When creating an Image or File with a very large filename, Plone can become unresponsive. Even if the content loads, it can be hard to edit or delete, because the UI is unwieldy.
A privilege escalation issue in plone.app.contenttypes in Plone 4.3 through 5.2.1 allows users to PUT (overwrite) some content without needing write permission.
Plone is vulnerable to reflected cross site scripting and open redirect when an attacker can get a compromised version of the image_view_fullscreen page in a cache, for example in Varnish. The technique is known as cache poisoning. Any later visitor can get redirected when clicking on a link on this page. Usually only anonymous users are affected, but this depends on your cache settings.