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Epyc 7001 FirmwareOperating system · Amd

CVE-2021-26340

HIGH · 8.4 CVSS v3.1 Published 2021-12-10
Mitigation only
No fix yet — a mitigation exists. There is no fixed release. A documented workaround reduces exposure in the meantime.
See remediation →
86/100
Remediation priority · High
Zero-click

Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.

NVD · unedited
A malicious hypervisor in conjunction with an unprivileged attacker process inside an SEV/SEV-ES guest VM may fail to flush the Translation Lookaside Buffer (TLB) resulting in unexpected behavior inside the virtual machine (VM).

Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.

dbcve analysis · moderate confidence

This vulnerability in AMD SEV/SEV-ES virtualization technology allows a malicious hypervisor combined with an unprivileged attacker process inside the guest VM to cause TLB (Translation Lookaside Buffer) flush failures, potentially leading to memory corruption or information disclosure within the protected VM.

MitigationEnsure hypervisor and guest VM configurations follow AMD's security guidelines for SEV/SEV-ES; apply any available AMD processor microcode and hypervisor updates that address TLB management in encrypted VMs.

Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.

Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.

NVD · CPE data
Epyc 7001 FirmwareOperating system
Affected:all versions
Epyc 7232p FirmwareOperating system
Affected:all versions
Epyc 7251 FirmwareOperating system
Affected:all versions
Epyc 7261 FirmwareOperating system
Affected:all versions
Epyc 7252 FirmwareOperating system
Affected:all versions
Epyc 74f3 FirmwareOperating system
Affected:all versions
Epyc 7501 FirmwareOperating system
Affected:all versions
Epyc 7502 FirmwareOperating system
Affected:all versions

CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.

From the vector
Attack vector
Local
Complexity
Low
Privileges
Low
User interaction
None
Scope
Changed
Confidentiality
High
Integrity
High
Availability
None

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:N

Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.

dbcve checks

Work through these to decide whether this CVE applies to you.

  1. Identify the AMD Epyc processor model
    Run 'cat /proc/cpuinfo' or 'lscpu' and look for the 'model name' field. Confirm it matches one of the affected models: Epyc 7001, 7232p, 7251, 7261, 7252, 74f3, 7501, or 7502.
    Affected if The processor is an AMD Epyc 7001, 7232p, 7251, 7261, 7252, 74f3, 7501, or 7502.
  2. Verify SEV/SEV-ES support is present
    Check /proc/cpuinfo for 'pdpe1gb' flag (required for SEV) and run 'kvmstat --event hyperv.tlbflush' or check hypervisor documentation to see if SEV/SEV-ES is exposed to virtual machines.
    Affected if SEV or SEV-ES is enabled and the hypervisor exposes encrypted memory support to guest VMs.
  3. Confirm the hypervisor is configured for SEV/SEV-ES
    For QEMU/KVM, check the VM XML config with 'virsh dumpxml <vm_name>' and look for '<sev>' or '<memory encryption>' elements. For other hypervisors, review the VM configuration for SEV/SEV-ES encryption settings.
    Affected if The VM configuration explicitly enables SEV or SEV-ES (memory encryption is active).
  4. Check the PSP firmware version
    On the host, run 'dmidecode' or check the hypervisor logs for PSP (Platform Security Processor) firmware version. On AMD systems, 'cat /sys/firmware/efi/fw_platform_size' or vendor-specific tools may expose this.
    Affected if The PSP firmware version is any version on the listed affected processors, since all firmware versions are impacted.
  5. Determine if guest VM is running with encrypted memory
    Inside the guest VM, check if memory is reported as encrypted. On Linux guests, run 'cat /proc/keys' or check 'dmesg' for SEV-related messages. On Windows, check Task Manager or 'msinfo32' for memory encryption status.
    Affected if The guest VM reports encrypted memory or SEV/SEV-ES is actively protecting the VM.

A system is affected if it uses an AMD Epyc 7001, 7232p, 7251, 7261, 7252, 74f3, 7501, or 7502 processor with SEV/SEV-ES enabled and the hypervisor exposes encrypted memory to a guest VM.

Generated from the published advisory. Verify against your own configuration.

Check your environment

Paste your version and any relevant configuration and it will be compared against the affected criteria above. Do not include secrets or credentials.

AI-assisted, checked against the advisory. Informational, not a guarantee.

Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.

From vendor data
Mitigation available No clean upgrade yet — mitigate in the meantime
Mitigation

Ensure hypervisor and guest VM configurations follow AMD's security guidelines for SEV/SEV-ES; apply any available AMD processor microcode and hypervisor updates that address TLB management in encrypted VMs.

Fix this in Epyc 7001 Firmware Scoped from the published advisory
  • Consultation4.0 h
  • Implementation8.0 h
  • Testing6.0 h
  • Review / QA4.0 h
22.0 hours of engineering $3,860
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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2021-26340 in production — separate from our analysis above.

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What this is

A place for practitioners to share what actually worked: a mitigation you’ve tested, a configuration change, a version- or environment-specific caveat, or a link to a verified patch. The most useful notes rise to the top as peers upvote them, so the signal stays high.

What belongs here
  • Verified mitigations, workarounds, and config changes
  • Version or environment caveats, and links to real fixes
  • No weaponised exploit code, or anything meant to cause harm
  • No spam, self-promotion, credentials, or personal data