost-effective control for a fintech with public APIs.
See plan →SOC 24x7
Detects API abuse in real time (enumeration, exfiltration, anomalous token use) even when the application reports 'success', ensuring that a flaw that slipped past the pentest doesn't run silently for months.
See plan →Vulnerability Management
Keeps the exposure window short in an environment that changes with every deploy, covering vulnerabilities, leaked secrets, and supply chain risk in third-party dependencies.
See plan →Compliance
Structures PCI-DSS, LGPD, and the Central Bank requirements as a byproduct of real controls, converting regulatory obligation into a commercial differentiator before partners and investors.
See plan →Frequently asked questions
What is the biggest security vulnerability in fintechs?
By impact, it's the authorization flaws in APIs — especially BOLA/IDOR, the number one in the OWASP API Security Top 10. They allow an authenticated user to access another customer's data or transactions without 'breaking' anything: the system simply hands over the wrong data. They're dangerous because they have maximum impact (the entire customer base) and total silence (every request returns success, with no error or alarm).
What is an IDOR and why is it so critical for a fintech?
IDOR (Insecure Direct Object Reference), today classified as BOLA, is when an endpoint correctly identifies the user but doesn't verify whether they have rights over the specific object requested. In a fintech, this means that changing the account ID in the URL can return another person's statement. It's critical because it exposes sensitive financial data at scale, constitutes an incident under the LGPD, and can be automated to exfiltrate the entire base in hours.
Is an annual pentest enough for my fintech?
Usually not. Fintechs do multiple deploys per week, and each deploy can introduce a new, untested endpoint. An annual pentest photographs the security of a single day; the real risk is in what went into production afterward. We recommend recurring pentesting coupled with continuous vulnerability management and 24x7 monitoring — the photo becomes a film.
How does Decripte detect an attack that returns only 'successful' HTTP 200 responses?
The 24x7 SOC doesn't just look at errors — it looks at behavior patterns. A single token hitting thousands of sequential identifiers, an anomalous volume of large responses, or exfiltration patterns are detected as abuse even when the application considers everything normal. The intelligence lies in recognizing the abuse behind the 'success'.
Which standards and regulations does my fintech need to meet?
It depends on the operation, but the typical set includes PCI-DSS (if it processes card data), LGPD (all processing of personal data, with obligations to notify the ANPD in incidents), and the cybersecurity and incident management requirements of the Central Bank applicable to payment institutions and arrangement participants. ISO 27001 and SOC 2 are not law, but are frequently required by partners and investors. Decripte structures these controls in an integrated way.
What should I do in the first minutes of a data breach?
Contain without destroying evidence. The instinct to 'wipe everything and go back to normal' destroys the logs needed to determine the scope of the breach — and the LGPD requires you to know the scope in order to correctly notify the ANPD and the data subjects. Decripte's incident response staunches the bleeding (blocking the token, rate limiting, isolating the endpoint) within the SLA of up to 1 hour, preserving the evidence in parallel. Reach out at decripte.io/start or /contato.
Does using a UUID instead of a sequential ID fix the IDOR?
No. A UUID makes enumeration harder, but doesn't fix the flaw: if the attacker obtains a valid UUID by another route, they can still access someone else's data. The real fix is object-level authorization verification on the server — before returning the data for account X, the backend validates that X belongs to the token's user. Any obfuscation without that verification is merely cosmetic.
Where do I start assessing my fintech's security?
With the free Threat Management diagnostic at decripte.com.br/intelligence-center, which shows your external exposure. From there, an API pentest focused on authorization reveals the flaws that matter, and we map the path to a continuous program. To hire or talk, use decripte.io/start or the form at /contato.
Sector terms
- BOLA / IDOR
- Broken Object Level Authorization (old acronym IDOR — Insecure Direct Object Reference): a flaw in which an endpoint authenticates the user but doesn't verify whether they have rights over the specific object requested, allowing access to other customers' data or transactions. It's the number one in the OWASP API Security Top 10.
- OWASP API Security Top 10
- A reference list maintained by the OWASP project with the ten most critical risks specific to APIs, used as the methodological basis of Decripte's API pentesting.
- Excessive Data Exposure
- When the API returns more fields than the client needs and the app only hides the excess on screen; the sensitive data is present in the response and can be read directly, constituting a breach.
- Containment SLA
- A commitment to a maximum time to staunch the damage of an incident after its detection. At Decripte, containment occurs within 1 hour, stopping the bleeding before completing the root cause investigation.
- SBOM
- Software Bill of Materials: an inventory of a system's dependencies and components, essential for assessing and responding to supply chain risks when a third-party library is compromised or has a known vulnerability.
- PCI-DSS
- Payment Card Industry Data Security Standard: a set of security requirements mandatory for organizations that store, process, or transmit payment card data.
Decripte protects and responds to incidents in fintechs.
Pentest, 24x7 SOC, incident response with a 1-hour containment SLA and compliance — without building an internal team. Or start free by seeing what has already leaked from your company.