In FreeBSD before 11.2-STABLE(r340854) and 11.2-RELEASE-p5, an integer overflow error when handling opcodes can cause memory corruption by sending a specially crafted NFSv4 request. Unprivileged remote users with access to the NFS server may be able to execute arbitrary code.
https://security.freebsd.org/advisories/FreeBSD-SA-18:13.nfs.asc
https://secuniaresearch.flexerasoftware.com/secunia_research/2018-25/