The clipboard copy paths of the copy plugins admin endpoint validate only the target (the user's own clipboard) and skip source-side authorization. A staff user can copy plugins out of a placeholder they have no permission on into their clipboard, then read the (secret) content.

In cms/admin/placeholderadmin.py, copy plugin to clipboard and copy placeholder to clipboard check has copy plugins permission, which only evaluates request.toolbar.clipboard.has add plugins permission(...) — the clipboard belongs to the requesting user, and check source is likewise applied only to the clipboard. The source placeholder identified by the attacker-supplied source placeholder id / source plugin id is never authorization-checked. (The placeholder-to-placeholder copy path, has copy from placeholder permission, correctly checks both sides.)

A staff user holding the global add permission for a plugin type, but with no access to a given placeholder/page, can copy that placeholder's plugins into their own clipboard and read content (e.g. link names/URLs, text) they cannot reach through the normal edit endpoints.

Requires CMS PERMISSION=True with per-placeholder/page restrictions.

Fixed in 5.0.8: the clipboard copy paths now also verify source-side permission (has add plugins permission + check source on the source placeholder), matching placeholder-to-placeholder copy.

None. Upgrade is recommended.

Reported by the security team at the University of Sydney ([@reporter]).