In FreeBSD before 11.2-STABLE(r340854) and 11.2-RELEASE-p5, an integer overflow error can occur when handling the client address length field in an NFSv4 request. Unprivileged remote users with access to the NFS server can crash the system by sending a specially crafted NFSv4 request.
https://security.freebsd.org/advisories/FreeBSD-SA-18:13.nfs.asc
https://secuniaresearch.flexerasoftware.com/secunia_research/2018-24/