Chipmaker AMD Discover Two New Flaws Against its SEV Techonology

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The chipmaker AMD published guidelines for two new attacks (CVE-2020-12967, CVE-2021-26311) against its SEV (Secure Encrypted Virtualization) technology that protects virtual machines from rogue operating systems.

The two attacks, documented in two research papers, respectively titled as “Severity: Code Injection Attacks against Encrypted Virtual Machines” and “undeSErVed trust: Exploiting Permutation-Agnostic Remote Attestation,” can allow cybercriminals to inject arbitrary code into the virtual machine, giving them full control over the VM’s operating system.

The two attacks, SEVurity and undeSErVed, work not only against AMD CPUs protected by SEV but also SEV-ES (Secure Encrypted Virtualization-Encrypted State), an improved version of the technology that AMD released in 2017, a year after adding SEV to its CPUs.

The chipmaker released its security advisory this week because the findings of the two attacks will be presented by two research teams at this year’s 15th IEEE Workshop on Offensive Technologies (WOOT’21).

The first vulnerability, discovered 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. According to the security advisory, 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 chipmaker said all AMP EPYC processors are affected by these vulnerabilities which include 1st/2nd/3rd Gen AMD EPYC™ Processors and AMD EPYC™ Embedded Processors. “The mitigation requires the use of SEV-SNP, which is only supported on 3rd Gen AMD EPYC,” the company added. 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™. 

The researchers revealed the following acknowledgment: 

• CVE-2020-12967: Mathias Morbitzer, Martin Radev and Erick Quintanar Salas from Fraunhofer AISEC and Sergej Proskurin and Marko Dorfhuber from Technical University of Munich

• CVE-2021-26311: Luca Wilke, Jan Wichelmann, Florian Sieck, and Thomas Eisenbarth from University of Lübeck 

Earlier this month, AMD dismissed the allegations that its CPUs were impacted by an attack that bypassed the patches for the original 2018 Spectre attack, detailed in a paper called “I see dead µops: leaking secrets via Intel/AMD micro-op caches”.

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