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>

django/forms/widgets.py

@@ -406,17 +406,41 @@ class MultipleHiddenInput(HiddenInput):
 
 
 class FileInput(Input):
+    allow_multiple_selected = False
     input_type = "file"
     needs_multipart_form = True
     template_name = "django/forms/widgets/file.html"
 
+    def __init__(self, attrs=None):
+        if (
+            attrs is not None
+            and not self.allow_multiple_selected
+            and attrs.get("multiple", False)
+        ):
+            raise ValueError(
+                "%s doesn't support uploading multiple files."
+                % self.__class__.__qualname__
+            )
+        if self.allow_multiple_selected:
+            if attrs is None:
+                attrs = {"multiple": True}
+            else:
+                attrs.setdefault("multiple", True)
+        super().__init__(attrs)
+
     def format_value(self, value):
         """File input never renders a value."""
         return
 
     def value_from_datadict(self, data, files, name):
         "File widgets take data from FILES, not POST"
-        return files.get(name)
+        getter = files.get
+        if self.allow_multiple_selected:
+            try:
+                getter = files.getlist
+            except AttributeError:
+                pass
+        return getter(name)
 
     def value_omitted_from_data(self, data, files, name):
         return name not in files