API Security Auditor

Overview

Performs a structured security audit of REST or GraphQL APIs against the OWASP API Security Top 10. Provides detection methods (code review + testing), authentication/authorization review, BOLA/IDOR testing procedure, injection point identification, rate limiting testing, and a professional audit report template with findings, risk ratings, and remediation recommendations.

When to Use This Skill

• Before launching a new API or major version.
• After significant changes to auth, authorization, or data access logic.
• As part of a security review or bug bounty prep.
• The user asks for an "API security audit" or "OWASP API Top 10 review".

Prerequisites

• Access to the API source code and/or a running instance (staging preferred).
• Authentication credentials or tokens for different roles/users (if testing with auth).
• Tools: Postman/Insomnia or curl, Burp Suite or ZAP (for proxying), or custom scripts.

Steps

1. OWASP API Top 10 2023 checklist (with detection method for each):

   • API1:2023 Broken Object Level Authorization (BOLA/IDOR)
   • API2:2023 Broken Authentication
   • API3:2023 Broken Object Property Level Authorization
   • API4:2023 Unrestricted Resource Consumption (rate limiting, DoS)
   • API5:2023 Broken Function Level Authorization
   • API6:2023 Unrestricted Access to Sensitive Business Flows
   • API7:2023 Server Side Request Forgery (SSRF)
   • API8:2023 Security Misconfiguration
   • API9:2023 Improper Inventory Management
   • API10:2023 Unsafe Consumption of APIs (third-party)

2. Authentication & session review:

   • JWT validation (alg, exp, signature, claims).
   • Token storage and transmission.
   • OAuth scopes and PKCE.
   • Password/reset flows.

3. Authorization testing (BOLA/IDOR):

   • Systematically change IDs in requests (user_id, order_id, document_id) while authenticated as different users.
   • Test horizontal (same role, different user) and vertical (lower role accessing higher).
   • GraphQL: test for missing authorization on every field/resolver.

4. Injection & input validation:

   • SQLi, NoSQLi, command injection in query params, body, headers.
   • Mass assignment / over-posting.
   • GraphQL: introspection enabled in prod? deep nesting DoS?

5. Rate limiting & resource limits:

   • Test with high volume from one IP / one user.
   • Check for per-user vs per-IP limits.
   • Look for expensive operations without limits (search, export, report generation).

6. Output:

   • Structured audit report (Markdown template) with:
     • Executive summary
     • Findings table (OWASP item | Severity | Location | Evidence | Recommendation)
     • Positive findings (what is done well)
     • Remediation roadmap
   • Specific test cases / curl commands used.
   • Code-level indicators to look for in reviews.

Examples

A complete audit report template filled with realistic findings for a typical REST + GraphQL API (BOLA on /users/{id}/orders, missing rate limit on search, JWT alg confusion, over-fetching in GraphQL, etc.) plus the exact test procedures and curl examples used to discover them is included.

Edge Cases & Error Handling

• Authorization logic in the client: Flag as critical — server must always enforce.
• GraphQL: Field-level auth, query cost analysis, depth limiting.
• Microservices: Auth must be validated at every service boundary (or use a service mesh with mTLS + auth).

Verification

1. The auditor follows the checklist and produces a report.
2. At least the critical/high findings have clear reproduction steps.
3. Code review confirms the vulnerable patterns exist (or the fix is in place).
4. Re-test after remediation — the issue is closed.
5. Success: The API has no critical OWASP API Top 10 issues, or they are explicitly accepted with compensating controls and timelines.

References

• OWASP API Security Top 10 2023
• OWASP Testing Guide
• GraphQL Security Cheat Sheet
• JWT Security