HyperKit is a toolkit for embedding hypervisor capabilities in an application. In versions 0.20210107 and prior of HyperKit, ` vi_pci_write` has is a call to `vc_cfgwrite` that does not check for null which when called makes the host crash. This issue may lead to a guest crashing the host causing a denial of service. This issue is fixed in commit 451558fe8aaa8b24e02e34106e3bb9fe41d7ad13.