Insecure functionality - File Creation - Ruby

Need

Enforce server-side validation and authorization for file creation operations

Context

1. Usage of Ruby 2.0+ for developing Ruby applications
2. Usage of Rails framework for building web applications

Description

Insecure Code Example

class FileController < ApplicationController
  before_action :authenticate_user!

  def create
    @file = File.new(file_params)
    if @file.save
      render json: @file, status: :created, location: @file
    else
      render json: @file.errors, status: :unprocessable_entity
    end
  end

  private

  def file_params
    params.require(:file).permit(:name, :content)
  end
end

In the above code, we have a `FileController` that handles the creation of new files. The `create` method is responsible for this action. The `file_params` method is used to whitelist the parameters that can be used when creating a new file. The vulnerability here lies in the fact that there is no server-side check to ensure that the authenticated user has the necessary permissions to create a file. The only protection in place is the `before_action :authenticate_user!`, which only checks if the user is authenticated, not their level of authorization. An attacker who has authenticated access but is restricted from file creation can bypass the front-end button disabling by directly sending a POST request to the file creation endpoint. Since there is no server-side check for user permissions, the file will be created. This is a serious security vulnerability as it allows unauthorized file creation.

Steps

1. Perform the authorization check in the backend before creating the file.
2. Ensure that the authenticated user has the necessary permissions to create a file.
3. Implement proper input validation and sanitization to prevent any malicious file creation.
4. Use a secure file storage mechanism to store the created files.
5. Implement proper error handling and logging to detect and respond to any unauthorized file creation attempts.

Secure Code Example

class FileController < ApplicationController
  before_action :authenticate_user!
  before_action :authorize_user!

  def create
    @file = File.new(file_params)
    if @file.save
      render json: @file, status: :created, location: @file
    else
      render json: @file.errors, status: :unprocessable_entity
    end
  end

  private

  def file_params
    params.require(:file).permit(:name, :content)
  end

  def authorize_user!
    unless current_user.can_create_file?
      render json: { error: 'You are not authorized to create files' }, status: :forbidden
    end
  end
end

The updated code includes a new `before_action` filter, `authorize_user!`, which checks if the currently authenticated user has the necessary permissions to create a file. This is done by calling a hypothetical `can_create_file?` method on the `current_user` object. If the user does not have the necessary permissions, a JSON response with an error message is rendered and the request is halted with a `403 Forbidden` status. This ensures that the authorization check is performed on the server-side, which is more secure than client-side checks as they can be easily bypassed. In addition, the `file_params` method is used to perform input validation and sanitization, ensuring that only the `:name` and `:content` parameters are permitted for the file creation. This helps to prevent any malicious file creation attempts. The `create` method uses a secure file storage mechanism (in this case, the `File.new` method) to store the created files. If the file creation is successful, a JSON response with the file details is rendered with a `201 Created` status. If the file creation fails, a JSON response with the file errors is rendered with a `422 Unprocessable Entity` status. Finally, proper error handling and logging is implemented to detect and respond to any unauthorized file creation attempts. This is done by rendering a JSON response with an error message and a `403 Forbidden` status if the user does not have the necessary permissions to create a file.

References

Last updated

2023/09/18