New Mior and Skyfall Attacks Compromise AMD SEV-SNP Security

Researchers have identified two new security flaws, named Mior and Skyfall, that allow malicious hosts to bypass AMD’s Secure Encrypted Virtualization-Secure Nested Paging (SEV-SNP) protections. These attacks enable an attacker with control over a server’s hypervisor to read sensitive data within protected virtual machines (VMs) that were specifically designed to remain isolated from the host operator.

Mior Attack Targets Memory and Attestation

Discovered by a research team at ETH Zurich, the Mior attack exploits vulnerabilities during the VM startup process. By manipulating how the Platform Security Processor (PSP) interacts with memory, researchers demonstrated they could redirect writes to a controlled graphics card rather than main memory. This allows the hypervisor to rewrite protections in the Reverse Map Table (RMP), which is responsible for memory ownership and access control.

Mior can be used to enable debugging on a confidential VM, allowing the attacker to read and write the VM’s memory. Additionally, the attack can compromise the attestation process; researchers were able to copy a harmless VM’s measurement into a malicious VM, causing the system to generate signed reports that falsely claim the malicious software is legitimate. The Mior attack is tracked as CVE-2026-0462 and has a CVSS score of 5.9. Successful exploitation requires control over both the server’s hypervisor and the BIOS (UEFI).

Skyfall Leaks Encryption Keys via Timing

A separate team from ETH Zurich and Google disclosed Skyfall, an attack that builds upon Transient Scheduler Attacks (TSA), a known class of flaws in AMD processors that leak data through instruction timing. Skyfall exploits the way a processor caches a VM’s saved state when a hypervisor intentionally causes a VM to fail to start.

By using this method, the researchers successfully recovered VM register values and disk-encryption keys. While Skyfall is more limited than Mior in the amount of memory it can access, it remains a significant risk. It can also read decrypted microcode updates and register values stored in System Management Mode (SMM) memory, which are typically inaccessible to the operating system kernel. The VM-specific leak is tracked as CVE-2026-40671, with a CVSS score of 4.9.

Mitigation and Affected Hardware

The vulnerabilities primarily affect AMD EPYC server processors. While the researchers noted that the Skyfall leak was not demonstrated on newer Zen 5 chips, it was successfully tested on Zen 3 and Zen 4 architectures.

AMD has released SEV firmware and microcode updates to address these flaws. However, because many of these fixes are implemented at the platform firmware level, the responsibility for deployment often lies with server manufacturers and cloud providers. Customers using confidential computing services in the cloud are dependent on their providers to install the necessary BIOS and firmware updates to ensure the security of their workloads.