prototype-pollution-tester

Prototype Pollution Tester

Test for client-side JavaScript prototype pollution. Inject __proto__ and constructor.prototype payloads into URL query parameters, hash fragments, and JSON request bodies. Confirm pollution by evaluating Object.prototype in the browser DOM. Capture screenshot evidence on confirmed findings.

Workflow

Phase 1: Recon

1. Mount skill files:

   Read plugins/pentest/skills/common-appsec-patterns/SKILL.md
   Read plugins/pentest/skills/pentest/attacks/client-side/prototype-pollution/prototype-pollution-quickstart.md
   Read plugins/pentest/skills/pentest/attacks/client-side/prototype-pollution/payloads/basic.md
   

2. Navigate to the target and snapshot:

   browser_navigate(url="https://TARGET")
   browser_snapshot()
   

3. Inspect loaded JavaScript libraries to identify pollution-vulnerable patterns:

   browser_network_requests()
   

   Look for: lodash, jQuery, Backbone, Ember, Handlebars, jQuery deparam, qs library. These libraries are historically vulnerable to prototype pollution via object merging functions.
4. Check page source for client-side routing using URL parameters or hash fragments:

   browser_evaluate(function="() => window.location.href")
   browser_evaluate(function="() => Object.keys(window).filter(k => k.includes('router') || k.includes('Router'))")
   

5. Identify JSON endpoints that accept arbitrary nested objects (search POST, filter, config):

   cat outputs/ENGAGEMENT/inventory/api-endpoints.json 2>/dev/null | \
     grep -i '"POST"\|"PUT"' | head -30
   

6. Log:

   {"timestamp":"...","agent":"prototype-pollution-tester","action":"recon","target":"https://TARGET","js_libraries":["lodash/4.17.20","jquery/3.5.1"],"hash_routing":false,"json_endpoints":["POST /api/config","POST /api/search"]}
   

Phase 2: Experiment

Test 1 — URL query parameter injection (__proto__):

browser_navigate(url="https://TARGET/?__proto__[testkey]=polluted")
browser_evaluate(function="() => Object.prototype.testkey")

If evaluate returns "polluted" → VULNERABLE via query parameter.