Ispconfig(apache) Breaks on bad format SSL certificate
Bad Format SSL breaks Apache. I dont Know but if is possible, i think you need verify SSL before adding, because a bad ssl file will break apache and the only way to fix is delete manualy from vhost. When the DOS Happens one faulty apache process must be killed before restoring service.
Maybe you can verify on ssl save, if apache is working if not kill apache, delete certificates from vhost and restore apache again.