API Security Explained: The OWASP Risks Every Backend Team Should Know
API security failures are often business-logic and authorization failures, not exotic cryptography bugs. The current OWASP API Security Top 10 remains the 2023 edition and is a useful map of where teams should focus.
1. Object-Level Authorization
If a request contains an object ID, verify the caller may access that exact object.
GET /invoices/9182
A valid login does not grant access to every invoice.
2. Broken Authentication
Protect login, token/session lifecycle, recovery, MFA flows, credential storage, and brute-force-sensitive endpoints. Do not invent custom authentication protocols when mature standards/libraries exist.
3. Object Property Authorization
Avoid both excessive data exposure and unsafe mass assignment.
The backend should explicitly decide which fields a caller may read and modify, instead of binding arbitrary request JSON directly to privileged model properties.
4. Resource Consumption
Limit request frequency and expensive dimensions such as body size, page size, batch size, concurrent work, uploads, OTP attempts, and paid third-party calls.
5. Function-Level Authorization
Administrative or privileged endpoints need explicit permission checks even if their URLs are hard to guess or hidden from the UI.
6. Sensitive Business Flows
Some abuse is valid API usage performed at abusive scale—for example automated reservation hoarding, coupon abuse, ticket purchasing, or account creation.
Protect the business workflow, not only the endpoint.
7. SSRF
APIs that fetch user-controlled URLs can be abused to reach internal or cloud-metadata services. Restrict outbound destinations and protocols and validate resolved addresses.
8. Security Misconfiguration
Remove debug endpoints/default credentials, restrict CORS and methods, patch components, return safe errors, and keep unnecessary services off public networks.
9. API Inventory
Know which hosts, versions, staging APIs, legacy routes, and documentation endpoints are deployed. An abandoned old API can bypass controls added to the current version.
10. Unsafe Third-Party API Consumption
Treat data from partner/vendor APIs as untrusted. Validate responses, use TLS, bound redirects/timeouts, and do not assume another company's API cannot be compromised.
Final Takeaway
API security is mostly about maintaining trust boundaries across identity, objects, properties, functions, resources, and integrations. Use the OWASP list as a threat-model checklist, then test the exact business rules your API exposes.
References
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