New Mior and Skyfall Attacks Let Rogue Cloud Hosts Steal Secrets From AMD SEV-SNP VMs - The Hacker News
Researchers have disclosed two new attacks, Mior and Skyfall, that allow malicious cloud hosts to steal data from AMD SEV-SNP protected virtual machines.
The Mior attack, developed by ETH Zurich researchers, targets AMD SEV-SNP protected virtual machines by redirecting writes from the Platform Security Processor (PSP) during VM startup. This allows attackers to rewrite the Reverse Map Table (RMP) protections, enabling debugging on confidential VMs and reading/writing their memory. The attack has been successfully demonstrated in all 1,000 test attempts.
The researchers also demonstrated how Mior can copy a VM's software measurement from a harmless VM to a malicious one, causing the malicious VM's attestation reports to describe the harmless image instead. This compromises the integrity verification process that SEV-SNP provides.
We operate in AMD's threat model defined for SEV-SNP. AMD explicitly distrusts the UEFI, thus an attacker can modify the UEFI.
Skyfall Attack Details
The Skyfall attack, developed by a joint team from ETH Zurich and Google, exploits Transient Scheduler Attacks (TSA) vulnerabilities in AMD processors. When a hypervisor intentionally causes a VM to fail to start, the processor caches part of the VM's saved state, which the hypervisor can then read through TSA techniques.
This method allowed researchers to recover VM register values and disk encryption keys from test virtual machines. The attack can read specific cache lines in VM memory but cannot access the entire page. Unlike Mior, Skyfall doesn't require tampering with hardware, only a malicious hypervisor.
Affected Processors and Fixes
AMD has tracked Mior as CVE-2026-0462 (CVSS 4.0 score 5.9) and Skyfall's VM leak as CVE-2026-40671 (CVSS 4.0 score 4.9). Both vulnerabilities affect five EPYC server lines, with fixes implemented through firmware updates. Microcode for Skyfall was released on August 12, with platform firmware updates expected in November.
For the Mior vulnerability, AMD plans to release platform firmware in December. The Instinct MI300A accelerator received a Skyfall patch on September 21, while fixes for embedded EPYC models are scheduled between January and April 2027. Supermicro has published BIOS fixes for affected motherboards and recommends additional BMC firmware updates.
The Skyfall team also discovered a separate vulnerability affecting System Management Mode (SMM) memory, tracked as CVE-2026-18448 (CVSS 4.0 score 5.6). This flaw affects both EPYC and Ryzen chips and requires an EDK II firmware patch expected in November.
Customer Impact
Since the fixes are implemented in the host's firmware, customers who rent confidential VMs depend on their cloud providers to install the updates. AMD's advisories list TCB values for SNP attestation but don't specify how VM owners should verify them. Neither advisory indicates whether the vulnerabilities have been exploited in real attacks.
The Mior proof-of-concept code requires a modified BIOS that leaves memory-routing settings unlocked. Both research teams have published their code, though the Skyfall paper faced criticism from the IEEE program committee for overlooking realistic attack requirements, including processor cores free of other activity and precise timing.
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