**Backgroud** [Januscape](https://github.com/V4bel/Januscape) is a use-after-free vulnerability in the shadow MMU emulation of KVM/x86. It can trigger the bug with guest-side actions alone to corrupt the host kernel's shadow page, and it can threaten the guest-host isolation of KVM/x86 hosts that accept untrusted guests and expose nested virtualization, particularly multi-tenant x86 public clouds (GCP, AWS, etc.). PVM also uses the shadow MMU and is therefore affected as well.