In FreeBSD 12.0-STABLE before r350222, 12.0-RELEASE before 12.0-RELEASE-p8, 11.3-STABLE before r350223, 11.3-RELEASE before 11.3-RELEASE-p1, and 11.2-RELEASE before 11.2-RELEASE-p12, rights transmitted over a domain socket did not properly release a reference on transmission error allowing a malicious user to cause the reference counter to wrap, forcing a free event. This could allow a malicious local user to gain root privileges or escape from a jail.
https://security.netapp.com/advisory/ntap-20190814-0003/
https://security.FreeBSD.org/advisories/FreeBSD-SA-19:17.fd.asc
http://packetstormsecurity.com/files/153755/FreeBSD-Security-Advisory-FreeBSD-SA-19-17.fd.html