Buffer Overflow in Hanami with Api Keys

A buffer overflow in a Hanami application that handles API keys can occur when user-supplied key values or key-derived data are copied into fixed-size buffers without proper length checks. In Hanami, API keys are often passed as request parameters, headers, or environment variables, and if the application uses low-level string operations or C extensions, an unexpectedly long key may overflow a static buffer. This can corrupt adjacent memory, overwrite return addresses, or alter control flow, leading to arbitrary code execution or denial of service. The presence of API keys does not directly cause overflows, but they become the attack vector when untrusted input is processed insecurely.

The risk is amplified when API keys are logged, echoed in error messages, or used in string formatting functions that do not validate length. For example, a developer might use strcpy or similar C functions to construct an authorization header or to store a key in a fixed-size structure. If an attacker sends a very long API key, the overflow can overwrite saved frame pointers or exception handlers, potentially allowing injection of malicious code. This violates secure coding practices and maps to common weaknesses in the OWASP API Security Top 10, particularly those related to improper input validation and memory safety.

middleBrick scans for such unsafe consumption patterns by correlating OpenAPI specifications with runtime behavior. If your Hanami API exposes endpoints that accept API keys without validating their size or encoding, the scanner can identify risky code paths and configuration issues. While middleBrick does not fix these issues, it provides prioritized findings with severity ratings and remediation guidance to help you address buffer overflow risks before they are exploited.

To remediate buffer overflow risks related to API keys in Hanami, ensure that all key handling uses safe, high-level abstractions and strict length validation. Avoid low-level memory operations and prefer Ruby’s built-in string and encoding methods, which manage memory automatically. Always treat API keys as untrusted input and apply the same validation rules as for any user-supplied data.

Example: Safe API key handling in Hanami

# app/actions/api_keys/validate_action.rb
module ApiKeys
  class ValidateAction < Hanami::Action
    MAX_KEY_LENGTH = 256

    def call(params)
      api_key = params[:api_key]

      # Validate presence
      unless api_key.is_a?(String) && !api_key.empty?
        halt 400, { error: 'API key must be a non-empty string' }.to_json
      end

      # Validate length to mitigate buffer overflow risks
      if api_key.bytesize > MAX_KEY_LENGTH
        halt 400, { error: 'API key exceeds maximum length' }.to_json
      end

      # Validate format (e.g., alphanumeric with optional hyphens)
      unless api_key.match?(\A[a-zA-Z0-9\-]+\z)
        halt 400, { error: 'API key contains invalid characters' }.to_json
      end

      # Proceed with authentication logic
      authentication = AuthenticationRepository.new.find_by_key(api_key)
      if authentication
        Response.new(status: 200, body: { valid: true }.to_json)
      else
        halt 401, { error: 'Invalid API key' }.to_json
      end
    end
  end
end

This example demonstrates input validation tailored to API keys. By enforcing a maximum length and using a strict character pattern, you reduce the risk of overflow and injection. In Hanami, prefer using form objects or validators to encapsulate these checks and keep your actions lean.

Example: Secure configuration with environment variables

# config/initializers/api_keys.rb
module HanamiApp
  module Configuration
    def self.api_key
      key = ENV['HANAMI_API_KEY']
      return nil unless key

      # Ensure the key read from environment is within safe bounds
      if key.bytesize > 512
        raise ArgumentError, 'Environment-provided API key is too long'
      end

      key
    end
  end
end

When API keys are sourced from environment variables, validate their length at boot time to prevent runtime surprises. This approach complements runtime checks and aligns with secure deployment practices. middleBrick’s continuous monitoring in the Pro plan can alert you if API key length validation is missing across your endpoints.

Example: Using middleware for global validation

# lib/middleware/api_key_validator.rb
class ApiKeyValidator
  def initialize(app)
    @app = app
  end

  def call(env)
    request = Rack::Request.new(env)
    api_key = request.get_header('HTTP_X_API_KEY')

    if api_key&.bytesize > 1024
      return [400, { 'Content-Type' => 'application/json' }, [{ error: 'API key too long' }.to_json]]
    end

    @app.call(env)
  end
end

# config/application.rb
use ApiKeyValidator

Middleware can enforce length limits before requests reach your Hanami actions, adding a defensive layer. Combine this with strict parameter validation in your actions for comprehensive protection.