[4.2.x] Fixed CVE-2025-64459 -- Prevented SQL injections in Q/QuerySet via the _connector kwarg.

Thanks cyberstan for the report, Sarah Boyce, Adam Johnson, Simon
Charette, and Jake Howard for the reviews.

Backport of c880530ddd4fabd5939bab0e148bebe36699432a from main.

3 files changed, 16 insertions, 0 deletions

diff --git a/django/db/models/query_utils.py b/django/db/models/query_utils.py
index 5c5644cfb3..a85a682e52 100644
--- a/django/db/models/query_utils.py
+++ b/django/db/models/query_utils.py
@@ -44,8 +44,12 @@ class Q(tree.Node):
     XOR = "XOR"
     default = AND
     conditional = True
+    connectors = (None, AND, OR, XOR)
 
     def __init__(self, *args, _connector=None, _negated=False, **kwargs):
+        if _connector not in self.connectors:
+            connector_reprs = ", ".join(f"{conn!r}" for conn in self.connectors[1:])
+            raise ValueError(f"_connector must be one of {connector_reprs}, or None.")
         super().__init__(
             children=[*args, *sorted(kwargs.items())],
             connector=_connector,
diff --git a/docs/releases/4.2.26.txt b/docs/releases/4.2.26.txt
index ae274c3361..20cf48f05c 100644
--- a/docs/releases/4.2.26.txt
+++ b/docs/releases/4.2.26.txt
@@ -16,3 +16,10 @@ Windows. As a consequence, :class:`~django.http.HttpResponseRedirect`,
 :func:`redirect() <django.shortcuts.redirect>` were subject to a potential
 denial-of-service attack via certain inputs with a very large number of Unicode
 characters (follow up to :cve:`2025-27556`).
+
+CVE-2025-64459: Potential SQL injection via ``_connector`` keyword argument
+===========================================================================
+
+:meth:`.QuerySet.filter`, :meth:`~.QuerySet.exclude`, :meth:`~.QuerySet.get`,
+and :class:`~.Q` were subject to SQL injection using a suitably crafted
+dictionary, with dictionary expansion, as the ``_connector`` argument.
diff --git a/tests/queries/test_q.py b/tests/queries/test_q.py
index cdf40292b0..5f20a41768 100644
--- a/tests/queries/test_q.py
+++ b/tests/queries/test_q.py
@@ -225,6 +225,11 @@ class QTests(SimpleTestCase):
                     Q(*items, _connector=connector),
                 )
 
+    def test_connector_validation(self):
+        msg = f"_connector must be one of {Q.AND!r}, {Q.OR!r}, {Q.XOR!r}, or None."
+        with self.assertRaisesMessage(ValueError, msg):
+            Q(_connector="evil")
+
 
 class QCheckTests(TestCase):
     def test_basic(self):