[4.2.x] 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>

3 files changed, 116 insertions, 1 deletions

diff --git a/tests/forms_tests/field_tests/test_filefield.py b/tests/forms_tests/field_tests/test_filefield.py
index 56aaa311e0..00c74a7c1a 100644
--- a/tests/forms_tests/field_tests/test_filefield.py
+++ b/tests/forms_tests/field_tests/test_filefield.py
@@ -2,7 +2,8 @@ import pickle
 
 from django.core.exceptions import ValidationError
 from django.core.files.uploadedfile import SimpleUploadedFile
-from django.forms import FileField
+from django.core.validators import validate_image_file_extension
+from django.forms import FileField, FileInput
 from django.test import SimpleTestCase
 
 
@@ -109,3 +110,68 @@ class FileFieldTest(SimpleTestCase):
 
     def test_file_picklable(self):
         self.assertIsInstance(pickle.loads(pickle.dumps(FileField())), FileField)
+
+
+class MultipleFileInput(FileInput):
+    allow_multiple_selected = True
+
+
+class MultipleFileField(FileField):
+    def __init__(self, *args, **kwargs):
+        kwargs.setdefault("widget", MultipleFileInput())
+        super().__init__(*args, **kwargs)
+
+    def clean(self, data, initial=None):
+        single_file_clean = super().clean
+        if isinstance(data, (list, tuple)):
+            result = [single_file_clean(d, initial) for d in data]
+        else:
+            result = single_file_clean(data, initial)
+        return result
+
+
+class MultipleFileFieldTest(SimpleTestCase):
+    def test_file_multiple(self):
+        f = MultipleFileField()
+        files = [
+            SimpleUploadedFile("name1", b"Content 1"),
+            SimpleUploadedFile("name2", b"Content 2"),
+        ]
+        self.assertEqual(f.clean(files), files)
+
+    def test_file_multiple_empty(self):
+        f = MultipleFileField()
+        files = [
+            SimpleUploadedFile("empty", b""),
+            SimpleUploadedFile("nonempty", b"Some Content"),
+        ]
+        msg = "'The submitted file is empty.'"
+        with self.assertRaisesMessage(ValidationError, msg):
+            f.clean(files)
+        with self.assertRaisesMessage(ValidationError, msg):
+            f.clean(files[::-1])
+
+    def test_file_multiple_validation(self):
+        f = MultipleFileField(validators=[validate_image_file_extension])
+
+        good_files = [
+            SimpleUploadedFile("image1.jpg", b"fake JPEG"),
+            SimpleUploadedFile("image2.png", b"faux image"),
+            SimpleUploadedFile("image3.bmp", b"fraudulent bitmap"),
+        ]
+        self.assertEqual(f.clean(good_files), good_files)
+
+        evil_files = [
+            SimpleUploadedFile("image1.sh", b"#!/bin/bash -c 'echo pwned!'\n"),
+            SimpleUploadedFile("image2.png", b"faux image"),
+            SimpleUploadedFile("image3.jpg", b"fake JPEG"),
+        ]
+
+        evil_rotations = (
+            evil_files[i:] + evil_files[:i]  # Rotate by i.
+            for i in range(len(evil_files))
+        )
+        msg = "File extension “sh” is not allowed. Allowed extensions are: "
+        for rotated_evil_files in evil_rotations:
+            with self.assertRaisesMessage(ValidationError, msg):
+                f.clean(rotated_evil_files)
diff --git a/tests/forms_tests/widget_tests/test_clearablefileinput.py b/tests/forms_tests/widget_tests/test_clearablefileinput.py
index 4fbaec0910..a9b0667ca9 100644
--- a/tests/forms_tests/widget_tests/test_clearablefileinput.py
+++ b/tests/forms_tests/widget_tests/test_clearablefileinput.py
@@ -242,3 +242,8 @@ class ClearableFileInputTest(WidgetTest):
             '<input type="file" name="clearable_file" id="id_clearable_file"></div>',
             form.render(),
         )
+
+    def test_multiple_error(self):
+        msg = "ClearableFileInput doesn't support uploading multiple files."
+        with self.assertRaisesMessage(ValueError, msg):
+            ClearableFileInput(attrs={"multiple": True})
diff --git a/tests/forms_tests/widget_tests/test_fileinput.py b/tests/forms_tests/widget_tests/test_fileinput.py
index ea73e577ce..a49f481728 100644
--- a/tests/forms_tests/widget_tests/test_fileinput.py
+++ b/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)