This is a DoS in the OpenBSD kernel (OpenBSD 6.3/6.2) that yields a triple fault. It can be triggered by an unprivileged user. The issue was anounced in OpenBSD 6.3 errata 015 and assigned CVE-2018-14775. There is a very detailed write-up of the issue by Michal Necasek, who discovered the same bug around the same time as I did.