Lack of data validation - Headers - Ruby

Need

Implementation of proper data validation for HTTP headers

Context

1. Usage of Ruby 2.5.0 for Ruby programming and development
2. Usage of Ruby for building dynamic and object-oriented applications
3. Usage of Rails framework for building web applications

Description

Insecure Code Example

class ApplicationController < ActionController::Base
  def show
    @user = User.find(params[:id])
    response.headers["X-Username"] = @user.username
  end
end

In the above code snippet, the `show` method in the `ApplicationController` is retrieving a user's information based on the `id` parameter passed in the request. It then sets the `X-Username` header to the username of the found user. The vulnerability lies in the fact that there is no validation being performed on the `@user.username` before it's being set in the header. This lack of validation means that an attacker could potentially manipulate the username to include malicious scripts or commands, leading to a Cross-Site Scripting (XSS) attack or other security breaches. For instance, if the `username` field in the database is not properly sanitized and allows for special characters, an attacker could inject scripts or commands like `"><script>malicious_code_here</script>` or `"; rm -rf /*`. When this `username` is used and set in the `X-Username` header, the injected code could be executed leading to potential security risks.

Steps

1. Implement input validation for the 'X-Username' header to ensure it only contains safe characters.
2. Use appropriate encoding or escaping techniques to prevent any potential injection attacks.
3. Consider using a whitelist approach to validate the 'X-Username' header value against a predefined set of allowed characters or patterns.
4. Sanitize the 'X-Username' header value before using it to prevent any potential XSS attacks.
5. Regularly update and patch the Ruby on Rails framework to benefit from the latest security enhancements and fixes.

Secure Code Example

class ApplicationController < ActionController::Base
  def show
    @user = User.find(params[:id])
    username = sanitize(@user.username)
    response.headers["X-Username"] = username if valid_username?(username)
  end

  private

  def sanitize(input)
    ActionController::Base.helpers.sanitize(input)
  end

  def valid_username?(username)
    # Define a regex for a valid username
    valid_username_regex = /\\A[a-zA-Z0-9_]*\\z/
    username.match?(valid_username_regex)
  end
end

The updated code includes two new methods: `sanitize` and `valid_username?`. The `sanitize` method uses the `sanitize` helper method provided by the `ActionController::Base.helpers` module to sanitize the username. This method strips out all HTML tags and attributes, ensuring that no malicious scripts can be injected via the username. The `valid_username?` method checks if the username matches a predefined regular expression (`valid_username_regex`). This regular expression only allows alphanumeric characters and underscores, which are typically safe and commonly used in usernames. This is a whitelist approach to input validation, which is generally more secure than a blacklist approach. In the `show` method, the username is first sanitized and then validated. The `X-Username` header is only set if the username is valid. This ensures that only safe, valid usernames are included in the HTTP headers, preventing potential XSS attacks and preserving the integrity of the stored information. Remember to regularly update and patch the Ruby on Rails framework to benefit from the latest security enhancements and fixes.

References

Last updated

2023/09/18