Fix NoSQL Injection in Tornado
NoSQL Injection in Tornado environments typically occurs when raw user input from 'self.get_argument' or JSON request bodies is passed directly into Motor or PyMongo query filters. Without strict type enforcement, attackers can inject operator dictionaries like {'$ne': null} to bypass authentication logic or exfiltrate data.
The Vulnerable Pattern
class AuthHandler(tornado.web.RequestHandler):
async def post(self):
# VULNERABLE: Direct injection of JSON body into query
# Attacker sends: {"user": "admin", "password": {"$ne": "invalid"}}
data = tornado.escape.json_decode(self.request.body)
user = await self.settings['db'].users.find_one({
"username": data.get('user'),
"password": data.get('password')
})
if user:
self.write("Authenticated")The Secure Implementation
The exploit leverages MongoDB's query syntax where a field can accept either a scalar or a dictionary operator. By passing a JSON object instead of a string, an attacker changes the query logic. Casting inputs to 'str()' effectively neutralizes this by forcing the database to look for a literal string matching the malicious payload. In production, utilize Pydantic or Marshmallow to enforce strict schema validation for all incoming Tornado request payloads.
class AuthHandler(tornado.web.RequestHandler):
async def post(self):
data = tornado.escape.json_decode(self.request.body)
# SECURE: Explicit type casting to string prevents operator injection
username = str(data.get('user', ''))
password = str(data.get('password', ''))
user = await self.settings['db'].users.find_one({
"username": username,
"password": password
})
if user:
self.write("Authenticated")</code></pre>
Your Tornado API
might be exposed to NoSQL Injection
74% of Tornado apps fail this check. Hackers use automated scanners to find this specific flaw. Check your codebase before they do.
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