For FreeBSD users out there, I would seem that, in the default setting, the mysqld_safe script is being run as mysql uid by the rc startup script. So by the time mysqld_safe is invoked, root privileges are already dropped.

But that shouldn't dissuade one from taking some preventive measures, e.g. making sure that unnecessary FILE privileges are revoked from accounts and/or making sure that my.cnf is owned by root and only writable by root. Also, as the CVE mentions, do remember that a my.cnf in /var/db/mysql (or /var/lib/mysql for Linux) will override settings in other locations. Touching it as root with an appropriate flag mask should plug that hole too.

An updated mysql package will be soon be available of course.