Errata patches for LibreSSL have been released for OpenBSD 6.6 and 6.7. libcrypto may fail to build a valid certificate chain due to expired untrusted issuer certificates.
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/errata66.html https://www.openbsd.org/errata67.html