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Lack of data validation - Input Length

Need​

Enforce input length validation to prevent excessive data submission and potential security vulnerabilities.

Context​

  • Requirement of Ruby 2.0 or higher for running the application
  • Usage of Rails framework for building web applications

Description​

Non compliant code​

class UsersController < ApplicationController
  def create
    @user = User.new(params[:user])
    if @user.save
      redirect_to @user
    else
      render 'new'
    end
  end
end

The above code is a simple create action in a UsersController in a Ruby on Rails application. The vulnerability lies in the line @user = User.new(params[:user]).

This line creates a new user with the parameters sent in the request, without any validation on the length of the input data. An attacker could potentially send a very large amount of data in the user parameter, which could lead to various issues such as Denial of Service (DoS), Buffer Overflow attacks, or exhausting system resources.

The lack of input length validation increases the attack surface and makes the application vulnerable to attacks. It's important to always validate the length of the input data to prevent such vulnerabilities.

Steps​

  • Implement input length validation on the user creation endpoint.
  • Determine the maximum allowed length for each input field.
  • Validate the length of each input field before saving the user.
  • Return an appropriate error message if the input length exceeds the maximum allowed length.
  • Consider implementing client-side validation to provide immediate feedback to the user.

Compliant code​

class UsersController < ApplicationController
  def create
    @user = User.new(user_params)
    if @user.valid?
      if @user.save
        redirect_to @user
      else
        render 'new'
      end
    else
      render json: { error: "Input length exceeds the maximum allowed length" }, status: 400
    end
  end

  private

  def user_params
    params.require(:user).permit(:username, :email, :password).tap do |user_params|
      user_params.each do |key, value|
        if value.length > MAX_LENGTH
          user_params.delete(key)
        end
      end
    end
  end
end

The updated code includes a private method user_params that sanitizes the user input. This method uses the permit method to only allow specific parameters to be passed in. It then iterates over each of these parameters and checks their length. If the length of any parameter exceeds the maximum allowed length (MAX_LENGTH), it is removed from the parameters.

In the create method, before saving the user, we call @user.valid? to check if the user is valid. This method will return false if any of the validations defined in the User model fail, including the length validation.

If the user is not valid, we render a JSON response with an appropriate error message and a 400 status code. This provides immediate feedback to the client about the error.

This approach ensures that only valid data is saved to the database, and provides clear feedback to the client when invalid data is submitted. It also helps to prevent potential security issues related to excessively long input values.

References​

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