libc in OpenBSD 6.6 allows authentication bypass via the -schallenge username, as demonstrated by smtpd, ldapd, or radiusd. This is related to gen/auth_subr.c and gen/authenticate.c in libc (and login/login.c and xenocara/app/xenodm/greeter/verify.c).
https://www.openwall.com/lists/oss-security/2019/12/04/5
https://www.openbsd.org/errata66.html
https://seclists.org/bugtraq/2019/Dec/8
http://www.openwall.com/lists/oss-security/2019/12/04/6
http://www.openwall.com/lists/oss-security/2019/12/04/5