CVE-2021-26401
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 · uneditedLFENCE/JMP (mitigation V2-2) may not sufficiently mitigate CVE-2017-5715 on some AMD CPUs.
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 confidenceThis CVE addresses a failure of the LFENCE/JMP mitigation (V2-2) for Spectre Variant 2 (CVE-2017-5715) on certain AMD processors. The hardware-level mitigation may not properly prevent speculative execution attacks on some AMD CPU models, potentially allowing attackers to leak sensitive information via branch target injection.
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 dataall versionsall versionsall versionsall versionsall versionsall versionsall versionsall versionsCVSS 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
- High
- Privileges
- Low
- User interaction
- None
- Scope
- Changed
- Confidentiality
- High
- Integrity
- None
- Availability
- None
CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:C/C:H/I:N/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 checksWork through these to decide whether this CVE applies to you.
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Identify CPU modelRun command 'wmic cpu get Name' on Windows or 'cat /proc/cpuinfo' on Linux to identify the processor. Look for 'Athlon X4' followed by 940, 950, 970, 835, 845, 830, 840, or 860k.Affected if The CPU is an AMD Athlon X4 940, 950, 970, 835, 845, 830, 840, or 860k model.
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Check BIOS versionRun 'wmic bios get SMBIOSBIOSVersion' on Windows or check BIOS/UEFI settings directly. Consult system vendor documentation for the expected version.Affected if The BIOS is outdated and does not contain the AMD microcode update for CVE-2021-26401.
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Check microcode versionOn Linux, run 'dmesg | grep -i microcode' or check '/proc/cpuinfo' for microcode version. On Windows, use 'wmic cpu get version' or CPU-Z tool.Affected if The loaded microcode version predates the fix for CVE-2021-26401 or shows as '0x' (unpatched).
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Verify mitigation statusOn Linux, check /sys/devices/system/cpu/vulnerabilities/spectre_v2 (cat /sys/devices/system/cpu/vulnerabilities/spectre_v2). It should show 'Mitigation: Full AMD retpoline, light weight IBRS+'. Pure 'LFENCE/JMP' without retpoline may indicate the bypass is possible.Affected if The mitigation shows only 'LFENCE/JMP' without retpoline or 'IBRS+' on an affected CPU, indicating potential susceptibility.
A user is affected if their system uses an AMD Athlon X4 940/950/970/835/845/830/840/860k processor with outdated BIOS/firmware that lacks the CVE-2021-26401 microcode fix, and the spectre_v2 mitigation shows only LFENCE/JMP without additional protections.
Generated from the published advisory. Verify against your own configuration.
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 dataApply AMD-provided firmware/microcode updates and BIOS updates as they become available. For affected systems where patches are unavailable, consider CPU replacement with newer unaffected processors.
- Consultation8.0 h
- Implementation24.0 h
- Testing16.0 h
- Review / QA8.0 h
An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $15,616.
Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2021-26401 — or any other known-vulnerable package — straight from your lock files. Free and open source; it runs locally and uploads nothing.
References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.
Primary sourcesPractitioner notes
ContributedPeer-ranked notes from engineers who’ve handled CVE-2021-26401 in production — separate from our analysis above.
The advisory tells you what broke. It rarely tells you what actually worked. If you’ve dealt with this one, that detail is what the next engineer is searching for.
- The version that genuinely resolved it — not the one the vendor claimed
- A config change or rule that shut the vector down
- A gotcha in the upgrade path that cost you an afternoon
No notes yet
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- 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
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