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NoorQureshiNoorQureshi/ronin/skills/api/api-bola/SKILL.md

api-bola

Skill26 starsChanged 32 days agoMITView on GitHub

Broken Object/Function Level Authorization in REST/JSON APIs (the #1 API risk). Load on any REST API with object ids in paths/bodies (/api/v1/users/123, /orders/{id}), Bearer auth, mobile-app backends, or admin vs user function separation. Signals: predictable ids, verbs that skip re-authorization, "role" enforced only in the UI.

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SKILL.md

Broken Object/Function Level Authorization (BOLA/BFLA)

When it applies

An API exposes objects (BOLA) or privileged functions (BFLA) and enforces authorization weakly. The API version of IDOR — but APIs multiply the surface (many endpoints, verbs, versions, and a mobile client that trusts the server less than the web UI does).

Why it works

APIs are stateless and object-centric; each endpoint must independently check "can this token act on this object/function?". Teams centralize authentication but scatter (or forget) authorization, and hide admin functions in the client instead of the server.

Method

  1. BOLA: with two tokens, request another user's object id on every endpoint & verb; also try guessing/incrementing ids and IDs leaked from list endpoints.
  2. BFLA: take an admin-only call (from JS, mobile, or docs) and replay it with a low-priv token; try method swaps (GET→PUT/DELETE) and hidden verbs the UI never issues.
  3. Version & shadow endpoints: /api/v1/ may lack fixes present in /v2/; /internal/, /debug/, Swagger/OpenAPI docs reveal ungoverned routes.
  4. Automate with Burp Autorize (low-priv token as the "enforcement" session) to flag every request that succeeds when it shouldn't.

Gotchas

  • 200 vs 403 is the tell, but some APIs return 200 with an empty body — diff the content.
  • IDs as UUIDs still leak via list/search endpoints and other objects' relations.
  • Rate-limit and WAF differ per API version — the vuln may only show on an older route.

Verify success

A low-privilege (or cross-tenant) token successfully reads/modifies an object or invokes a function reserved for another user/role.

References

OWASP API Security Top 10 (2023) API1/API5; PortSwigger access-control labs.

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