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Lack of data validation - Header x-amzn-RequestId

Need​

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

Context​

  • Usage of Python 3 for building and running Python applications
  • Usage of Django for building web applications

Description​

Non compliant code​

from django.http import HttpResponse
from django.views import View

class AmazonRequestHandler(View):
    def get(self, request, *args, **kwargs):
        amazon_request_id = request.META.get('HTTP_X_AMZN_REQUESTID')
        # ... process the request using the amazon_request_id
        return HttpResponse('Request processed.')

In the code above, we have a Django view that handles GET requests. The view retrieves the x-amzn-RequestId from the headers of the incoming request using request.META.get('HTTP_X_AMZN_REQUESTID').

This code is vulnerable because it does not validate the x-amzn-RequestId header value before using it. An attacker could potentially inject malicious characters or strings into this header, which could lead to various types of attacks such as SQL Injection, Cross-Site Scripting (XSS), or Remote Code Execution (RCE) depending on how the amazon_request_id is used in the processing of the request.

The vulnerability lies in the fact that the application does not control server-side permission to modify certain fields and allows potentially dangerous character strings to be entered in the x-amzn-RequestId Header. This lack of data validation could lead to serious security issues.

Steps​

  • Implement input validation for the 'x-amzn-RequestId' header. This can be done by checking if the header value matches a certain pattern or length.
  • Use a whitelist of allowed characters and reject any input that contains characters not in the whitelist.
  • Consider using a library or framework that provides built-in functions for input validation.
  • Ensure that the validation is done on the server side, not just on the client side.
  • Log any attempts to input invalid data for further analysis and possible action.
  • Regularly update and review the validation rules to ensure they are still effective against new types of attacks.

Compliant code​

import re
from django.http import HttpResponse, HttpResponseBadRequest
from django.views import View

class AmazonRequestHandler(View):
    def get(self, request, *args, **kwargs):
        amazon_request_id = request.META.get('HTTP_X_AMZN_REQUESTID')

        # Validate the amazon_request_id
        if not self.validate_amazon_request_id(amazon_request_id):
            return HttpResponseBadRequest('Invalid x-amzn-RequestId header.')

        # ... process the request using the amazon_request_id
        return HttpResponse('Request processed.')

    @staticmethod
    def validate_amazon_request_id(amazon_request_id):
        # Define a whitelist of allowed characters (alphanumeric and hyphens)
        pattern = re.compile('^[a-zA-Z0-9-]+$')

        # Check if the amazon_request_id matches the pattern
        if not pattern.match(amazon_request_id):
            return False

        # Check if the amazon_request_id is of a reasonable length
        if len(amazon_request_id) > 255:
            return False

        return True

The updated code includes a validation function validate_amazon_request_id that checks the x-amzn-RequestId header for potentially dangerous characters and length.

The function uses a regular expression to define a whitelist of allowed characters, which in this case includes alphanumeric characters and hyphens. Any x-amzn-RequestId header that contains characters not in this whitelist is considered invalid.

The function also checks the length of the x-amzn-RequestId header. If the header is longer than 255 characters, it is considered invalid. This length check is an additional security measure to prevent potential buffer overflow attacks.

If the x-amzn-RequestId header is invalid, the server responds with a 400 Bad Request status code. This prevents the potentially dangerous request from being processed.

This validation is done on the server side, which is important because client-side validation can be easily bypassed by a malicious user.

By implementing this validation, the application is more secure against injection attacks and other types of attacks that rely on sending malicious data in the x-amzn-RequestId header.

References​

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