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Summary
Confidential computing allows cloud tenants to run sensitive workloads without trusting the cloud service provider. Hardware-based trusted execution environments, such as AMD SEV-SNP, protect these workloads inside Confidential Virtual Machines (CVMs). With Mior, we present a software-only attack that compromises SEV-SNP by redirecting memory accesses of the secure co-processor (PSP) to an attacker-controlled device. The device acts as a substitute for DRAM, allowing the PSP initialization checks to succeed while leaving critical memory protections uninitialized. A malicious hypervisor can then read and modify CVM memory or forge valid attestation reports for any guest.
AMD SEV-SNP
Ordinary virtual machines rely on the hypervisor to isolate tenants. SEV-SNP extends this isolation to protect a guest from the hypervisor itself, using memory encryption and hardware-enforced access control. A central data structure, the Reverse Map Table (RMP), tracks ownership and permissions for physical memory pages. The encryption of guest memory provides confidentiality, while the RMP protects its integrity. The PSP initializes this table and manages security-sensitive guest metadata. This initializaiton is critical. An attacker that can stop this initialization from happening can break all SEV-SNP guarantees.
AMD’s Infinity Fabric
Modern AMD processors connect CPU cores, memory controllers, peripheral devices, and the PSP through the Infinity Fabric. Its Data Fabric routes memory transactions according to configurable address ranges. Some addresses lead to DRAM; others lead to device memory exposed through memory-mapped I/O (MMIO), such as a GPU memory. Different entry points into the fabric can have different routing configurations. As a result, the same physical address can lead to DRAM for one component and to a device for another. Mior exploits this difference between the PSP view of memory and the routing applied to its accesses.
Illustration 1: Mior configures the PSP fabric entry point to route selected addresses to GPU memory, while CPU accesses still reach DRAM.
Mior Overview
Mior operates within the SEV-SNP threat model, where the hypervisor, motherboard firmware (BIOS or UEFI), and peripheral devices are untrusted. We modify the BIOS to leave the relevant Data Fabric configuration registers unlocked. The malicious hypervisor then installs a routing rule at the PSP entry point that redirects selected DRAM accesses to device memory. The hypervisor can carfeully choose rules at other entry points to hide this redirection from the PSP memory-map checks.
The PSP builds its memory map before initializing SEV-SNP. It uses this map to reject addresses that lead to MMIO rather than DRAM. However, the PSP reads routing registers through a broadcast operation that combines the values from different fabric components using a bitwise OR. When these components have different configurations, the combined result can conceal a malicious MMIO range. The PSP therefore accepts addresses as DRAM even though its own accesses to them will reach a device via MMIO.
Illustration 2: Broadcast reads combine routing registers using bitwise OR. A malicious range (RM) at the PSP entry point can be hidden by a benign range (RB) at another entry point. The PSP accepts RM as DRAM even though its accesses reach MMIO.
What can an attacker do with this misrouting? The obvious approach is to drop the PSP writes that initialize the RMP. When we attempted this, however, we find that the PSP reads back the RMP entries after writing them. It would therefor detect the missing values and fail during initialization. Instead, we redirect these accesses to an attacker-controlled PCIe device, such as a commodity GPU. The device memory behaves like DRAM: it stores the values the PSP writes and returns them unchanged on later reads. We call this primitive Device-as-Memory. The read-back check passes, yet the RMP in DRAM, which the CPU uses to enforce isolation, never receives the PSP writes. We apply this to the RMP entries that protect the RMP itself. These entries stay uninitialized, so the hypervisor can modify the rest of the RMP and remove the protection of guest metadata.
We demonstrate two consequences. First, we corrupt encrypted guest metadata to enable debugging on a production CVM, allowing the hypervisor to use the PSP debug commands to read and write guest memory. Second, we copy the encrypted launch measurement that the PSP stores in a benign guest’s metadata into the metadata of a malicious guest. The PSP then signs attestation reports containing the benign measurement, even though the launched image is different. This results in a forged attestation report which does not correctly represent the state of the CVM.
What went wrong?
The PSP security checks rely on a memory map that does not faithfully represent the fabric routing configuration. A bitwise OR of register values cannot describe all the address ranges configured independently across the fabric. Mior exploits this mistake and uses device memory to satisfy the PSP read-back checks. Those checks confirm that data was stored somewhere, but not that it reached the DRAM used by the CPU to enforce isolation. A defense must account for each component’s routing configuration or enforce a consistent configuration across the fabric.
Affected Hardware
We demonstrated the end-to-end attack on an AMD Zen 5 EPYC 9135 processor with SEV-SNP firmware API version 1.58.4. We also confirmed with source-code analysis that Zen 3 and Zen 4 use the same Data Fabric routing configuration logic. However, we did not evaluate the attack experimentally on those generations. We therefore show that Zen 5 is affected by Mior and consider Zen 3 and Zen 4 potentially affected.
FAQ
Q: What are the requirements for the attack?
- The attacker controls the BIOS and hypervisor and can use a PCIe device, such as a GPU, to back redirected memory accesses. These components are outside the SEV-SNP trusted computing base.
Q: Why is Mior an XCA attack?
- Mior corrupts interconnect routing to violate a trusted execution environment security guarantees. It is an instance of the Interconnect Corruption Attacks (XCA) class.
Q: How is Mior different from Fabricked?
- Fabricked drops PSP writes intended to initialize the RMP. Mior hides malicious MMIO routing from the PSP memory map and backs redirected reads and writes with device memory. This lets Mior pass read-back checks that would detect dropped writes.
Q: Why the name MIOR?
- MIOR is a blend word of MMIO and OR, signifying that we use MMIO rerouting and hiding it with the mistaken OR reduction the PSP performs.
Q: Is the attack scenario realistic?
- We operate in the threat model defined for AMD SEV-SNP. AMD explicitly distrusts the hypervisor, and confidential computing specifically aims to protect sensitive data from a potentially malicious cloud provider.
Q: Does Mior affect ordinary virtual machines?
- Mior targets the protection of confidential VMs against their host. Ordinary VMs already trust the hypervisor and platform firmware, so a malicious host can access them without this attack.
Q: Does this affect Intel TDX or Arm CCA?
- We did not evaluate Mior on Intel TDX or Arm CCA. The broader problem of validating memory routing is relevant to other confidential computing architectures, but this paper demonstrates an attack on AMD SEV-SNP.
Q: Does this apply to SEV or SEV-ES?
- We did not evaluate those versions. Unlike SEV-SNP, SEV and SEV-ES do not provide the guest-memory integrity guarantees targeted by Mior.
Q: What was AMD’s response?
- AMD acknowledged the vulnerability and agreed to coordinated disclosure. MIOR has been assigned CVE-2026-0462, and an updated firmware version has been published which mitigates the vulnerability.
Authors
Responsible Disclosure
We reported Mior to AMD on February 12, 2026. AMD acknowledged the vulnerability, and we agreed on an embargo ending November 10, 2026.
CVE & AMD Response
MIOR has been assigned CVE-2026-0462.
Citation
To cite our paper, please use the following BibTeX entry:
BibTeX
@inproceedings{wech2026mior,
title = {{Mior: Breaking AMD SEV-SNP with Device-as-Memory}},
author = {Chris Wech and Philipp Giersfeld and Benedict Schlüter and Shweta Shinde},
booktitle = {Proceedings of the 2026 ACM SIGSAC Conference on Computer and Communications Security},
year = {2026},
month = nov,
address = {The Hague, Netherlands},
publisher = {Association for Computing Machinery},
doi = {10.1145/3830454.3846723},
}