CVE-2026-55499: Cloudreve: Broken Access Control in file event stream: a single-file share recipient is subscribed to the owner's parent folder and receives activity events for unshared siblings

When an authenticated recipient of a single-file share opens the file event stream (GET /api/v4/file/events?uri=<share-root>), Cloudreve validates the URI by listing it and then subscribes the caller to parent.ID(). For a single-file share, the share navigator resolves the bare share-root URI to the owner-side parent folder of the shared file (not the file), while the visible listing is filtered down to just the shared file. The event hub then keys topics by numeric file ID only and, on each file change, fans the event out to subscribers of every ancestor topic, filtering only the client ID that caused the event — never the subscriber’s share scope.

Consequently, a recipient of one shared file can receive Server-Sent Events (type, sibling path/name, rename target, hashed file ID) for other files and subfolders in the owner’s parent folder that were never shared. Contents are not disclosed; file-activity metadata is.