Refs CVE-2026-1312 -- Raised ValueError when FilteredRelation aliases contain periods.

This prevents failures at the database layer, given that aliases in the
ON clause are not quoted.

Systematically quoting aliases even in FilteredRelation is tracked in
https://code.djangoproject.com/ticket/36795.

3 files changed, 26 insertions, 3 deletions

diff --git a/django/db/models/sql/query.py b/django/db/models/sql/query.py
index c6f080dcbb..7a4cf843c1 100644
--- a/django/db/models/sql/query.py
+++ b/django/db/models/sql/query.py
@@ -1720,6 +1720,11 @@ class Query(BaseExpression):
         return target_clause, needed_inner
 
     def add_filtered_relation(self, filtered_relation, alias):
+        if "." in alias:
+            raise ValueError(
+                "FilteredRelation doesn't support aliases with periods "
+                "(got %r)." % alias
+            )
         self.check_alias(alias)
         filtered_relation.alias = alias
         relation_lookup_parts, relation_field_parts, _ = self.solve_lookup_type(
diff --git a/tests/filtered_relation/tests.py b/tests/filtered_relation/tests.py
index cdcd5c19af..e263307193 100644
--- a/tests/filtered_relation/tests.py
+++ b/tests/filtered_relation/tests.py
@@ -216,6 +216,19 @@ class FilteredRelationTests(TestCase):
             str(queryset.query),
         )
 
+    def test_period_forbidden(self):
+        msg = (
+            "FilteredRelation doesn't support aliases with periods (got 'book.alice')."
+        )
+        with self.assertRaisesMessage(ValueError, msg):
+            Author.objects.annotate(
+                **{
+                    "book.alice": FilteredRelation(
+                        "book", condition=Q(book__title__iexact="poem by alice")
+                    )
+                }
+            )
+
     def test_multiple(self):
         qs = (
             Author.objects.annotate(
diff --git a/tests/ordering/tests.py b/tests/ordering/tests.py
index afe2e3c22c..008f0239b3 100644
--- a/tests/ordering/tests.py
+++ b/tests/ordering/tests.py
@@ -18,7 +18,6 @@ from django.db.models import (
     When,
 )
 from django.db.models.functions import Length, Upper
-from django.db.utils import DatabaseError
 from django.test import TestCase
 
 from .models import (
@@ -411,13 +410,19 @@ class OrderingTests(TestCase):
         self.assertNotEqual(qs[0].headline, "Backdated")
 
         relation = FilteredRelation("author")
-        qs2 = Article.objects.annotate(**{crafted: relation}).order_by(crafted)
-        with self.assertRaises(DatabaseError):
+        msg = (
+            "FilteredRelation doesn't support aliases with periods "
+            "(got 'ordering_article.pub_date')."
+        )
+        with self.assertRaisesMessage(ValueError, msg):
+            qs2 = Article.objects.annotate(**{crafted: relation}).order_by(crafted)
             # Before, unlike F(), which causes ordering expressions to be
             # replaced by ordinals like n in ORDER BY n, these were ordered by
             # pub_date instead of author.
             # The Article model orders by -pk, so sorting on author will place
             # first any article by author2 instead of the backdated one.
+            # This assertion is reachable if FilteredRelation.__init__() starts
+            # supporting periods in aliases in the future.
             self.assertNotEqual(qs2[0].headline, "Backdated")
 
     def test_order_by_pk(self):