Need

Enforce proper control of interaction frequency to prevent abuse and ensure fair resource allocation

Context

• Usage of Ruby 2.7.4 for Ruby programming and development
• Usage of Rails framework for building web applications
• Usage of ActiveRecord for Object-Relational Mapping (ORM) in database operations

Description

Non compliant code

        class PostsController < ApplicationController
  def create
    post = Post.new(post_params)
    if post.save
      render json: post, status: :created
    else
      render json: post.errors, status: :unprocessable_entity
    end
  end

  private

  def post_params
    params.require(:post).permit(:title, :content)
  end
end
        
        

In the above code, we have a PostsController with a create action that is used to create new posts. The create action creates a new Post object with parameters title and content that are passed in the request. If the post is saved successfully, it returns the post as JSON with a status code of 201 (created). If it fails, it returns the errors as JSON with a status code of 422 (unprocessable entity).

The vulnerability in this code is that there is no control over the frequency of interactions. This means that a user can send as many requests to this endpoint as they want in a short period of time. This can lead to a Denial of Service (DoS) attack where the server gets overwhelmed with too many requests and can't process legitimate requests. This can also lead to a user creating a large number of posts in a short period of time, which can be a form of spamming.

Steps

• Implement rate limiting to restrict the number of requests a user can make within a specific time frame.
• Use a middleware or a gem that provides rate limiting functionality.
• Configure the rate limit settings such as the maximum number of requests allowed per user and the time frame for the limit.
• Handle the rate limit exceeded scenario by returning an appropriate response, such as a 429 Too Many Requests status code.
• Consider implementing additional security measures like IP-based rate limiting or using a distributed rate limiting solution for scalability.
• Test the rate limiting functionality to ensure it is working as expected.

Compliant code

        # Add the rack-attack gem to your Gemfile
gem 'rack-attack'

# Then run bundle install
bundle install

# Create a new file config/initializers/rack_attack.rb and add the following code:

class Rack::Attack
  Rack::Attack.cache.store = ActiveSupport::Cache::MemoryStore.new 

  throttle('req/ip', limit: 5, period: 5) do |req|
    req.ip
  end
end

# Update the application.rb file to use the Rack::Attack middleware:

class Application < Rails::Application
  config.middleware.use Rack::Attack
end

# Update the PostsController to handle the rate limit exceeded scenario:

class PostsController < ApplicationController
  def create
    post = Post.new(post_params)
    if post.save
      render json: post, status: :created
    else
      render json: post.errors, status: :unprocessable_entity
    end
  rescue Rack::Attack::Request::Throttled
    render json: { error: 'Rate limit exceeded' }, status: 429
  end

  private

  def post_params
    params.require(:post).permit(:title, :content)
  end
end
        
        

The above code fixes the vulnerability by implementing rate limiting using the rack-attack gem.

First, we add the rack-attack gem to the Gemfile and run bundle install to install it.

Next, we create a new initializer file rack_attack.rb and configure the rate limit settings. In this case, we limit the number of requests to 5 per 5 seconds per IP address.

Then, we update the application.rb file to use the Rack::Attack middleware.

Finally, we update the PostsController to handle the rate limit exceeded scenario. If a user exceeds the rate limit, the server will respond with a 429 Too Many Requests status code and a JSON message indicating that the rate limit has been exceeded.

This solution effectively prevents a user from making too many requests to the server in a short period of time, thus mitigating the risk of a denial-of-service attack.

References

• 108. Improper control of interaction frequency