New attacks expose secrets in AMD SEV-SNP cloud VMs

Two new attacks disclosed this week let a rogue cloud host read data from AMD SEV-SNP protected VMs, and in Mior’s case also manipulate memory and forge the signed runtime report. The ETH Zurich team behind Mior demonstrated readings, memory writes, and a forged attestation across SEV-SNP VMs, requiring control of the hypervisor and the BIOS (UEFI) plus a PCIe device such as a graphics card.

In a separate Skyfall release, researchers showed that the attacker can read only three fixed cache lines within a VM page and, in some setups, extract the VM’s saved state or a disk encryption key via transient scheduling techniques. Both attacks were validated in lab tests on AMD EPYC processors, with Mior tested on an EPYC 9135 (Zen 5) and Skyfall demonstrated on Zen 3 and Zen 4 chips; Zen 5 appeared unaffected in their tests.

AMD has linked the findings to two advisories detailing distinct CVEs. Mior is tracked as CVE-2026-0462 and is described as affecting SEV-SNP; Skyfall is tracked as CVE-2026-40671 and described as exposing VM register data. The researchers note that fixes are being rolled out as firmware updates: Mior’s platform firmware and SEV firmware dated 12 August, with platform firmware updates slated for December and Skyfall platform firmware for November, alongside broader embedded chip mitigations planned for 2027.

The advisories also mention that mitigations are delivered via BIOS updates from server makers and require careful coordination with cloud providers for hosted confidential VMs. The Skyfall team additionally references an EDK II advisory that ties the CVE-2026-18448 SMM leakage to missing TSA mitigations in that firmware, with patches due in November for the affected EPYC lines.