ntopng: Missing Authorization on System Configuration Backup Download and Listing

ntopng is a web-based network traffic monitoring application. Prior to 6.7.260718, scripts/lua/rest/v2/get/system/configurations/list_available_backups.lua and scripts/lua/rest/v2/get/system/configurations/download_backup.lua allow any authenticated non-admin user to list and download system-configuration backups without an administrator check. The download path reaches backup_config.export_backup, and prefs_dump_utils.build_prefs_dump_table includes the ntopng.user.* Redis key space in the backup. A downloaded backup can therefore disclose password hashes for local users and, when configured, API tokens, TOTP secrets, and WebAuthn credential data, enabling account compromise through usable or recoverable credentials. This issue is fixed in version 6.7.260718.