# Django 5.2.17 documentation

# 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 `truncatechars_html` and `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 (#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 (#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:

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