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Lack of data validation - Dates

Need​

Implementation of robust data validation for date fields

Context​

  • Usage of Python 3 for scripting and application development
  • Usage of Django for building web applications in Python

Description​

Non compliant code​

from django.http import JsonResponse
from django.views import View
from myapp.models import Event

class EventView(View):
    def post(self, request, *args, **kwargs):
        event_id = request.POST.get('event_id')
        new_date = request.POST.get('new_date')

        event = Event.objects.get(id=event_id)
        event.date = new_date
        event.save()

        return JsonResponse({'status': 'success'})

In the above code, the EventView class has a post method that accepts a request, extracts an event_id and a new_date from the request, and then updates the date of the event with the provided event_id.

The vulnerability here is that there is no server-side validation to check if the new_date is actually a valid date format. It simply takes any value from the new_date field and saves it to the date field of the event.

Moreover, there is no check to see if the user has the necessary permissions to modify the event date. The server blindly processes any request to modify the event date.

This means that an attacker could potentially send a malformed or malicious new_date value, or update the date of an event they do not have permission to modify. As the server does not perform any validation, it would accept and process this as a valid request, leading to potential data integrity issues.

Steps​

  • Validate the 'new_date' input on the server side to ensure it is in the correct date format before saving it to the database.
  • Implement user permissions check on the server side to ensure the user has the right to modify the event date.
  • Consider using Django's form or model form for better validation of input data.
  • Handle the case when the 'event_id' does not exist in the database to prevent server errors.
  • Ensure that the 'new_date' is not in the past or a date that could disrupt the logic of the application.

Compliant code​

from django.http import JsonResponse
from django.views import View
from django.core.exceptions import ObjectDoesNotExist
from django import forms
from myapp.models import Event
import datetime

class EventForm(forms.ModelForm):
    class Meta:
        model = Event
        fields = ['date']

class EventView(View):
    def post(self, request, *args, **kwargs):
        event_id = request.POST.get('event_id')
        new_date = request.POST.get('new_date')

        # Check if the event exists
        try:
            event = Event.objects.get(id=event_id)
        except ObjectDoesNotExist:
            return JsonResponse({'status': 'failure', 'error': 'Event does not exist'})

        # Check if the user has permission to modify the event
        if not request.user.has_perm('change_event', event):
            return JsonResponse({'status': 'failure', 'error': 'No permission to modify event'})

        # Validate the new date
        form = EventForm(request.POST)
        if form.is_valid():
            # Check if the new date is not in the past
            if datetime.datetime.strptime(new_date, '%Y-%m-%d') < datetime.datetime.now():
                return JsonResponse({'status': 'failure', 'error': 'Date is in the past'})
            event.date = form.cleaned_data['date']
            event.save()
            return JsonResponse({'status': 'success'})
        else:
            return JsonResponse({'status': 'failure', 'error': 'Invalid date format'})

The updated code now includes several checks to ensure data integrity and security:

  1. Existence of Event: The code checks if the event with the provided event_id exists in the database. If not, it returns a failure status with an appropriate error message.

  2. User Permissions: The code checks if the user making the request has the necessary permissions to modify the event. This is done using Django's built-in has_perm function.

  3. Date Validation: The code uses Django's ModelForm for validating the new_date input. If the input is not in the correct date format, the form will be invalid and a failure status with an appropriate error message is returned.

  4. Date Logic: The code checks if the new_date is in the past. If it is, a failure status with an appropriate error message is returned. This prevents users from setting event dates that could disrupt the logic of the application.

By implementing these checks, the server-side validation is significantly improved, making the application more secure and robust.

References​

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