In FreeBSD 12.0-STABLE before r349628, 12.0-RELEASE before 12.0-RELEASE-p7, 11.3-PRERELEASE before r349629, 11.3-RC3 before 11.3-RC3-p1, and 11.2-RELEASE before 11.2-RELEASE-p11, a bug in the cdrom driver allows users with read access to the cdrom device to arbitrarily overwrite kernel memory when media is present thereby allowing a malicious user in the operator group to gain root privileges.
https://security.FreeBSD.org/advisories/FreeBSD-SA-19:11.cd_ioctl.asc
http://packetstormsecurity.com/files/153522/FreeBSD-Security-Advisory-FreeBSD-SA-19-11.cd_ioctl.html