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Lack of data validation - Out of range

Need​

Implementation of robust data validation to prevent unauthorized access

Context​

  • Usage of Python 3 for writing and executing Python code
  • Usage of Django for building web applications

Description​

Non compliant code​

from django.shortcuts import render
from django.contrib.auth.decorators import login_required

@login_required
def employee_management(request):
    # Employee Management Functionality
    pass

def absolute_path_bypass(request, path):
    return render(request, path)

In the above code, we have a Django backend application with a function called employee_management that is supposed to be accessible only to authenticated users. This function is decorated with @login_required to ensure only authenticated users can access this functionality.

However, there's another function absolute_path_bypass that takes in a request and a path as arguments. This function renders the template at the absolute path specified, without any checks for user authentication or path validation.

This introduces a vulnerability where an authenticated user can bypass the restrictions put in place by the @login_required decorator on the employee_management function. They can do this by using the absolute_path_bypass function with the absolute path to the employee_management functionality.

The lack of data validation, specifically path validation in this case, allows the user to access restricted functionalities by providing out-of-range inputs. This could potentially lead to unauthorized access and manipulation of data.

Steps​

  • Implement a whitelist of allowed paths that can be accessed through the 'absolute_path_bypass' function. This will prevent users from accessing restricted functionalities.
  • Add a permission check in the 'absolute_path_bypass' function to ensure that the user has the necessary permissions to access the requested path.
  • Consider using Django's built-in URL dispatcher instead of allowing users to specify absolute paths. This can help to prevent path traversal attacks.
  • Use Django's built-in 'UserPassesTestMixin' or 'PermissionRequiredMixin' to restrict access to certain views based on user permissions.

Compliant code​

from django.shortcuts import render
from django.contrib.auth.decorators import login_required
from django.contrib.auth.mixins import UserPassesTestMixin
from django.views import View

@login_required
def employee_management(request):
    # Employee Management Functionality
    pass

class AbsolutePathBypassView(UserPassesTestMixin, View):
    raise_exception = True

    def test_func(self):
        return self.request.path in ['/allowed_path1/', '/allowed_path2/']

    def get(self, request, path):
        return render(request, path)

The updated code now includes a whitelist of allowed paths that can be accessed through the 'AbsolutePathBypassView' function. This is done by overriding the 'test_func' method of the 'UserPassesTestMixin' class. If the requested path is not in the whitelist, a 403 Forbidden response is returned.

The 'UserPassesTestMixin' class is a built-in Django mixin that provides a way to restrict access to certain views based on the result of a test. In this case, the test is whether the requested path is in the whitelist.

The 'raise_exception' attribute is set to True so that a 403 Forbidden response is returned instead of redirecting to the login page if the test fails.

The 'AbsolutePathBypassView' function is now a class-based view, which is a common pattern in Django. Class-based views provide a way to define views that can handle different HTTP methods with separate methods instead of conditional branching inside a single function.

This solution prevents users from accessing restricted functionalities by using absolute paths, and it also provides a clear way to manage and update the list of allowed paths.

References​

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