django CMS: Clipboard copy IDOR discloses unauthorized plugin content

Summary

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.

Details

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.)

Impact

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.

Patches

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.

Workarounds

None. Upgrade is recommended.

Credits

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