Broken object-level authorization is still the number-one API risk — here's what to fix first.
API Security Best Practices for Fintech Teams: The OWASP-Aligned Guide
A practical guide to securing fintech APIs against the OWASP API Security Top 10, starting with authorization flaws and inventory gaps.
Fintech APIs move money and personal financial data, which makes them a high-value target. The OWASP API Security Top 10 (2023 edition, still current in 2026) is the industry-standard reference for what to prioritize.
Top risks to close first
Broken Object Level Authorization (BOLA) — The #1 risk: an API fails to verify that the requesting user actually owns the object/resource being accessed, letting an attacker pull another user's data by changing an ID.
Broken Authentication — Weak token handling, missing rate limits on login endpoints, or predictable session tokens that let attackers impersonate users.
Broken Object Property Level Authorization (BOPLA) — A 2023-introduced category merging the old "Excessive Data Exposure" and "Mass Assignment" risks: APIs returning or accepting more fields than a client should see or set.
Unrestricted Resource Consumption — APIs without limits on request size, rate, or cost, enabling denial-of-service or excessive infrastructure spend.
Broken Function Level Authorization — Regular users able to call admin-only endpoints because role checks aren't enforced server-side.
Practices that hold it together
Maintain a live API inventory — You cannot secure what you don't know is running; shadow and deprecated ("zombie") endpoints are a common breach vector.
Treat third-party responses as untrusted input — Validate and sanitize data coming back from partner or vendor APIs exactly as you would user input.
Enforce authorization at the object level, every request — Don't rely on obscurity (hard-to-guess IDs); check ownership server-side on every call.
Rate-limit and monitor for abuse — Unrestricted resource consumption enables both DoS and unexpected cloud cost spikes.
Guard sensitive business flows — A newer OWASP category flags APIs that expose sensitive flows (e.g., bulk purchasing, account creation) to automated abuse without behavioral controls.
Sources
Pynt: OWASP API Top 10 Complete Guide, F5: OWASP API Security Top 10 Overview.
Frequently asked questions
Broken Object Level Authorization happens when an API lets a user access another user's data or resource by simply changing an ID in the request — it's ranked #1 because it's common, easy to exploit, and often invisible to firewalls.
No — as of mid-2026, the 2023 edition is still the current, authoritative OWASP API Security Top 10; organizations should keep using it until OWASP publishes an update.
You cannot apply authorization checks, rate limits, or patches to an endpoint you don't know exists — shadow and zombie APIs are a leading cause of breaches precisely because they're unmonitored.