Sure, but that requires you to either already have an admin password, or be able to reboot the machine into recovery mode and retain control of it (which typica

Sure, but that requires you to either already have an admin password, or be able to reboot the machine into recovery mode and retain control of it (which typically implies actual physical access). The privilege escalation exploit mentioned in the OP, while technically not remotely exploitable, can be used by malware with lower privileges (i.e. malware running as an unprivileged user, which got onto the machine either through a remote exploit or some sort of drive-by download) to silently elevate itself to root. That's something that shouldn't be possible.