Google Cloud warns AMD Turin CPU side-channel flaws risk intra-VM data leaks requiring OS patch and reboot

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A vulnerabilidade

Three Transient Scheduler Attack (TSA) CPU side-channel flaws affect AMD Zen 5 (EPYC Turin) processors, which Google Cloud uses in C4D, N4D, H4D, Z4D and G4 VMs, including C4D and Z4D bare metal. The newest is CVE-2026-0004 (TSA-Fill in Xen's naming), which may let an attacker running code on the system infer data from the L1 data cache. CVE-2024-36350 (TSA-SQ) and CVE-2024-36357 (TSA-L1) were disclosed on July 8, 2025 for older EPYC chips, and AMD now says Zen 5 is affected too, correcting its earlier statement. AMD rates all three as local, high complexity, low privileges required. Inside a VM, an attacker with code on the same core may infer data from other processes or the kernel. Fixes need a patched guest kernel and a VM stop-start. Google rates the issue Medium.

Como funciona

The attacker must already be able to run code on the same processor core as the victim, for example in another process inside the same VM. The CPU's transient scheduling behavior lets some operations run speculatively before the processor has the data they depend on. The articles tie the flaws to the store queue (TSA-SQ) and the L1 data cache (TSA-L1 and TSA-Fill). Data from other processes or the kernel can influence what the attacker's code observes, so the attacker can infer it. The articles give no further detail on the mechanism.

Por que é vulnerável

The cause is a hardware weakness in how Zen 5 handles transient scheduling, which leaks data through side channels. AMD had earlier said Zen 5 was not vulnerable to TSA-SQ and TSA-L1; it now says Zen 5 is impacted differently from previously characterized processors. Mitigation needs several layers: CPU microcode and platform firmware, plus OS kernel code. A guest kernel can only enable its mitigations if the VM reports updated CPU information, which is why Google updates that information and requires a stop-start rather than a reboot. Mitigation may cost performance.

Como foi descoberta

The articles do not say who found CVE-2026-0004 or how. Google Cloud published a security bulletin this week, and AMD published a Zen 5 bulletin and a CVE-2026-0004 advisory. The Xen Project, which calls the new flaw TSA-Fill, published hypervisor patches and noted that AMD's earlier statement that Zen 5 was unaffected was corrected. TSA-SQ and TSA-L1 were first disclosed on July 8, 2025. None of the three is in CISA's KEV catalog, and neither company reports exploitation.

Explicação gerada por IA a partir da matéria e dos artigos, em 12/11/2026 11:15.