Mass Assignment in Grape with Cockroachdb

Mass assignment in a Grape API becomes critical when request parameters are directly bound to database models without explicit allow-listing. With CockroachDB as the backend, the schema and strong consistency characteristics do not prevent over-posting; they only mean that any illicit write reaches a distributed SQL layer that will persist it. An attacker can exploit missing parameter filtering to set fields such as role, admin, or is_confirmed that the client should never control.

Grape does not enforce parameter whitelisting by default. If an endpoint accepts JSON like {"email": "user@example.com", "role": "admin"} and maps params directly to an ActiveRecord (or Sequel) model persisted to CockroachDB, the role field may be set unintentionally. Because CockroachDB supports the full PostgreSQL wire protocol and data types, there are no syntactic differences that would block unwanted assignments; the risk is purely in application-level parameter handling.

Common patterns that expose the vulnerability include using Model.new(params) or model.update(params) where params include non-whitelisted keys. In a distributed SQL setup like CockroachDB, writes succeed quickly, so the lack of input validation results in immediate persistence of unauthorized changes. This maps to the BFLA (Broken Function Level Authorization) and IDOR classes of findings that middleBrick tests, and it may map to OWASP API Top 10 A01:2023 (Broken Object Level Authorization) and compliance frameworks such as SOC2 and GDPR.

Consider a user registration endpoint that also accepts an admin flag. Without explicit permitting, an attacker can craft a request that sets admin: true. Cockroachdb will store this value, and subsequent authorization checks that rely on role attributes may incorrectly grant elevated privileges. middleBrick’s BFLA/IDOR checks are designed to detect such unauthenticated over-privileged write paths before they are exploited in production.

Remediation centers on strict parameter whitelisting before any interaction with CockroachDB. Use a dedicated representer or strong parameters method to permit only safe fields. Never forward the raw params hash directly to model constructors or update calls.

Example of a vulnerable Grape endpoint:

class UserResource < Grape::API
  resource :users do
    post do
      # Dangerous: allows any key to be set
      user = User.new(params[:user])
      if user.save
        { id: user.id }.to_json
      else
        { errors: user.errors.full_messages }.to_json
      end
    end
  end
end

Fixed version using Rails-style strong parameters (or an explicit hash filter):

class UserResource < Grape::API
  helpers do
    def user_params
      # Explicitly permit only safe attributes
      declared(params[:user], include_missing: false).each_with_object({}) do |(k, v), memo|
        memo[k] = v if %w[email first_name last_name].include?(k)
      end
    end
  end

  resource :users do
    post do
      permitted = user_params
      user = User.new(permitted.merge(created_at: Time.now, updated_at: Time.now))
      if user.save
        { id: user.id }.to_json
      else
        error!({ errors: user.errors.full_messages }, 422)
      end
    end
  end
end

When using Sequel with CockroachDB, the approach is analogous—filter before binding:

# db.rb
DB = Sequel.connect(ENV.fetch('COCKROACH_URL'))

# models/user.rb
class User < Sequel::Model
  plugin :validation_helpers
  def validate
    super
    validates_presence [:email]
  end
end

# api/user_api.rb
class UserResource < Grape::API
  resource :users do
    post do
      # Only allow known-safe columns
      allowed = %w[email first_name last_name]
      attrs = declared(params[:user], include_missing: false).slice(*allowed)
      user = User.create(attrs.merge(created_at: Time.now, updated_at: Time.now))
      { id: user.id }.to_json
    rescue Sequel::ValidationFailed => e
      error!({ errors: e.message }, 422)
    end
  end
end

For updates, prefer a method that explicitly selects updatable fields and avoids passing id or timestamps from client input:

helpers do
  def safe_update_params
    declared(params[:user], include_missing: false).each_with_object({}) do |(k, v), memo|
      memo[k] = v if %w[email first_name last_name].include?(k)
    end
  end
end

resource :users do
  put ':id' do
    user = User[params[:id]] or error!('Not found', 404)
    if user.update(safe_update_params.merge(updated_at: Time.now))
      { id: user.id }.to_json
    else
      error!({ errors: user.errors.full_messages }, 422)
    end
  end
end

These patterns ensure that even when CockroachDB receives the write, it contains only intended, validated data. middleBrick’s Property Authorization checks can confirm that no unauthorized fields are accepted by the API surface.