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

Summary

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.

Details

Root cause (verified at 26b6b10)

1. Events route — authenticated, feature-flagged, no share-scope check (routers/router.go):

file := v4.Group("file"); file.Use(middleware.RequiredScopes(types.ScopeFilesRead))
file.GET("events",
    middleware.LoginRequired(),
    middleware.IsFunctionEnabled(func(c *gin.Context) bool { return dep.SettingProvider().EventHubEnabled(c) }),
    controllers.FromQuery[explorer.ExplorerEventService](...), controllers.HandleExplorerEventsPush)

EventHubEnabled defaults true (inventory/setting.go: "fs_event_push_enabled":"1").

2. Service subscribes to the listed parent's ID (service/explorer/events.go):

parent, _, err := m.List(c, uri, &manager.ListArgs{Page:0, PageSize:1})   // also runs share validity/password
...
rx, resumed, err := eventHub.Subscribe(c, parent.ID(), requestInfo.ClientID)

3. Single-file share Root swaps the share root to the owner parent (share_navigator.go):

n.shareRoot = newFile(nil, share.Edges.File)
...
if n.shareRoot.Type() == types.FileTypeFile {
    n.singleFileShare = true
    n.shareRoot = n.shareRoot.Parent   // <-- owner-side parent folder
}

4. To returns that parent for the bare root URI (share_navigator.go):

elements := path.Elements()
if len(elements) == 1 && n.singleFileShare { return latestSharedSingleFile(...) } // only when URI names the file
...
return current  // current == shareRoot == owner parent folder

The bare root share URI has zero path elements (URI.Elements() returns nil for path /), so the len(elements)==1 guard is skipped and To returns the parent folder. dbfs.List returns that as parent, so parent.ID() is the owner parent folder's real ID.

5. Children masks the broader parent — for singleFileShare it returns only []*File{sharedFile}, so the recipient's listing shows just the shared file even though the subscribed topic is the whole parent.

6. Publication fans out to ancestor topics with only a client-ID filter (dbfs/events.go):

func (f *DBFS) getEligibleSubscriber(ctx, file, checkParentPerm) []foundSubscriber {
    roots := file.Ancestors()
    for _, root := range roots {
        subscribers := f.eventHub.GetSubscribers(ctx, root.Model.ID)
        subscribers = lo.Filter(subscribers, func(s eventhub.Subscriber, _ int) bool {
            return !(requestInfo != nil && s.ID() == requestInfo.ClientID)  // ONLY exclude the causing client
        })
        ...
    }
}
// emit*: From: subscriber.relativePath(file)  // owner-side path of the changed sibling

relativePath trims the changed file's owner path by the subscribed root's owner path, yielding the sibling's name (e.g. /Secret-Plan.pdf). No check that the subscriber is authorized for the changed file or within their share scope.