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+---
+name: api-security
+description: "Invoke this skill when the task is authorized offensive testing of a REST, GraphQL, WebSocket, or SOAP API beyond recon: authentication and authorization flaws (BOLA, IDOR, BFLA), JWT and OAuth weaknesses, GraphQL-specific abuse, input validation, business logic, rate-limit trust confusion, and excessive data exposure."
+---
+
+# API Security Testing (REST, GraphQL, WebSocket, SOAP)
+
+This is the hunting counterpart of api-recon. api-recon maps the API surface and stops; this skill attacks the mapped surface under an authorized engagement. The standing finding quality gates and the adversarial gate in your system prompt apply throughout, and an access-control finding only exists once a second account or role has proven the boundary is real.
+
+Attribution: adapted from the `api-security` playbook of [zhaoxuya520/reverse-skill](https://github.com/zhaoxuya520/reverse-skill) (MIT License).
+
+## Boundaries
+
+- Rate-limit and load tests only within the engagement's written impact budget. Most bounty programs forbid denial of service outright; volume that degrades the service for other users is out of bounds. Race-condition tests use a handful of concurrent requests, never load tools.
+- Do not exfiltrate real user data to prove a BOLA. One record you are authorized to touch, or your own second account, is sufficient evidence.
+- Destructive payloads (deletion, mass assignment on write endpoints) only against accounts and resources created for the test.
+- Every confirmed finding needs a replayable artifact: the exact request, the exact response, and the authorization context that produced it.
+
+## Phase checklists
+
+### Phase 1: discovery (handoff from api-recon)
+
+- Spec sources: `/swagger.json`, `/openapi.json`, `/api-docs`, `/graphql`, JS bundles, robots.txt.
+- Undocumented path brute force: ffuf or kiterunner with API wordlists.
+- GraphQL introspection, three tiers: the full introspection query; a trimmed query if the full one is blocked; minimal `__schema { types { name } }` as the last probe.
+
+### Phase 2: authentication
+
+JWT (jwt_tool or manual):
+
+- [ ] `alg: none`: header rewritten, signature stripped.
+- [ ] key confusion: RS256 public key accepted as an HS256 secret.
+- [ ] weak HMAC secret: dictionary attack (`jwt_tool -C -d wordlist.txt`).
+- [ ] expired or tampered claims: `exp`, `iat`, `sub`, `role`.
+- [ ] `kid` injection: path traversal inside the key id.
+
+OAuth 2.0:
+
+- [ ] `redirect_uri` manipulation leading to authorization-code theft.
+- [ ] missing `state` (CSRF on the authorization flow).
+- [ ] token leakage via `Referer` or platform logs.
+- [ ] missing PKCE on public clients.
+
+GraphQL auth:
+
+- [ ] mutation reachable through GET (CSRF).
+- [ ] batched queries bypassing per-operation authorization.
+
+### Phase 3: authorization (BOLA / IDOR / BFLA)
+
+BOLA, object level:
+
+- [ ] enumerate numeric ids: `/user/1` to `/user/2`.
+- [ ] enumerate UUIDs harvested from other responses.
+- [ ] substitute usernames or emails in paths and bodies.
+- [ ] two-session replay: user A's session requesting user B's objects (Burp Autorize or a manual response diff).
+
+BFLA, function level:
+
+- [ ] standard user calling admin endpoints.
+- [ ] HTTP method swap: GET to PUT, PATCH, DELETE.
+- [ ] version downgrade: `/v2/admin` to `/v1/admin`.
+- [ ] batch-operation injection: append an admin id to the bulk body.
+
+### Phase 4: GraphQL-specific
+
+- [ ] introspection exposing schema details it should hide.
+- [ ] alias overload (dozens of aliases in one query) and batched queries as compute amplification, within the impact budget.
+- [ ] field-suggestion error messages leaking schema names.
+- [ ] GraphiQL or a playground exposed unauthenticated.
+- [ ] deep nesting as a resource-exhaustion vector, within the impact budget.
+- [ ] trace or debug mode returning metadata.
+
+### Phase 5: REST input validation
+
+- [ ] HTTP method swap on every endpoint.
+- [ ] Content-Type tampering: JSON to XML to multipart (XXE where XML is accepted).
+- [ ] NoSQL operator injection: `{"username": {"$gt": ""}}`.
+- [ ] SSRF through URL-taking parameters (webhooks, avatar imports, fetchers).
+- [ ] HTTP parameter pollution: `?role=user&role=admin`.
+- [ ] mass assignment: `is_admin: true` added to request bodies.
+
+### Phase 6: business logic and differential testing
+
+- [ ] diff v1 against v2 of the same API: status-code changes, removed fields, latency regressions.
+- [ ] role matrix: admin, user, readonly through the same workflow.
+- [ ] coupon, credit, and price manipulation on test accounts.
+- [ ] TOCTOU races with a few concurrent requests.
+
+### Phase 7: WebSocket
+
+- [ ] endpoint discovery (upgrade handshakes).
+- [ ] message injection, prototype pollution through frames.
+- [ ] oversized-message handling.
+- [ ] type confusion in frame payloads.
+- [ ] cross-site WebSocket hijacking (CSWH).
+
+### Phase 8: rate-limit trust confusion
+
+- [ ] header spoofing: `X-Forwarded-For`, `X-Real-IP`, reported as a trust-boundary finding, never scaled into volume.
+- [ ] path variants: `/api/`, `/api`, `/Api/`, `/API/` bypassing a path-keyed limiter.
+- [ ] the finding is the bypass mechanism itself; do not demonstrate it under load.
+
+### Phase 9: data exposure
+
+- [ ] response fields beyond what the UI renders (diff the API response against the page).
+- [ ] pagination enumeration: `?page=1&limit=10000`.
+- [ ] error messages leaking stack traces, internal paths, or SQL.
+- [ ] GraphQL nested traversal reaching unauthorized data.
+- [ ] spec files exposing internal endpoints.
+
+### Phase 10: regression handoff
+
+- [ ] persist every confirmed finding as a replayable request (curl command or HAR artifact) so retests and the reporter can re-verify.
+- [ ] mark which findings are safe to re-run and which are one-shot (nonce or state dependent).
+
+## Tools
+
+| Tool | Use | Notes |
+|---|---|---|
+| curl + jq | request replay and diffing | always available |
+| jwt_tool | JWT attack automation | pip-installable; verify before use |
+| ffuf, kiterunner | endpoint brute force | verify container availability |
+| Burp Autorize, AuthMatrix | two-session authorization diffing | only where a Burp instance exists |
+
+The upstream playbook also names Vespasian, Entropy, Escape DAST, FireTail, and api.sh; treat those as references until verified in this environment, and prefer the manual checklists over unverified tooling.
+
+## Completion self-check
+
+- [ ] every executed phase produced artifacts (requests, responses, diffs) in the work dir.
+- [ ] each access-control finding was confirmed with a second session or role.
+- [ ] nothing in the report relies on a tool or output you did not actually run.