==========================
Django 4.2.1 release notes
==========================

*May 3, 2023*

Django 4.2.1 fixes a security issue with severity "low" and several bugs in
4.2.

CVE-2023-31047: Potential bypass of validation when uploading multiple files using one form field
=================================================================================================

Uploading multiple files using one form field has never been supported by
:class:`.forms.FileField` or :class:`.forms.ImageField` as only the last
uploaded file was validated. Unfortunately, :ref:`uploading_multiple_files`
topic suggested otherwise.

In order to avoid the vulnerability, :class:`~django.forms.ClearableFileInput`
and :class:`~django.forms.FileInput` form widgets now raise ``ValueError`` when
the ``multiple`` HTML attribute is set on them. To prevent the exception and
keep the old behavior, set ``allow_multiple_selected`` to ``True``.

For more details on using the new attribute and handling of multiple files
through a single field, see :ref:`uploading_multiple_files`.

Bugfixes
========

* Fixed a regression in Django 4.2 that caused a crash of ``QuerySet.defer()``
  when deferring fields by attribute names (:ticket:`34458`).

* Fixed a regression in Django 4.2 that caused a crash of
  :class:`~django.contrib.postgres.search.SearchVector` function with ``%``
  characters (:ticket:`34459`).

* Fixed a regression in Django 4.2 that caused aggregation over query that
  uses explicit grouping to group against the wrong columns (:ticket:`34464`).

* Reallowed, following a regression in Django 4.2, setting the
  ``"cursor_factory"`` option in :setting:`OPTIONS` on PostgreSQL
  (:ticket:`34466`).

* Enforced UTF-8 client encoding on PostgreSQL, following a regression in
  Django 4.2 (:ticket:`34470`).

* Fixed a regression in Django 4.2 where ``i18n_patterns()`` didn't respect the
  ``prefix_default_language`` argument when a fallback language of the default
  language was used (:ticket:`34455`).

* Fixed a regression in Django 4.2 where translated URLs of the default
  language from ``i18n_patterns()`` with ``prefix_default_language`` set to
  ``False`` raised 404 errors for a request with a different language
  (:ticket:`34515`).

* Fixed a regression in Django 4.2 where creating copies and deep copies of
  ``HttpRequest``, ``HttpResponse``, and their subclasses didn't always work
  correctly (:ticket:`34482`, :ticket:`34484`).

* Fixed a regression in Django 4.2 where ``timesince`` and ``timeuntil``
  template filters returned incorrect results for a datetime with a non-UTC
  timezone when a time difference is less than 1 day (:ticket:`34483`).

* Fixed a regression in Django 4.2 that caused a crash of
  :class:`~django.contrib.postgres.search.SearchHeadline` function with
  ``psycopg`` 3 (:ticket:`34486`).

* Fixed a regression in Django 4.2 that caused incorrect ``ClearableFileInput``
  margins in the admin (:ticket:`34506`).

* Fixed a regression in Django 4.2 where breadcrumbs didn't appear on admin
  site app index views (:ticket:`34512`).

* Made squashing migrations reduce ``AddIndex``, ``RemoveIndex``,
  ``RenameIndex``, and ``CreateModel`` operations which allows removing a
  deprecated ``Meta.index_together`` option from historical migrations and use
  ``Meta.indexes`` instead (:ticket:`34525`).