New Mior and Skyfall Attacks Let Rogue Cloud Hosts Steal Secrets From AMD SEV-SNP VMs

Two attacks made public this week allow a malicious host to read data inside AMD SEV-SNP-protected virtual machines (VMs), which are built to keep the server's operator out.

One of them, Mior, can also modify a VM's memory and fake the signed report confirming which software it runs, and both need control of the server's hypervisor, and Mior also needs control of the server's BIOS.

SEV-SNP also measures a VM's software image when the VM starts, and the PSP signs attestation reports that include this measurement.

In a second test, the team copied a harmless VM's measurement into a malicious VM, so the malicious VM's attestation reports described the harmless image instead.

Researchers showed both in lab tests on AMD EPYC server processors, and it plans to give server makers platform firmware in November for Skyfall and in December for Mior, and fixes for embedded chips later.

It uses hardware-enforced memory encryption and access control to protect a VM, even from the host's hypervisor, and the team used a card because it believes the PSP reads the values back to check them, and the card could return them.

The team then enabled debugging on a confidential VM that had it disabled and used the PSP's own debug commands to read and write the VM's memory.

For the key, it changed the VM's kernel to pause at the moment the key sat in registers.

It also recovered register values stored in System Management Mode (SMM) memory, which even the operating system kernel normally cannot read.

Customers are told to get the BIOS update from their server maker, and mior is a separate flaw, unrelated to Fabricked and to the fix for it, the team says.

Beyond VMs, the Skyfall team read decrypted microcode updates on all three test chips.

The Instinct MI300A accelerator has a Skyfall patch dated September 21, and fixes for embedded EPYC models are due between January and April 2027.