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Django 2.1.15 release notes

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*December 2, 2019*

Django 2.1.15 fixes a security issue and a data loss bug in 2.1.14.

CVE-2019-19118: Privilege escalation in the Django admin.

=========================================================

Since Django 2.1, a Django model admin displaying a parent model with related

model inlines, where the user has view-only permissions to a parent model but

edit permissions to the inline model, would display a read-only view of the

parent model but editable forms for the inline.

Submitting these forms would not allow direct edits to the parent model, but

would trigger the parent model's ``save()`` method, and cause pre and post-save

signal handlers to be invoked. This is a privilege escalation as a user who

lacks permission to edit a model should not be able to trigger its save-related

signals.

To resolve this issue, the permission handling code of the Django admin

interface has been changed. Now, if a user has only the "view" permission for a

parent model, the entire displayed form will not be editable, even if the user

has permission to edit models included in inlines.

This is a backwards-incompatible change, and the Django security team is aware

that some users of Django were depending on the ability to allow editing of

inlines in the admin form of an otherwise view-only parent model.

Given the complexity of the Django admin, and in-particular the permissions

related checks, it is the view of the Django security team that this change was

necessary: that it is not currently feasible to maintain the existing behavior

while escaping the potential privilege escalation in a way that would avoid a

recurrence of similar issues in the future, and that would be compatible with

Django's *safe by default* philosophy.

For the time being, developers whose applications are affected by this change

should replace the use of inlines in read-only parents with custom forms and

views that explicitly implement the desired functionality. In the longer term,

adding a documented, supported, and properly-tested mechanism for

partially-editable multi-model forms to the admin interface may occur in Django

itself.

Bugfixes

========

* Fixed a data loss possibility in the

  :meth:`~django.db.models.query.QuerySet.select_for_update()`. When using

  ``'self'`` in the ``of`` argument with :ref:`multi-table inheritance

  <multi-table-inheritance>`, a parent model was locked instead of the

  queryset's model (:ticket:`30953`).