Chip maker AMD has issued guidance for attacks CVE-2020-12967, CVE-2021-26311 that allow bypassing the SEV- Secure Encrypted Virtualization technology implemented to prevent rogue operating systems on virtual machines

AMD SEV isolates virtual machines and the hypervisor, but the two attacks can allow threat actors to inject arbitrary code into the virtual machine even if the protection mechanism is in place.

The first flaw, tracked as CVE-2020-12967, is caused by the lack of nested page table protection in the AMD SEV/SEV-ES feature which could potentially lead to arbitrary code execution within the guest VM if a malicious administrator has access to compromise the server hypervisor.

The second vulnerability, tracked as CVE-2021-26311, resides in the AMD SEV/SEV-ES feature. The memory can be rearranged in the guest address space that is not detected by the attestation mechanism which could be used by a malicious hypervisor to potentially lead to arbitrary code execution within the guest VM if a malicious administrator has access to compromise the server hypervisor.

The vulnerabilities impact all AMD EPYC processors, 1st/2nd/3rd Gen AMD EPYC Processors and AMD EPYC Embedded Processors.

The vendor has provided mitigation in the SEV-SNP feature which is available for enablement in 3rd Gen AMD EPYC processors. Customers could mitigate the attacks by enabling SEV-SNP, which is only supported on 3rd Gen AMD EPYC.