grub2-bhyve, as used in FreeBSD bhyve before revision 525916 2020-02-12, does not validate the address provided as part of a memrw command (read_ or write_) by a guest through a grub2.cfg file. This allows an untrusted guest to perform arbitrary read or write operations in the context of the grub-bhyve process, resulting in code execution as root on the host OS.