api-security-top10

name

api-security-top10

description

OWASP API Security Top 10 as a dedicated API-only checklist -- BOLA, BFLA, broken object-property-level authz/mass assignment, unrestricted resource consumption, unsafe business-flow access, security misconfiguration, improper inventory management (shadow/zombie APIs), unsafe third-party API consumption, plus GraphQL/gRPC/SOAP/WebSocket coverage. Converted from master-pentest-prompt.md Phase 33. Use on API-only targets (no traditional web UI) as the dedicated checklist -- for mixed web+API targets the vuln-class skills already cover most of this ground per-endpoint.

OWASP API Security Top 10 (dedicated -- API yes, plain web no)

When to use

API-only targets, run per endpoint and per HTTP method, both authenticated and unauthenticated. On a mixed web+API target, the individual vuln-class skills (access-control-and-idor, ssrf, etc.) already cover most of this per-endpoint -- this skill is for treating the API surface as its own dedicated pass, and for the API-specific items (schema extraction, inventory management) those skills don't otherwise name.

The ten items

• BOLA (Broken Object Level Authorization): object IDs accessible across users via UUID, sequential ID, or enum -- check nested objects and deep-linked resources too, not just the top-level ID.
• BFLA (Broken Function Level Authorization): a lower-privilege role successfully calling an admin-only function.
• Broken Object Property Level Authorization: mass assignment or read-only field tampering (role: admin, balance: 0, verified: true) sent in a request body the client shouldn't be able to set.
• Unrestricted Resource Consumption: no rate limit, no size limit, no query-depth limit, no pagination cap, multi-query DoS via a single expensive request.
• Broken Function Level Auth: missing authentication entirely on endpoints that should require it.
• Unrestricted access to sensitive business flows: change, transfer, or refund operations executable without proper step-up verification.
• SSRF (see the ssrf skill for the general technique) and server-side XSS via API responses that get rendered into HTML somewhere downstream.
• Security misconfiguration: default or overly permissive CORS, verbose error bodies, unnecessary HTTP methods left enabled, missing TLS on an API subdomain specifically.
• Improper Inventory Management: old/unversioned endpoints still live, shadow APIs shipped from stale code paths, non-production endpoints reachable publicly.
• Unsafe consumption of APIs: the target calling third-party APIs without validating their responses, letting an upstream compromise become the target's own vulnerability.

Protocol-specific coverage

GraphQL (introspection left enabled, batching abuse -- see deep-cut-surfaces for the fuller GraphQL list), gRPC (see microservices-and-internal-api for reflection/proto-leak detail), SOAP/XML (XXE -- see the xxe skill), WebSocket subscriptions with no auth check, and importer/webhook features that follow an attacker-supplied URL.

Schema-driven fuzzing

Pull the OpenAPI/Swagger schema (see misc-deep-cuts for exposure paths like /swagger-ui, /redoc) and fuzz every defined operation from it. Test both idempotent and non-idempotent verbs, and check any endpoint touching PII specifically for its inter-consumer-security (ICS) logic.