Folder::uploadableBy() returned true for any staff member without looking
at the folder, on the strength of a comment saying staff had already
validated folder_id through FilesController's own flow. No upload path
did. FilesController::store() did not check the folder at all; the two
that called uploadableBy() — the API upload and the chunked upload the
browser actually posts to — called a guard that could only ever say yes.
A client-scoped staff member could therefore name any folder id and put
the file inside a subtree shared with somebody else's client, where
File::scopeVisibleToClient hands it over without an assignment row ever
being written. That is the boundary StaffLibraryScope's own docblock
claims to hold everywhere.
The staff branch now asks StaffLibraryScope::allowsFolder, which returns
true for unscoped staff, so nothing changes for them. The client branch
is untouched: a client is never client-scoped, and ownership or a public
folder opting into client uploads remains the whole of their rule.
The two folder pickers that fed those ids are narrowed the same way the
listings around them already are.
denkfabrik-li