Pii Leakage in Grape with Basic Auth

Grape is a REST-like API micro-framework for Ruby that lets you define endpoints and parameters with concise DSL. When Basic Auth is used without additional protections, PII leakage can occur in several ways that middleBrick detects as part of its Data Exposure checks.

Basic Auth sends credentials in an Authorization header encoded as Base64 (not encrypted). If the server logs request details—including headers, query parameters, or the payload—usernames and passwords can be written to log files or exposed via log injection. middleBrick flags this as Data Exposure because logs may contain credentials that should never be persisted.

Additionally, if a Grape API returns full resource representations that include PII (such as email, name, or government identifiers) and does not enforce proper authorization on a per-field basis, unauthenticated or low-privilege actors may receive data they should not see. middleBrick’s Property Authorization check compares the runtime response schema against defined authorizations in the OpenAPI spec to detect over-exposure of PII fields.

When Basic Auth is used without transport encryption (or with weak TLS configurations), credentials and PII can be exposed in transit. middleBrick’s Encryption check verifies that endpoints are served over HTTPS and that strong ciphers are negotiated; unencrypted or downgrade-able endpoints are surfaced with remediation guidance.

Finally, if error messages in Grape reveal stack traces or parameter values—including PII—when authentication fails or validation errors occur, attackers can harvest usernames, emails, or other sensitive data. middleBrick’s Input Validation and Data Exposure checks look for information leakage in responses and map findings to OWASP API Top 10 and PCI-DSS requirements.

To reduce PII leakage risk when using Basic Auth in Grape, combine secure credential handling, strict authorization, and careful error management. Below are concrete patterns you can adopt.

1. Use secure authentication helpers and avoid logging sensitive headers

Ensure your Grape API does not log Authorization headers. Configure your logger to filter sensitive fields.

# config/initializers/grape_logger.rb
class SensitiveParameterFilter
  def self.filter(params)
    filtered = params.dup
    filtered[:authorization] = '[FILTERED]' if filtered[:authorization]
    filtered
  end
end

# In your Grape app
class MyAPI < Grape::API
  format :json
  use Rack::CommonLogger, nil # default; ensure your custom logger filters headers

  before do
    # Example of safe header usage without logging credentials
    auth = request.env['HTTP_AUTHORIZATION']
    if auth&.start_with?('Basic ')
      # Decode for validation only; do not store or log the raw header
      begin
        creds = Base64.strict_decode64(auth.split(' ').last)
        username, password = creds.split(':', 2)
        # Validate credentials via secure service, avoiding logging of username/password
        raise Grape::Http::Status.status_code(401) unless valid_credentials?(username, password)
      rescue ArgumentError
        raise Grape::Http::Status.status_code(400)
      end
    else
      raise Grape::Http::Status.status_code(401)
    end
  end
end

2. Enforce HTTPS and strong transport security

Always serve Basic Auth over TLS. In production, force SSL and use strong ciphers.

# config/application.rb or environment-specific config
Rails.application.configure do
  config.force_ssl = true
end

In your Grape API, you can also explicitly require secure endpoints:

class SecureAPI < Grape::API
  before do
    unless request.ssl? # or request.secure? depending on your setup
      raise Grape::Http::Status.status_code(403)
    end
  end
end

3. Apply per-endpoint authorization and avoid over-exposing PII

Define authorizations that limit returned fields. Use representers or selective serialization to ensure PII is only returned when necessary.

class UserResource < Grape::Entity
  expose :id
  expose :name
  expose :email, if: { |object, options| options[:current_user]&.can_view_email?(object) }
end

class MyAPI < Grape::API
  helpers do
    def current_user
      @current_user ||= User.find_by(username: env['warden'].user)
    end
  end

  resource :users do
    desc 'Get current user info', entity: UserResource
    get do
      present UserResource.represent(current_user, current_user: current_user)
    end
  end
end

4. Return safe error messages

Ensure errors do not leak PII or stack traces. Use generic messages and map internal exceptions to safe HTTP statuses.

rescue_from :all do |e|
  # Log the full exception internally without exposing details to the client
  Rails.logger.error(e)
  error!({ error: 'Unauthorized' }, 401)
end

By combining these practices—header filtering, mandatory TLS, precise authorization, and safe error handling—you reduce the risk of PII leakage when using Basic Auth in Grape.