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 select_for_update(). When using 'self' in the of argument with multi-table inheritance, a parent model was locked instead of the queryset’s model (#30953).