Web Auth Defenses Testing

Web Auth Defenses Testing

Purpose

Test login/account-defense controls the way a bug-bounty reviewer scores them: determine scope of any lockout, find logic anomalies, and confirm (or refute) hosted-app auth weaknesses — without locking real users or sustaining an outage.

When to use

• Target exposes POST /api/auth/{login,register,forgot-password,mfa/verify} or similar.
• You see a "too many attempts" / lockout / rate-limit response during auth testing.
• You're assessing a Next.js/Vercel or other hosted-SPA app with separate auth + backend services.
• Companion to web-pentest (this skill drills the auth-defense sub-area in depth).

Phase 1 — Lockout scope determination (MOST IMPORTANT, drives severity)

A failed-login lockout is keyed one of three ways; impact differs by ~10x:

• per-account → only the targeted victim denied (Medium/High)
• per-IP → only attacker's source throttled (Low)
• GLOBAL/shared→ entire site cannot log in (Critical, CVSS ~9.1, full auth outage)

Probe recipe (run in order, NEVER use real users' emails)

# (a) ~6 bad logins to a RANDOM fresh email:
for i in $(seq 1 6); do
  curl -s -X POST https://TARGET/api/auth/login -H "Content-Type: application/json" \
    -d "{\"email\":\"locktest_$i@randomexample.com\",\"password\":\"wrongpass\"}"
done

# (b) test a DIFFERENT fresh email once:
curl -s -X POST https://TARGET/api/auth/login -H "Content-Type: application/json" \
  -d '{"email":"other_fresh@randomexample.com","password":"wrongpass"}'
#  "N attempts remaining" -> per-EMAIL (per-account)
#  "locked" + SAME resetTime -> GLOBAL

# (c) DEFINITIVE: brand-new email never contacted before:
curl -s -X POST https://TARGET/api/auth/login -H "Content-Type: application/json" \
  -d "{\"email\":\"neverseen_$(date +%s)@fresh.io\",\"password\":\"x\"}"
#  locked w/ identical resetTime as (a) -> GLOBAL shared counter CONFIRMED.

Capture resetTime each time; identical timestamps across unrelated emails prove a shared counter. Compare to date -u for lock-window duration. Always run (c) before scoring.

Phase 2 — Operational safety (do not cause harm)

• Use only random never-seen emails as lock targets. Do NOT probe guessed real addresses (admin@, support@, info@) — you may lock real users and trigger a real global outage.
• Stop sending login requests once the lockout is confirmed. A global lock may not clear within a short window; continued probing sustains the outage. Confirm, then cease.
• If a real-looking address was accidentally locked, note it as impact evidence, then stop.
• Registering a test account to reach authenticated areas may fail while a global lock is active — wait it out or use a fresh source rather than hammering.

Phase 3 — Error-handling & enumeration differentials

• Invalid email format vs valid format vs valid + wrong password often yield different messages (400 "Invalid email" vs 401 "Invalid credentials. N remaining"). Low (enum aid).
• /forgot-password returning 500 for every valid-format input (while 400 for bad format) = broken reset flow / weak error handling (Medium). Record the exact body.

Phase 4 — Auth-route method / logic anomalies

• After OPTIONS on an auth route, read Allow: (e.g. DELETE, OPTIONS, POST). Test surprises:

  curl -s -X DELETE https://TARGET/api/auth/login -H "Content-Type: application/json" -d '{}'
  # 200 {"success":true} without auth = logic anomaly (Medium)
  

• PUT/TRACE should be 405. Method-override headers should be ignored.

Phase 5 — Hosted-app (Next.js/Vercel) auth probing

• httpx -tech-detect → Vercel, HSTS, sometimes C3.js; apex IP is Vercel anycast.
• Protected routes: expect 307 → /login (GET) and /api/dashboard/* → 401 without session. That is access control WORKING — record as confirmed non-issue, not a finding.
• Source maps <chunk>.js.map → usually 403 (safe). Hidden .env/.git/.svn → 403/404.
• CORS Access-Control-Allow-Origin: * is LOW unless Access-Control-Allow-Credentials: true also present.
• Missing X-Frame-Options / CSP frame-ancestors / X-Content-Type-Options / Referrer-Policy → clickjacking Low finding.
• Mass-assignment: send role":"admin" / isAdmin":true in register; verify server echoes role":"user" (rejected) vs honors it.

Phase 6 — Separate backend gateway discovery

• /docs often embeds a real backend URL in sample curl (e.g. https://<svc>.up.railway.app). Probe separately: $B/health (leaks service name/mode/uptime), $B/v1/chat/completions (401 with distinct no-key vs bad-key message). Flag CORS * only if a valid key can reach a browser context; if frontend proxies server-side, it's low-risk. Info/Low.

Phase 7 — Platform variants: Moodle (and classic PHP form-logins)

Moodle logins are form-POST with a MoodleSession cookie, not JSON APIs — adapt Phase 1:

• CSRF token (logintoken) may not block scripts: POSTing /login/index.php with an EMPTY logintoken field was processed normally in the wild (303 → form re-render "Invalid login"). Test once with an empty value; don't assume the token defeats scripted probes.
• Rate-limit probe shape: 8 failed POSTs, fake username (rateprobe_nonexistent), 0.3 s interval → alternating 303/200 with "Invalid login" each time and zero throttle/lockout/captcha keywords = NO rate-limit observed up to N attempts. Report as a bounded lower bound (Medium when accounts are students/staff: credential stuffing path); never claim "unlimited". Stop at the first throttle signal or ~8 attempts, whichever first.
• Parallel surface: /login/token.php (mobile web service, JSON) processes bad credentials too — run the same gap check; it's what mobile-app stuffing actually hits.
• forgot-password is NOT an enum oracle here: valid and invalid usernames both return 200 with generic text; only sesskey/random-token bytes differ between bodies. Hash-diff full bodies and inspect diff fragments before claiming enumeration — status-code equality proves nothing (opposite of the JSON-API differential in Phase 3).

Reporting

• Score lockout by scope: GLOBAL → Critical; per-account → High/Medium; per-IP → Low.
• Always include the resetTime comparison as evidence for a global finding.
• Provide a self-contained poc.py that reproduces with a random email and stops after confirming.

References

• references/lockout_and_hosted_app_testing.md — full probe recipes, curl snippets, and tooling notes for lockout-scope determination, hosted-app specifics, and backend discovery.