Fixed CVE-2023-31047, Fixed #31710 -- Prevented potential bypass of validation when uploading multiple files using one form field.

Thanks Moataz Al-Sharida and nawaik for reports.

Co-authored-by: Shai Berger <shai@platonix.com>
Co-authored-by: nessita <124304+nessita@users.noreply.github.com>

tests/forms_tests/widget_tests/test_fileinput.py

@@ -1,4 +1,6 @@
+from django.core.files.uploadedfile import SimpleUploadedFile
 from django.forms import FileField, FileInput, Form
+from django.utils.datastructures import MultiValueDict
 
 from .base import WidgetTest
 
@@ -48,3 +50,45 @@ class FileInputTest(WidgetTest):
             'name="field" required type="file"></div>',
             form.render(),
         )
+
+    def test_multiple_error(self):
+        msg = "FileInput doesn't support uploading multiple files."
+        with self.assertRaisesMessage(ValueError, msg):
+            FileInput(attrs={"multiple": True})
+
+    def test_value_from_datadict_multiple(self):
+        class MultipleFileInput(FileInput):
+            allow_multiple_selected = True
+
+        file_1 = SimpleUploadedFile("something1.txt", b"content 1")
+        file_2 = SimpleUploadedFile("something2.txt", b"content 2")
+        # Uploading multiple files is allowed.
+        widget = MultipleFileInput(attrs={"multiple": True})
+        value = widget.value_from_datadict(
+            data={"name": "Test name"},
+            files=MultiValueDict({"myfile": [file_1, file_2]}),
+            name="myfile",
+        )
+        self.assertEqual(value, [file_1, file_2])
+        # Uploading multiple files is not allowed.
+        widget = FileInput()
+        value = widget.value_from_datadict(
+            data={"name": "Test name"},
+            files=MultiValueDict({"myfile": [file_1, file_2]}),
+            name="myfile",
+        )
+        self.assertEqual(value, file_2)
+
+    def test_multiple_default(self):
+        class MultipleFileInput(FileInput):
+            allow_multiple_selected = True
+
+        tests = [
+            (None, True),
+            ({"class": "myclass"}, True),
+            ({"multiple": False}, False),
+        ]
+        for attrs, expected in tests:
+            with self.subTest(attrs=attrs):
+                widget = MultipleFileInput(attrs=attrs)
+                self.assertIs(widget.attrs["multiple"], expected)