Need

Secure access control and validation of permissions for accessing sensitive data

Context

• Usage of Python 3.0+ for developing Python applications
• Usage of Django for building web applications in Python

Description

Non compliant code

        from django.shortcuts import get_object_or_404
from django.http import HttpResponse
from .models import Store, Member

def view_store(request, store_id):
    store = get_object_or_404(Store, pk=store_id)
    return HttpResponse(store)

def view_member(request, member_id):
    member = get_object_or_404(Member, pk=member_id)
    return HttpResponse(member)

def add_member(request, store_id, member_id):
    store = get_object_or_404(Store, pk=store_id)
    member = get_object_or_404(Member, pk=member_id)
    store.members.add(member)
    return HttpResponse("Member added")

def modify_member(request, member_id, new_data):
    member = get_object_or_404(Member, pk=member_id)
    member.data = new_data
    member.save()
    return HttpResponse("Member data modified")
        
        

The above code is vulnerable to Insecure Direct Object Reference (IDOR) vulnerability. This is because the application is directly using the user-supplied input ( store_id and member_id) to retrieve objects without checking if the user has the necessary permissions to access or modify those objects.

In the view_store and view_member functions, the application retrieves the Store and Member objects respectively using the IDs provided in the request. If an attacker knows the ID of a store or a member, they can view their information even if they do not have the necessary permissions to do so.

Similarly, in the add_member function, an attacker can add a member to a store just by knowing their IDs. The application does not check if the user has the permission to add members to the store.

In the modify_member function, an attacker can modify the data of a member just by knowing their ID. The application does not check if the user has the permission to modify the member.

This can lead to unauthorized access and modification of data, leading to potential data leaks and other security issues.

Steps

• Implement authentication and authorization checks in your views. This will ensure that only authenticated users can access the views and only authorized users can perform certain actions.
• Use Django's built-in permissions and groups to manage user access. Assign users to specific groups and give these groups permissions to view, add, modify, or delete objects.
• In the view_store and view_member functions, check if the authenticated user has the permission to view the requested store or member.
• In the add_member function, check if the authenticated user has the permission to add members to the requested store.
• In the modify_member function, check if the authenticated user has the permission to modify the requested member.
• If a user tries to perform an action they do not have permission for, return an appropriate HTTP response, such as 403 Forbidden.

Compliant code

        from django.shortcuts import get_object_or_404
from django.http import HttpResponse, HttpResponseForbidden
from .models import Store, Member
from django.contrib.auth.decorators import login_required, permission_required

@login_required
@permission_required('app.view_store', raise_exception=True)
def view_store(request, store_id):
    store = get_object_or_404(Store, pk=store_id)
    return HttpResponse(store)

@login_required
@permission_required('app.view_member', raise_exception=True)
def view_member(request, member_id):
    member = get_object_or_404(Member, pk=member_id)
    return HttpResponse(member)

@login_required
@permission_required('app.add_member', raise_exception=True)
def add_member(request, store_id, member_id):
    store = get_object_or_404(Store, pk=store_id)
    member = get_object_or_404(Member, pk=member_id)
    store.members.add(member)
    return HttpResponse("Member added")

@login_required
@permission_required('app.change_member', raise_exception=True)
def modify_member(request, member_id, new_data):
    member = get_object_or_404(Member, pk=member_id)
    member.data = new_data
    member.save()
    return HttpResponse("Member data modified")
        
        

The updated code now includes Django's built-in decorators for authentication and authorization checks.

- @login_required decorator is used to ensure that only authenticated users can access the views. If a user is not authenticated, they will be redirected to the login page.

- @permission_required decorator is used to check if the authenticated user has the necessary permissions to perform certain actions. The 'raise_exception' parameter is set to True, which means if a user does not have the required permission, a 403 Forbidden response will be returned.

In the view_store and view_member functions, the decorators check if the authenticated user has the permission to view the requested store or member.

In the add_member function, the decorators check if the authenticated user has the permission to add members to the requested store.

In the modify_member function, the decorators check if the authenticated user has the permission to modify the requested member.

This way, the application now validates the necessary permissions to access and modify the data, fixing the insecure object reference vulnerability.

References

• 307. Insecure object reference - Data