sshd in OpenSSH before 7.4, when privilege separation is not used, creates forwarded Unix-domain sockets as root, which might allow local users to gain privileges via unspecified vectors, related to serverloop.c.
http://packetstormsecurity.com/files/140262/OpenSSH-Local-Privilege-Escalation.html
https://bugs.chromium.org/p/project-zero/issues/detail?id=1010
https://cert-portal.siemens.com/productcert/pdf/ssa-412672.pdf
https://github.com/openbsd/src/commit/c76fac666ea038753294f2ac94d310f8adece9ce
https://security.FreeBSD.org/advisories/FreeBSD-SA-17:01.openssh.asc
https://security.netapp.com/advisory/ntap-20171130-0002/
https://support.hpe.com/hpsc/doc/public/display?docLocale=en_US&docId=emr_na-hpesbux03818en_us
https://www.exploit-db.com/exploits/40962/