OpenBSD 6.6, in a non-default configuration where S/Key or YubiKey authentication is enabled, allows local users to become root by leveraging membership in the auth group. This occurs because root’s file can be written to /etc/skey or /var/db/yubikey, and need not be owned by root.
packetstormsecurity.com/files/155572/Qualys-Security-Advisory-OpenBSD-Authentication-Bypass-Privilege-Escalation.html
seclists.org/fulldisclosure/2019/Dec/14
www.openwall.com/lists/oss-security/2019/12/04/5
seclists.org/bugtraq/2019/Dec/8
www.openbsd.org/errata66.html
www.openwall.com/lists/oss-security/2019/12/04/5