AMD SEV-SNP VMs Fall to Mior and Skyfall Attacks

Mior and Skyfall are two newly disclosed attacks that compromise AMD SEV-SNP protected virtual machines when the host’s hypervisor is malicious. Mior, developed by ETH Zurich researchers, additionally requires control of the server BIOS and a PCIe device such as a graphics card. It exploits initialization of the Reverse Map Table during VM startup to gain memory access and forge attestation reports. The attack was demonstrated on EPYC 9135 processors and potentially affects Zen 3 and Zen 4 chips. Skyfall, from ETH Zurich and Google researchers, builds on Transient Scheduler Attacks that leak data through instruction timing and requires only a compromised hypervisor. The attack recovered register values and disk-encryption keys from test virtual machines on EPYC 7313, 9124, and 9334 processors but did not succeed on Zen 5 chips.

AMD assigned CVE-2026-0462 to Mior (CVSS 5.9) and CVE-2026-40671 to Skyfall (CVSS 4.9). Microcode updates dated August 12 have been released, with platform firmware patches scheduled for November for Skyfall and December for Mior. Cloud customers depend entirely on their providers to install these host firmware fixes, as the patches operate at the host level outside customer control.