offensive-api-security

Offensive API Security Testing

You are conducting authorized security assessments against API-driven applications. This skill covers REST, gRPC, and WebSocket attack surfaces with emphasis on the OWASP API Security Top 10 2023. Every technique assumes you have written authorization and a defined scope. Your goal is to identify vulnerabilities that allow unauthorized data access, privilege escalation, or service disruption through API-layer attacks.

Quick Workflow

1. Map the API surface: collect OpenAPI/Swagger specs, gRPC reflection output, and WebSocket endpoints.
2. Enumerate authentication mechanisms: API keys, OAuth flows, JWTs, session tokens.
3. Test BOLA/IDOR by substituting object identifiers across authenticated contexts.
4. Probe authorization boundaries with BFLA checks across roles and HTTP methods.
5. Fuzz parameters for mass assignment, content-type switching, and verb tampering.
6. Assess rate limiting and resource consumption controls.
7. Test gRPC-specific vectors: reflection enumeration, metadata injection, protobuf manipulation.
8. Evaluate WebSocket security: origin validation, message integrity, CSWSH.
9. Check for SSRF via URL-accepting parameters and webhook configurations.
10. Document findings with reproduction steps and severity ratings.

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OWASP API Top 10 2023 -- BOLA and IDOR

Broken Object Level Authorization (BOLA) is the most prevalent API vulnerability. You test it by capturing a legitimate request containing an object identifier and replaying it with identifiers belonging to other users or tenants.

GET /api/v1/users/1001/orders HTTP/1.1
Authorization: Bearer eyJhbGciOi...user_a_token
Host: target.example.com

Replay with a different user ID while retaining the original token:

GET /api/v1/users/1002/orders HTTP/1.1
Authorization: Bearer eyJhbGciOi...user_a_token
Host: target.example.com

Automate IDOR testing across sequential and UUID-based identifiers:

# Sequential ID enumeration
for id in $(seq 1000 1050); do
  status=$(curl -s -o /dev/null -w "%{http_code}" \
    -H "Authorization: Bearer $TOKEN_A" \
    "https://target.example.com/api/v1/users/${id}/orders")
  echo "ID: ${id} -> HTTP ${status}"
done