Errata patches for Xorg have been released for OpenBSD 6.6 and 6.7. Various X server extensions had deficient input validation.
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