Errata patches for vmm have been released for OpenBSD 6.6. A missing range check in the vmm pvclock allows a guest to write to host memory.
Binary updates for the amd64 platform are available via the syspatch utility. Source code patches can be found on the errata page: https://www.openbsd.org/errata66.html As these affect the kernel, a reboot will be needed after patching.
