Errata patches for su have been released for OpenBSD 6.5 and 6.6. A user can log in with a different user's login class.
Binary updates for the amd64, i386, and arm64 platforms are available via the syspatch utility. Source code patches can be found on the respective errata page: https://www.openbsd.org/errata65.html https://www.openbsd.org/errata66.html
