Prevented data leakage in contrib.admin via query string manipulation.

This is a security fix. Disclosure following shortly.

django/contrib/admin/exceptions.py

@@ -4,3 +4,8 @@ from django.core.exceptions import SuspiciousOperation
 class DisallowedModelAdminLookup(SuspiciousOperation):
     """Invalid filter was passed to admin view via URL querystring"""
     pass
+
+
+class DisallowedModelAdminToField(SuspiciousOperation):
+    """Invalid to_field was passed to admin view via URL query string"""
+    pass

django/contrib/admin/options.py

@@ -11,6 +11,7 @@ from django.contrib.admin import widgets, helpers
 from django.contrib.admin import validation
 from django.contrib.admin.checks import (BaseModelAdminChecks, ModelAdminChecks,
     InlineModelAdminChecks)
+from django.contrib.admin.exceptions import DisallowedModelAdminToField
 from django.contrib.admin.utils import (quote, unquote, flatten_fieldsets,
     get_deleted_objects, model_format_dict, NestedObjects,
     lookup_needs_distinct)
@@ -434,6 +435,24 @@ class BaseModelAdmin(six.with_metaclass(forms.MediaDefiningClass)):
                 valid_lookups.append(filter_item)
         return clean_lookup in valid_lookups
 
+    def to_field_allowed(self, request, to_field):
+        opts = self.model._meta
+
+        try:
+            field = opts.get_field(to_field)
+        except FieldDoesNotExist:
+            return False
+
+        # Make sure at least one of the models registered for this site
+        # references this field.
+        registered_models = self.admin_site._registry
+        for related_object in opts.get_all_related_objects():
+            if (related_object.model in registered_models and
+                    field in related_object.field.foreign_related_fields):
+                return True
+
+        return False
+
     def has_add_permission(self, request):
         """
         Returns True if the given request has permission to add an object.
@@ -1337,6 +1356,10 @@ class ModelAdmin(BaseModelAdmin):
     @transaction.atomic
     def changeform_view(self, request, object_id=None, form_url='', extra_context=None):
 
+        to_field = request.POST.get(TO_FIELD_VAR, request.GET.get(TO_FIELD_VAR))
+        if to_field and not self.to_field_allowed(request, to_field):
+            raise DisallowedModelAdminToField("The field %s cannot be referenced." % to_field)
+
         model = self.model
         opts = model._meta
         add = object_id is None
@@ -1409,8 +1432,7 @@ class ModelAdmin(BaseModelAdmin):
             original=obj,
             is_popup=(IS_POPUP_VAR in request.POST or
                       IS_POPUP_VAR in request.GET),
-            to_field=request.POST.get(TO_FIELD_VAR,
+            to_field=to_field,
-                                      request.GET.get(TO_FIELD_VAR)),
             media=media,
             inline_admin_formsets=inline_formsets,
             errors=helpers.AdminErrorList(form, formsets),

django/contrib/admin/views/main.py

@@ -12,7 +12,9 @@ from django.utils.translation import ugettext, ugettext_lazy
 from django.utils.http import urlencode
 
 from django.contrib.admin import FieldListFilter
-from django.contrib.admin.exceptions import DisallowedModelAdminLookup
+from django.contrib.admin.exceptions import (
+    DisallowedModelAdminLookup, DisallowedModelAdminToField,
+)
 from django.contrib.admin.options import IncorrectLookupParameters, IS_POPUP_VAR, TO_FIELD_VAR
 from django.contrib.admin.utils import (quote, get_fields_from_path,
     lookup_needs_distinct, prepare_lookup_value)
@@ -58,7 +60,10 @@ class ChangeList(object):
             self.page_num = 0
         self.show_all = ALL_VAR in request.GET
         self.is_popup = IS_POPUP_VAR in request.GET
-        self.to_field = request.GET.get(TO_FIELD_VAR)
+        to_field = request.GET.get(TO_FIELD_VAR)
+        if to_field and not model_admin.to_field_allowed(request, to_field):
+            raise DisallowedModelAdminToField("The field %s cannot be referenced." % to_field)
+        self.to_field = to_field
         self.params = dict(request.GET.items())
         if PAGE_VAR in self.params:
             del self.params[PAGE_VAR]

docs/ref/exceptions.txt

@@ -56,6 +56,7 @@ SuspiciousOperation
 
     * DisallowedHost
     * DisallowedModelAdminLookup
+    * DisallowedModelAdminToField
     * DisallowedRedirect
     * InvalidSessionKey
     * SuspiciousFileOperation

docs/releases/1.4.14.txt

@@ -47,3 +47,18 @@ and the ``RemoteUserBackend``, a change to the ``REMOTE_USER`` header between
 requests without an intervening logout could result in the prior user's session
 being co-opted by the subsequent user. The middleware now logs the user out on
 a failed login attempt.
+
+Data leakage via query string manipulation in ``contrib.admin``
+===============================================================
+
+In older versions of Django it was possible to reveal any field's data by
+modifying the "popup" and "to_field" parameters of the query string on an admin
+change form page. For example, requesting a URL like
+``/admin/auth/user/?pop=1&t=password`` and viewing the page's HTML allowed
+viewing the password hash of each user. While the admin requires users to have
+permissions to view the change form pages in the first place, this could leak
+data if you rely on users having access to view only certain fields on a model.
+
+To address the issue, an exception will now be raised if a ``to_field`` value
+that isn't a related field to a model that has been registered with the admin
+is specified.

docs/releases/1.5.9.txt

@@ -47,3 +47,18 @@ and the ``RemoteUserBackend``, a change to the ``REMOTE_USER`` header between
 requests without an intervening logout could result in the prior user's session
 being co-opted by the subsequent user. The middleware now logs the user out on
 a failed login attempt.
+
+Data leakage via query string manipulation in ``contrib.admin``
+===============================================================
+
+In older versions of Django it was possible to reveal any field's data by
+modifying the "popup" and "to_field" parameters of the query string on an admin
+change form page. For example, requesting a URL like
+``/admin/auth/user/?pop=1&t=password`` and viewing the page's HTML allowed
+viewing the password hash of each user. While the admin requires users to have
+permissions to view the change form pages in the first place, this could leak
+data if you rely on users having access to view only certain fields on a model.
+
+To address the issue, an exception will now be raised if a ``to_field`` value
+that isn't a related field to a model that has been registered with the admin
+is specified.

docs/releases/1.6.6.txt

@@ -48,6 +48,21 @@ requests without an intervening logout could result in the prior user's session
 being co-opted by the subsequent user. The middleware now logs the user out on
 a failed login attempt.
 
+Data leakage via query string manipulation in ``contrib.admin``
+===============================================================
+
+In older versions of Django it was possible to reveal any field's data by
+modifying the "popup" and "to_field" parameters of the query string on an admin
+change form page. For example, requesting a URL like
+``/admin/auth/user/?_popup=1&t=password`` and viewing the page's HTML allowed
+viewing the password hash of each user. While the admin requires users to have
+permissions to view the change form pages in the first place, this could leak
+data if you rely on users having access to view only certain fields on a model.
+
+To address the issue, an exception will now be raised if a ``to_field`` value
+that isn't a related field to a model that has been registered with the admin
+is specified.
+
 Bugfixes
 ========
 

tests/admin_views/tests.py

@@ -18,6 +18,7 @@ from django.contrib.auth import get_permission_codename
 from django.contrib.admin import ModelAdmin
 from django.contrib.admin.helpers import ACTION_CHECKBOX_NAME
 from django.contrib.admin.models import LogEntry, DELETION
+from django.contrib.admin.options import TO_FIELD_VAR
 from django.contrib.admin.templatetags.admin_static import static
 from django.contrib.admin.templatetags.admin_urls import add_preserved_filters
 from django.contrib.admin.tests import AdminSeleniumWebDriverTestCase
@@ -598,6 +599,36 @@ class AdminViewBasicTest(AdminViewBasicTestCase):
         response = self.client.get("/test_admin/admin/admin_views/workhour/?employee__person_ptr__exact=%d" % e1.pk)
         self.assertEqual(response.status_code, 200)
 
+    def test_disallowed_to_field(self):
+        with patch_logger('django.security.DisallowedModelAdminToField', 'error') as calls:
+            response = self.client.get("/test_admin/admin/admin_views/section/", {TO_FIELD_VAR: 'missing_field'})
+            self.assertEqual(response.status_code, 400)
+            self.assertEqual(len(calls), 1)
+
+        # Specifying a field that is not refered by any other model registered
+        # to this admin site should raise an exception.
+        with patch_logger('django.security.DisallowedModelAdminToField', 'error') as calls:
+            response = self.client.get("/test_admin/admin/admin_views/section/", {TO_FIELD_VAR: 'name'})
+            self.assertEqual(response.status_code, 400)
+            self.assertEqual(len(calls), 1)
+
+        # Specifying a field referenced by another model should be allowed.
+        response = self.client.get("/test_admin/admin/admin_views/section/", {TO_FIELD_VAR: 'id'})
+        self.assertEqual(response.status_code, 200)
+
+        # We also want to prevent the add and change view from leaking a
+        # disallowed field value.
+        with patch_logger('django.security.DisallowedModelAdminToField', 'error') as calls:
+            response = self.client.post("/test_admin/admin/admin_views/section/add/", {TO_FIELD_VAR: 'name'})
+            self.assertEqual(response.status_code, 400)
+            self.assertEqual(len(calls), 1)
+
+        section = Section.objects.create()
+        with patch_logger('django.security.DisallowedModelAdminToField', 'error') as calls:
+            response = self.client.post("/test_admin/admin/admin_views/section/%d/" % section.pk, {TO_FIELD_VAR: 'name'})
+            self.assertEqual(response.status_code, 400)
+            self.assertEqual(len(calls), 1)
+
     def test_allowed_filtering_15103(self):
         """
         Regressions test for ticket 15103 - filtering on fields defined in a
@@ -2378,10 +2409,9 @@ class AdminSearchTest(TestCase):
         """Ensure that the to_field GET parameter is preserved when a search
         is performed. Refs #10918.
         """
-        from django.contrib.admin.views.main import TO_FIELD_VAR
+        response = self.client.get('/test_admin/admin/auth/user/?q=joe&%s=id' % TO_FIELD_VAR)
-        response = self.client.get('/test_admin/admin/auth/user/?q=joe&%s=username' % TO_FIELD_VAR)
         self.assertContains(response, "\n1 user\n")
-        self.assertContains(response, '<input type="hidden" name="_to_field" value="username"/>', html=True)
+        self.assertContains(response, '<input type="hidden" name="%s" value="id"/>' % TO_FIELD_VAR, html=True)
 
     def test_exact_matches(self):
         response = self.client.get('/test_admin/admin/admin_views/recommendation/?q=bar')