django/django

==========================
Django 4.2.6 release notes
==========================

*October 4, 2023*

Django 4.2.6 fixes a security issue with severity "moderate" and several bugs
in 4.2.5.

CVE-2023-43665: Denial-of-service possibility in ``django.utils.text.Truncator``
================================================================================

Following the fix for :cve:`2019-14232`, the regular expressions used in the
implementation of ``django.utils.text.Truncator``'s ``chars()`` and ``words()``
methods (with ``html=True``) were revised and improved. However, these regular
expressions still exhibited linear backtracking complexity, so when given a
very long, potentially malformed HTML input, the evaluation would still be
slow, leading to a potential denial of service vulnerability.

The ``chars()`` and ``words()`` methods are used to implement the
:tfilter:`truncatechars_html` and :tfilter:`truncatewords_html` template
filters, which were thus also vulnerable.

The input processed by ``Truncator``, when operating in HTML mode, has been
limited to the first five million characters in order to avoid potential
performance and memory issues.

Bugfixes
========

* Fixed a regression in Django 4.2.5 where overriding the deprecated
  ``DEFAULT_FILE_STORAGE`` and ``STATICFILES_STORAGE`` settings in tests caused
  the main ``STORAGES`` to mutate (:ticket:`34821`).

* Fixed a regression in Django 4.2 that caused unnecessary casting of string
  based fields (``CharField``, ``EmailField``, ``TextField``, ``CICharField``,
  ``CIEmailField``, and ``CITextField``) used with the ``__isnull`` lookup on
  PostgreSQL. As a consequence, indexes using an ``__isnull`` expression or
  condition created before Django 4.2 wouldn't be used by the query planner,
  leading to a performance regression (:ticket:`34840`).

  You may need to recreate such indexes created in your database with Django
  4.2 to 4.2.5, as they contain unnecessary ``::text`` casting. Find candidate
  indexes with this query:

  .. code-block:: sql

        SELECT indexname, indexdef
        FROM pg_indexes
        WHERE indexdef LIKE '%::text IS %NULL';