Django/Auth: Can request.user be exploited and point to other user? - django

Question

Let's say i have a form that does something in database and requires user authentication that has been sent by POST, is it possible inside request someone evil to change the user in order to exploit the system?
The following example creates an item in database but requires a logged in user. Can someone send other user's data in request.user?
from django.shortcuts import render, redirect
from django.contrib.auth.decorators import login_required
from items_core.models import Item
from items.forms import CreateItemForm
from django.views.decorators.csrf import csrf_exempt
#csrf_exempt
#login_required
def create(request):
errors = None
if request.method == 'POST':
form = CreateItemForm(request.POST)
if form.is_valid():
try:
Item.objects.get(
name = form.cleaned_data['name'],
user = request.user
)
errors = 'Item already exist. Please provide other name.'
except Item.DoesNotExist:
Item.objects.create(
name = form.cleaned_data['name'],
user = request.user
)
return redirect('items:list')
form = CreateItemForm()
else:
form = CreateItemForm()
template = {
'form':form,
'items':Item.objects.filter(user=request.user),
'request':request,
'errors':errors
}
return render(request, 'items/item_create.html', template)
Thanks!

Answer 1

The request.user object is of type SimpleLazyObject which is added by the auth middleware to the requestobject.
SimpleLazyObject(LazyObject): is used to delay the instantiation of the wrapped class
At the time of requesting the actual logged in user, get_user method gets called.
def get_user(request):
if not hasattr(request, '_cached_user'):
request._cached_user = auth.get_user(request)
return request._cached_user
Here, auth.get_user() would inturn validate this way:
backend_path = request.session[BACKEND_SESSION_KEY]
backend = load_backend(backend_path)
user = backend.get_user(user_id) or AnonymousUser()
Hence if the request.user object is tampered with, this validation would fail as the session data validation would fail

Answer 2

user attribute on request i.e request.useris set by AuthenticationMiddleware. process_request for this middleware internally uses get_user() provided by django auth system which is defined in django.contrib.auth.__init__.py.
This get_user() uses django session and django session internally use cookies. Django session use a cookie with key as sessionid.
So, say a malicious user gets hold of the cookie of a legitimate user and sends this cookie to the server, server will think that the request has come from a legitimate user and will login as the legitimate user. But since the request was sent by the malicious user, he now has access to the resources of the legitimate user.