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Unauthorized access to files

Need​

Prevention of unauthorized access to files and functionalities

Context​

  • Usage of Python 3.0 for writing Python programs
  • Usage of Django for building web applications

Description​

Non compliant code​

from django.http import HttpResponse
from django.shortcuts import render
from django.views.decorators.csrf import csrf_exempt

@csrf_exempt
def update_user_data(request):
    if request.method == 'POST':
        user_data = request.POST['user_data']
        user_id = request.POST['user_id']
        
        # Update user data in Sharepoint
        update_sharepoint_data(user_id, user_data)
        
        return HttpResponse(status=200)
    else:
        return HttpResponse(status=405)

def update_sharepoint_data(user_id, user_data):
    # Assume this function updates user data in Sharepoint
    pass

The above code is an example of a Django view function that handles HTTP POST requests to update user data. The function update_user_data takes a POST request, extracts the user_data and user_id from the request, and then calls the update_sharepoint_data function to update the user data in Sharepoint.

The vulnerability in this code lies in the fact that there is no input validation or sanitization performed on the user_data and user_id before they are used to update the user data in Sharepoint. This means that an attacker could potentially inject malicious characters or code as part of the user_data or user_id, which could lead to unauthorized access to files and functionalities in Sharepoint.

Moreover, the @csrf_exempt decorator is used, which means that this view is not protected against Cross-Site Request Forgery (CSRF) attacks. In a CSRF attack, an attacker could trick a victim into submitting a malicious request, leading to unauthorized actions being performed on their behalf.

In addition, the code does not check if the user is authenticated and authorized to update the user data. This means that any user, even those not logged in, can send a POST request to this endpoint and update user data, leading to unauthorized access and potential data leakage.

Steps​

  • Validate the input data to prevent injection attacks. This can be done by using regular expressions or built-in validation functions.
  • Implement proper error handling to prevent information leakage that could be exploited by an attacker.
  • Use Django's built-in authentication and authorization mechanisms to ensure that only authorized users can update data.
  • Remove the @csrf_exempt decorator to enable CSRF protection. This will prevent attackers from tricking a user into performing actions without their consent.
  • Ensure that the user has the necessary permissions to update the data in Sharepoint. This can be done by checking the user's role or permissions before updating the data.
  • Use parameterized queries or prepared statements when interacting with Sharepoint to prevent SQL injection attacks.

Compliant code​

from django.http import HttpResponse
from django.shortcuts import render
from django.contrib.auth.decorators import login_required
from django.core.exceptions import PermissionDenied
import re

@login_required
def update_user_data(request):
    if request.method == 'POST':
        user_data = request.POST['user_data']
        user_id = request.POST['user_id']
        
        # Validate input data
        if not validate_input(user_data):
            return HttpResponse('Invalid input', status=400)
        
        # Check user permissions
        if not has_permission(request.user, user_id):
            raise PermissionDenied
        
        # Update user data in Sharepoint
        update_sharepoint_data(user_id, user_data)
        
        return HttpResponse(status=200)
    else:
        return HttpResponse(status=405)

def validate_input(user_data):
    # Use regular expressions to validate input
    pattern = re.compile('^[a-zA-Z0-9]*$')
    return pattern.match(user_data)

def has_permission(user, user_id):
    # Check if the user has the necessary permissions
    # This is a placeholder function, replace with actual permission checking logic
    return user.id == user_id

def update_sharepoint_data(user_id, user_data):
    # Assume this function updates user data in Sharepoint using parameterized queries or prepared statements
    pass

The updated code includes several security improvements:

  1. The @login_required decorator is used to ensure that only authenticated users can access the update_user_data view.

  2. Input validation is performed using a regular expression to prevent injection attacks. The validate_input function checks if the user_data only contains alphanumeric characters.

  3. The has_permission function checks if the user has the necessary permissions to update the data. In this placeholder function, it checks if the user is trying to update their own data. Replace this with your actual permission checking logic.

  4. The update_sharepoint_data function is assumed to use parameterized queries or prepared statements when interacting with Sharepoint to prevent SQL injection attacks.

  5. The @csrf_exempt decorator has been removed to enable CSRF protection. This prevents attackers from tricking a user into performing actions without their consent.

  6. Proper error handling is implemented. If the input data is invalid or the user does not have the necessary permissions, an appropriate HTTP response is returned.

References​

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