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Lack of data validation - Header x-amzn-RequestId

Need​

Implementation of secure data validation for the x-amzn-RequestId Header

Context​

  • Usage of Ruby 2.0+ for developing Ruby applications
  • Usage of ActionPack for handling web requests and generating responses in a Ruby on Rails application
  • Usage of ActionController for handling actions and routing in a web application

Description​

Non compliant code​

class ApplicationController < ActionController::Base
  before_action :set_request_id

  private

  def set_request_id
    @request_id = request.headers['x-amzn-RequestId']
  end
end

The above code demonstrates the vulnerability in question. It's a Ruby on Rails controller where we are extracting the 'x-amzn-RequestId' from the request headers and assigning it to an instance variable @request_id.

Here, the application does not validate the 'x-amzn-RequestId' header value that it receives from the client. This means that an attacker could potentially send a harmful string in the 'x-amzn-RequestId' header, which could lead to various security issues such as SQL Injection, Cross-Site Scripting (XSS), or Remote Code Execution depending on how the @request_id is used in the application.

The lack of input validation and sanitization is a common security issue. This is particularly dangerous when the input is used in a context that allows for command or query execution.

Steps​

  • Implement server-side validation for the x-amzn-RequestId header
  • Define a whitelist of allowed characters for the x-amzn-RequestId header
  • Validate the x-amzn-RequestId header against the whitelist of allowed characters
  • Reject or sanitize any input that contains potentially dangerous characters
  • Consider using a regular expression or a validation library to perform the validation
  • Ensure that the validation is performed before using the value of the x-amzn-RequestId header

Compliant code​

class ApplicationController < ActionController::Base
  before_action :set_request_id

  private

  def set_request_id
    request_id = request.headers['x-amzn-RequestId']
    if valid_request_id?(request_id)
      @request_id = request_id
    else
      # Handle invalid request_id as per your application's error handling strategy
      # For example, you might want to log an error, raise an exception, or return a 400 response
    end
  end

  def valid_request_id?(request_id)
    # Define a whitelist of allowed characters for the x-amzn-RequestId header
    # This is just an example, adjust the regular expression to match your requirements
    allowed_characters = /\\A[a-zA-Z0-9\\-_]+\\z/
    request_id.match?(allowed_characters)
  end
end

The updated code includes a new method valid_request_id? that validates the x-amzn-RequestId header against a whitelist of allowed characters. The whitelist is defined as a regular expression, which in this example allows alphanumeric characters, hyphens, and underscores. If the x-amzn-RequestId header contains any characters not in the whitelist, the valid_request_id? method will return false, and the set_request_id method will not set the @request_id instance variable.

This validation is performed before the value of the x-amzn-RequestId header is used, preventing potentially dangerous character strings from being entered. If the x-amzn-RequestId header is invalid, the set_request_id method handles it according to your application's error handling strategy. For example, you might want to log an error, raise an exception, or return a 400 response.

This approach ensures that the application controls server-side permission to modify the x-amzn-RequestId header, mitigating the risk of injection attacks.

References​

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