If you’ve been following Github you’ve probably noticed by now that latest commits have had some security issues, mainly related to closing dead connections. In some cases attackers could overload the server causing high CPU usage by sending invalid or bad packets, even cause crashes.
What can you do? What should you do? Simple, just update to latest BungeeCord or Waterfall, since they’ve both already received updates and if you’re interested in this specific issue you can find more information about it on Github: https://github.com/SpigotMC/BungeeCord/pull/2908