When creating content with a very large title or description field, Plone can become unresponsive. Even if the content loads, it can be hard to edit or delete, because the UI is unwieldy.
Plone before 5.2.3 allows SSRF attacks via the tracebacks feature (only available to the Manager role).
Plone before 5.2.3 allows XXE attacks via a feature that is protected by an unapplied permission of plone.schemaeditor.ManageSchemata (therefore, only available to the Manager role).
Plone before 5.2.3 allows XXE attacks via a feature that is explicitly only available to the Manager role.