Broken Access Control in Rails with Api Keys

Broken Access Control occurs when authorization checks are missing, incomplete, or bypassed, allowing attackers to access or modify resources they should not. In Ruby on Rails, using API keys for authentication without enforcing proper authorization per request is a common pattern that can lead to BOLA/IDOR and BFLA vulnerabilities.

Consider a Rails API that authenticates requests via an API key passed in an Authorization header. If the application retrieves the associated user or account but does not ensure that the requested resource (e.g., a document, record, or admin endpoint) belongs to that user or respects tenant boundaries, the access control is broken. For example, an endpoint like GET /api/v1/documents/:id might load a document by ID without verifying that the document’s account_id matches the authenticated API key’s account. An attacker who knows or guesses another document ID can read, update, or delete it entirely due to missing ownership checks.

API keys are long-lived secrets; if they are transmitted over non-TLS channels, stored insecurely, or leaked in logs, they can be reused by attackers to maintain unauthorized access across sessions. Additionally, if the Rails app exposes administrative endpoints (e.g., POST /api/v1/admin/users) and only checks for a role flag without validating the API key’s scope or context, privilege escalation and BFLA become likely. Inadequate rate limiting on key-authenticated endpoints can also enable brute-force enumeration of IDs, compounding the access control issue.

The interplay between authentication via API keys and authorization logic is critical. Without explicit, per-request checks that tie the key to the resource’s ownership or permissions, Rails’ default behaviors (like param filtering or strong parameters) do not prevent unauthorized data access. Compressed into a typical scan of 5–15 seconds, middleBrick tests such unauthenticated attack surfaces and can surface these authorization gaps alongside related findings in categories like Authentication, BOLA/IDOR, and BFLA/Privilege Escalation.

Remediation centers on strict ownership checks and scoping, using API keys to derive the correct context and enforce least privilege. Below are concrete, idiomatic Rails patterns with working code examples.

1. Scoped lookup with API key ownership

Ensure every resource lookup includes the authenticated API key’s scope. Prefer finding through the association rather than by raw ID alone.

# app/controllers/api/v1/documents_controller.rb
class Api::V1::DocumentsController < ApplicationController
  before_action :authenticate_api_key!
  before_action :set_account

  def show
    @document = @account.documents.find(params[:id])
    render json: @document
  end

  private

  def authenticate_api_key!
    api_key = request.headers["Authorization"]&.split(" ")&last
    @api_key = ApiKey.find_by(value: api_key)
    head :unauthorized unless @api_key
  end

  def set_account
    @account = @api_key.account
  end
end

2. Strong parameters and mass assignment protection

Never rely on client-supplied IDs to infer ownership. Use the authenticated key’s context to set foreign keys server-side.

# app/controllers/api/v1/documents_controller.rb (create/update)
def create
  @document = @account.documents.new(document_params)
  if @document.save
    render json: @document, status: :created
  else
    render json: @document.errors, status: :unprocessable_entity
  end
end

def update
  @document = @account.documents.find(params[:id])
  if @document.update(document_params)
    head :no_content
  else
    render json: @document.errors, status: :unprocessable_entity
  end
end

private

def document_params
  params.require(:document).permit(:title, :content)
end

3. Admin endpoints with explicit scope checks

Protect admin routes by verifying the API key has admin privileges within the correct account context.

# app/controllers/api/v1/admin/users_controller.rb
class Api::V1::Admin::UsersController < ApplicationController
  before_action :authenticate_api_key!
  before_action :set_account
  before_action :require_admin!, only: [:index, :create, :destroy]

  def index
    users = @account.users.all
    render json: users
  end

  private

  def require_admin!
    head :forbidden unless @api_key.admin?
  end
end

4. Rate limiting and monitoring

Complement authorization with rate limiting on key-authenticated endpoints to mitigate enumeration and brute-force risks. This example uses Rails cache-based throttling.

# app/controllers/application_controller.rb
class ApplicationController < ActionController::API
  THROTTLE_KEY = lambda { |c| "rate_limit:#{c.request.headers["Authorization"] || c.request.ip}" }

  def throttle(limit: 60, period: 60)
    key = THROTTLE_KEY.call(self)
    current = Rails.cache.read(key) || 0
    if current >= limit
      head :too_many_requests
    else
      Rails.cache.write(key, current + 1, expires_in: period.seconds)
    end
  end
end

Apply throttle as a before_action on sensitive controllers. Combine these practices with transport security (TLS), secure storage of keys, and regular rotation to reduce the likelihood of Broken Access Control when using API keys in Rails.