Errata patches for the kernel have been released for OpenBSD 6.8. Use of bpf(4) on a carp interface could result in a use after free error.
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/errata68.html As these affect the kernel, a reboot will be needed after patching.