hunt-spa-api

---
name: hunt-spa-api
description: Discover a single-page-app's hidden backend API from its public JS bundle, then test that API for broken access control / missing authentication. One of the highest-yield web plays in modern recon — SPAs ship their entire backend route map to the browser, and the API behind them is frequently missing the auth middleware the login page implies. Built from an authorized engagement where this play found an unauthenticated financial API that an ASM scan reporting hundreds of "Criticals" completely missed. Use whenever a target serves a JS-heavy SPA (React/Vue/Angular/Next), an "app"/"console"/"dashboard"/"portal" subdomain, or any `*api*` host shows up in recon. Leaked build artifacts (source maps / .env / .git / asset-manifest) are owned by hunt-source-leak; API version-inventory and behavioral diffing by hunt-shadow-api; this skill owns mapping a live SPA's backend routes from its JS bundle and testing them for broken access control / missing auth.
sources: authorized-engagement
report_count: 1
---

## When to use this skill

Trigger when:
- A target host returns a tiny HTML shell + big `/static/js/*.js` or `/_next/static/*` bundles (React/Vue/Angular/Next/Svelte SPA)
- You see a subdomain named `console`, `app`, `dashboard`, `portal`, `admin`, `panel`, `manage`, `internal`
- Recon surfaces any `*api*`, `*-api*`, `api.*` host
- A login page is OAuth/SSO-gated (the *frontend* auth tells you nothing about whether the *API* enforces auth)

The core insight: **a SPA is a client to a backend API, and it ships the full map of that API — hosts, routes, sometimes keys — to anyone who views source.** The login page being protected says nothing about whether the API behind it checks tokens. Auth is frequently enforced on the *gateway/login* and missing on a *route group* of the API.

DO NOT skip this because "the app needs login" — that's exactly when this pays off.

---

## The play (5 steps)

### 1. Pull the shell + enumerate the bundles
```bash
curl -s https://console.target.com/ -o index.html
# React/CRA:
grep -oE '/static/js/[^"]+\.js' index.html
# Next.js:
grep -oE '/_next/static/[^"]+\.js' index.html
# generic:
grep -oiE 'src="[^"]+\.js[^"]*"' index.html
```
Download every bundle (they can be multi-MB — that's fine, it's all route data):
```bash
mkdir bundles
for j in $(grep -oE '/static/js/[^"]+\.js' index.html | sort -u); do
  curl -s "https://console.target.com$j" -o "bundles/$(echo "$j"|tr '/' '_')"
done
```

### 2. Harvest API hosts, routes, and secrets from the bundles
```bash
B=bundles/*.js
# Backend API hosts (incl. dev/beta/staging variants — often weaker auth)
grep -ohiE 'https://[a-z0-9.-]*(api|console|backend|service)[a-z0-9.-]*\.target\.com[a-z0-9/_-]*' $B | sort -u
# Versioned API base paths
grep -ohiE '/api/v[0-9]+/?' $B | sort -u
# Route literals — minified bundles store routes as STRING segments, not full URLs.
# Grep for quoted "resource/action" strings:
grep -ohiE '"[a-z0-9_-]+/[a-z0-9_/-]+"' $B | tr -d '"' \
  | grep -iE '(login|user|account|order|billing|invoice|payment|deal|report|token|otp|password|reset|admin|profile|auth|upload|export|role|permission|dashboard|wallet|finance|sales)' | sort -u
# Secrets (validate before trusting — most AIza keys are Maps/analytics, not Auth)
grep -ohiE '(AIza[0-9A-Za-z_-]{35}|AKIA[0-9A-Z]{16}|sk_live_[0-9A-Za-z]+|eyJ[A-Za-z0-9_-]{10,}\.[A-Za-z0-9_-]{10,}|apiKey["'"'"']?\s*[:=]\s*["'"'"'][^"'"'"']+)' $B | sort -u
```
**Note:** minifiers store routes as concatenated string segments (e.g. `"account/payment/list"`), NOT full `/api/v2/...` URLs — so a naive `/api/v*` grep returns nothing. Grep for the **resource-word route strings** and prepend the base yourself.

**Lazy-loaded (async) chunks — don't stop at HTML-referenced bundles.** CRA/webpack SPAs reference only runtime+main+vendor in index.html; numbered async route chunks are named inside main.js's chunk map and loaded at runtime, so grepping only `/static/js/*.js` from the shell truncates route coverage to eager chunks.
```bash
grep -oE '[0-9]+:"[a-f0-9]+"' bundles/*main*.js        # {chunkId:"hash"} pairs
# reconstruct /static/js/<id>.<hash>.chunk.js, download each, re-run route/host/secret harvest
# asset-manifest.json (if present) lists them all -> hunt-source-leak
```

### 3. Establish a CONTROL — find an endpoint that IS gated
Before declaring anything vulnerable, send an unauthenticated request to an endpoint you expect to be protected, and capture what *correct* rejection looks like:
```bash
curl -s -X POST https://api.target.com/api/users -H 'Content-Type: application/json' -d '{}'
# secure → {"error":"Missing or invalid authorization header"} or HTTP 401
```
This is your differential. A sibling API (e.g. a second API host, or a different route group on the same host) is the ideal control — same stack, so a different response = real authz gap, not a quirk.

### 4. Test each route family UNAUTHENTICATED, both methods
For every discovered route, send it with **no `Authorization` header** and compare to the control:
```bash
for r in <routes>; do
  curl -s -o /tmp/r -w "[%{http_code}] $r\n" -X POST -H 'Content-Type: application/json' -d '{}' "https://api.target.com/api/v2/$r"
done
```
Interpret:
- **`401`/`"Missing authorization"`** → gated (correct). Move on.
- **`200` with data** → unauthenticated data exposure. **Finding.**
- **`400 "field X is mandatory"`** → the route processed your request and reached *business-logic validation* without an auth check → **auth bypass; supply the field minimally to confirm.**
- **`200` + verbose DB/stack error** (e.g. `PROCEDURE db_x.sp_y does not exist`) → reached the data layer unauthenticated; also a SQLi-surface signal.
- **Mandatory fields named like `is_admin` / `is_internal` / `requested_by` / `role_id` / `account_type`** → **authorization derived from client-supplied parameters** — set the privilege flag and you self-elevate. Critical-class.

### 5. Pivot & prove (minimally)
- IDs returned by one endpoint (`account_id`, `order_id`, `deal_id`) are the keys the *other* endpoints consume — they prove the whole router is reachable, not just one route.
- Test `dev-`/`beta-`/`staging-` API variants — they frequently have weaker/disabled auth.
- Check the response headers: `Access-Control-Allow-Origin: *` compounds the issue (any web origin reads it from a victim's browser).
- **STOP at minimum-necessary proof.** A handful of records (or a `totalCount`) confirms the missing check. Do NOT enumerate the table — see `redteam-mindset` data-minimization boundary. The finding is the absent auth, not the data volume.

---

## What "the API behind the SSO login" really means

A common, dangerous architecture:
- `console.target.com` (the SPA) → login is **Entra/Okta/Google OAuth** (looks airtight).
- `api.target.com` (the backend) → some route groups enforce the bearer token, **some route groups forgot the middleware.**

The frontend login is theatre if the API doesn't independently validate the token on every route. Always test the API directly, bare, regardless of how locked-down the login UI is.

---

## Anti-patterns

- **"The app requires login, so the API must be protected."** No — test the API directly, unauthenticated. The whole point.
- **"Minified bundle, can't read it."** You don't need to read it — grep it for hosts/routes/secrets. 5 minutes.
- **"`/api/v1/foo` returned 404, so no API here."** Wrong base or wrong method. Try `/api/`, `/api/v2/`, POST not GET, and the exact route strings from the bundle (Express's 404 echoes the path — use it to calibrate).
- **"AIza key found → critical secret."** Validate first — most are Maps/analytics keys (`CONFIGURATION_NOT_FOUND` on identitytoolkit = not Auth-enabled). Don't over-claim.
- **Dumping the whole dataset once you get a 200.** Stop at PoC. (`redteam-mindset`.)
- **Account-creation / write endpoints as "proof".** Read endpoints prove the auth gap without creating state. Never POST a `create`/`signup`/`upload` to "demonstrate" — that's a destructive write needing explicit per-action authorization.

---

## Related Skills & Chains

- **`hunt-api-misconfig`** — once the API is mapped, run the broader misconfig matrix (method tampering, mass assignment, JWT alg confusion) per route.
- **`hunt-idor`** — the `account_id`/`order_id` pivots feed straight into IDOR testing across discovered routes.
- **`hunt-source-leak`** — sourcemaps (`*.js.map`) reconstruct original source for deeper route/secret extraction; same harvesting muscle.
- **`hunt-nextjs`** — for Next.js targets, layer the middleware-bypass (`x-middleware-subrequest`) and `/_next/data` route tests on top of this.
- **`redteam-mindset`** — the data-minimization boundary governs step 5: prove the missing check, don't exfiltrate the table.
- **`recon-scope-triage`** — verify the API host actually belongs to the target before testing (don't pop a same-named third party's API).