/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

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):

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

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.

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:

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:

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 en