File Browser: Cross-user unauthorized share-link deletion via unbounded prefix match in DeleteWithPathPrefix

Summary

A low-privileged authenticated user of filebrowser (with create + delete permissions in their own isolated scope) can silently destroy share-link records belonging to any other user — including the administrator — by performing a legitimate DELETE on a file in their own directory whose logical path happens to be a byte-prefix of another user's stored share.Link.Path. The file contents of the victim are not exposed, but the victim's share links are irrevocably wiped.

Details

resourceDeleteHandler in http/resource.go cleans up any share records that reference a deleted file by calling:

// http/resource.go
err = d.store.Share.DeleteWithPathPrefix(file.Path)

file.Path here is the *logical* path from the URL of the deleting user's request (e.g. /a), not the absolute filesystem path. It is passed as-is to the bolt backend:

// storage/bolt/share.go
func (s shareBackend) DeleteWithPathPrefix(pathPrefix string) error {
    var links []share.Link
    if err := s.db.Prefix("Path", pathPrefix, &links); err != nil {
        return err
    }
    for _, link := range links {
        err = errors.Join(err, s.db.DeleteStruct(&share.Link{Hash: link.Hash}))
    }
    return err
}

Why the design contradicts this behavior. share.Link carries a UserID field and the application elsewhere treats shares as per-user owned resources. shareDeleteHandler explicitly enforces link.UserID != d.user.ID && !d.user.Perm.Admin → 403. The file-deletion side-effect path is the only location that bypasses this rule.

### Impact - Integrity: unauthorized deletion of share-link metadata belonging to arbitrary users, including administrators. - Availability: effective denial-of-service of the share-link feature — a cooperating (or malicious) low-priv user can wipe the bulk of existing share links by iterating a short set of one- and two-character prefixes.