Payment API abuse
Transaction replay, negative amount injection, race conditions in balance updates, duplicate submission through API inconsistencies, and idempotency key manipulation. Manual testing only — no automated tool tests these.
pentest · fintech
Penetration testing for fintech companies.
Payment APIs, transaction processing logic, and cardholder data environments under active attack. PCI DSS Requirement 11.3 requires it annually. We scope fintech engagements around the real attack surface: payment flows, business logic, CDE boundary, and the API layer between your platform and the financial system.
01. attack surface
What attackers target in fintech.
Financial platforms attract sophisticated adversaries. Business logic and payment flow abuse are rarely caught by scanners.
Business logic flaws
Referral bonus stacking, promo code abuse, limit bypass, rounding error exploitation at scale, currency conversion discrepancies, and transaction ordering attacks. The dollar impact of these findings is often quantifiable directly.
Account takeover paths
Credential stuffing against login and password reset endpoints, MFA fatigue and bypass, session token predictability, and insecure "remember me" implementations. High-value accounts are targeted disproportionately.
PCI scope creep
Cardholder data found outside the defined CDE: in application logs, error messages, payment page JavaScript, webhook payloads, and analytics integrations. Scope creep nullifies segmentation claims.
Open Banking and PSD2 APIs
OAuth2 consent flow manipulation, token scope elevation, insufficient redirect_uri validation, and excessive data exposure in AISP and PISP API responses.
Third-party processor integrations
SSRF via payment processor callbacks, insecure iframe embedding, Magecart-style JavaScript injection points, and insecure storage of processor credentials in your application layer.
02. compliance
Regulatory requirements for fintech.
Fintech carries more regulatory requirements per product surface than almost any other vertical. Penetration testing appears in all of them.
- PCI DSS v4.0 Requirement 11.3Annual internal (Req 11.3.1) and external (Req 11.3.2) penetration test of the CDE and connected systems. Segmentation test required if you rely on network isolation to reduce your scope. ASV scans are not a substitute for penetration testing. PCI DSS pentest details →
- SOC 2 Type IIInstitutional clients, enterprise customers, and investors expect it. Trust Services Criteria CC6.1, CC6.6, and CC7.1 all reference technical safeguard testing. The pentest report feeds multiple controls in the evidence package. SOC 2 pentest details →
- NY DFS Part 500Required for entities licensed or registered in New York State. §500.05 requires annual penetration testing and bi-annual vulnerability assessment. Non-compliance is a civil enforcement risk under DFS supervision.
- GLBA and FFIECFor US fintech handling consumer financial data. The FFIEC IT Examination Handbook includes explicit penetration testing expectations for financial institutions and their service providers. The FTC Safeguards Rule requires periodic pen testing for non-bank financial institutions.
03. scope
What we test in a fintech pentest.
Scope is agreed on the scoping call and documented in the SOW. CDE boundary is cross-checked against your scoping documentation before testing starts.
Payment flows end to end
From initiation through settlement. Covers the full transaction lifecycle — authorization, capture, refund, chargeback — for manipulation and race condition opportunities.
CDE boundary
We cross-check your CDE scoping documentation against what we observe in the application. Systems touching cardholder data that are out of your defined scope are flagged immediately.
Business logic
Transaction limits, balance checks, referral systems, currency conversion, fee calculation, rounding. Manual testing only — business logic flaws are invisible to scanners.
APIs
REST payment APIs, Open Banking endpoints, webhook receivers, and internal service-to-service calls. OWASP API Top 10 aligned. Authentication and authorization across every endpoint.
Web and mobile apps
Payment flows in your web app and mobile app. Client-side manipulation, certificate pinning on mobile, secure storage of payment tokens, and PCI-relevant JavaScript on checkout pages.
Network segmentation
If you rely on network segmentation to reduce PCI scope, we validate it holds under adversarial conditions — the segmentation test required under PCI DSS v4.0 Req 11.3.4.
04. deliverables
What you walk away with.
Structured for your QSA, your engineering team, and your auditor.
PCI DSS Req 11.3 report
Internal and external test documented separately, as required. CDE scoping, segmentation validation results, and finding catalog. Structured to meet QSA evidence requirements.
Business logic finding catalog
Each finding documented with proof-of-concept and quantified business impact. Not just CVSS — what's the maximum dollar exposure per transaction, per account, or at scale?
Retest within 30 days
Post-fix re-validation from the same engineer. Each finding marked resolved, partially resolved, or open. Retest report issued for QSA evidence package.
Attestation letter
Signed by the named engineer. States methodology, CDE scope reference, dates, and retest outcome. Ready for QSA and SOC 2 auditor review.
05. faq
Questions before the call.
Do you have PCI DSS penetration testing experience?
Yes. We scope to the CDE, document segmentation boundaries, and deliver in the format QSAs expect: internal and external test results, scoping documentation, and a segmentation test if you rely on isolation to reduce scope.
What's the difference between an ASV scan and a penetration test?
ASV scans are automated vulnerability scans of external-facing systems — required quarterly under Requirement 11.3.2 but separate from the penetration test. Penetration testing is manual exploitation, chained findings, and CDE boundary verification. Both are required. They are not interchangeable.
Do we need both internal and external testing?
Yes, under PCI DSS v4.0. Requirement 11.3.1 covers internal testing of the CDE. Requirement 11.3.2 covers external testing of internet-facing components connected to or supporting the CDE. Both are required annually.
Can you test our payment processor integration?
Yes, for the parts within your system boundary. The processor's own infrastructure is out of scope — they handle their own compliance. The integration layer on your side — API calls, webhook receivers, iframe embeds — is in scope.
We use a hosted payment page — does that reduce our scope?
Possibly, but the scoping decision belongs to your QSA, not your payment vendor's sales team. We help you document the boundary and test the integration points. Scope reduction claims need to be verified, not assumed.
Ready to scope a fintech pentest?
30-minute scoping call covers your CDE boundary, your QSA timeline, and the scope your auditor expects. Free.