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HTTP parameter pollution

Need​

Prevention of HTTP parameter pollution

Context​

  • Usage of Python 3 for developing applications and scripts
  • Usage of Django for building web applications in Python

Description​

Non compliant code​

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

class MyView(View):
    def get(self, request, *args, **kwargs):
        user_id = request.GET.get('user_id')
        #... some code that uses user_id

        return HttpResponse('Hello, World!')

In the above code, we have a Django view that accepts GET requests. The get method retrieves the user_id parameter from the GET request using the request.GET.get('user_id').

The vulnerability here is that the application does not validate or sanitize the user_id parameter before using it. This means an attacker can inject extra parameters into the HTTP request, causing unexpected behavior on the server. This is known as HTTP parameter pollution.

For example, an attacker could send a request like GET /myview?user_id=1&user_id=2. The Django application would only use the last user_id parameter in the request (i.e., user_id=2), causing unexpected behavior if the application logic depends on the user_id value.

Moreover, if the user_id parameter is used in a database query, this could potentially lead to more serious vulnerabilities like SQL Injection, if the database engine interprets the extra parameters as SQL commands.

Steps​

  • Validate the input parameters to ensure they meet the expected format and type.
  • Limit the number of parameters that can be passed to the server to prevent pollution.
  • Implement a strong server-side input validation and sanitization mechanism.
  • Use a web application firewall (WAF) to filter out malicious requests.
  • Regularly update and patch your server software to protect against known vulnerabilities.

Compliant code​

from django.http import HttpResponse
from django.views import View
from django.core.exceptions import ValidationError

class MyView(View):
    def get(self, request, *args, **kwargs):
        user_id = request.GET.get('user_id')

        # Validate the user_id
        if not self.validate_user_id(user_id):
            raise ValidationError('Invalid user_id')

        #... some code that uses user_id

        return HttpResponse('Hello, World!')

    @staticmethod
    def validate_user_id(user_id):
        # Check if user_id is not None and is a digit
        return user_id is not None and user_id.isdigit()

The updated code includes a validation function validate_user_id that checks if the user_id is not None and if it is a digit. This ensures that only valid user_id values are processed. If an invalid user_id is encountered, a ValidationError is raised.

This approach helps to prevent HTTP parameter pollution by ensuring that only valid parameters are processed. It's important to note that this is a basic validation and depending on the complexity of your application, you might need a more robust validation mechanism.

In addition to this, it's recommended to limit the number of parameters that can be passed to the server to prevent pollution, implement a strong server-side input validation and sanitization mechanism, use a web application firewall (WAF) to filter out malicious requests, and regularly update and patch your server software to protect against known vulnerabilities.

References​

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