CVE-2021-26339

Guest-triggered CPU core hang via crafted instructions

Published May 11, 2022 · Updated Sep 17, 2024

Denial of service in AMD EPYC, Athlon, and Ryzen processors allows guest OS users to hang a CPU core from an unprivileged VM. The processor core mishandles a specific hand-crafted x86 instruction sequence that ordinary compilers do not generate, leaving the core hung. Execution inside an unprivileged guest VM is required; the demonstrated consequence is a single-core hang, with no reported data disclosure or modification.

CVSS severity5.5
Medium
EPSS probability0.27%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Denial of service in AMD EPYC, Athlon, and Ryzen processors allows guest OS users to hang a CPU core from an unprivileged VM. The processor core mishandles a specific hand-crafted x86 instruction sequence that ordinary compilers do not generate, leaving the core hung. Execution inside an unprivileged guest VM is required; the demonstrated consequence is a single-core hang, with no reported data disclosure or modification.

The record

CVE
CVE-2021-26339
Published
May 11, 2022
Updated
Sep 17, 2024
Vendor
AMD
Product
AMD EPYC Processors
Classifications
CWE-1281, CAPEC-212, T1499.004
Attack vector
local
Privileges
authenticated

Timeline

How it unfolded

  1. May 11, 2022CVE publishedPublication date reported by the CVE source.
  2. Sep 17, 2024Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=various

What conditions does exploitation require?

Attack vectorlocal
Required privilegesauthenticated

What is affected?

AMD · AMD EPYC Processorsversion=various
AMD · AMD Athlon Processorsversion=various
AMD · AMD Ryzen Processorsversion=various

Published CVSS scores

5.5NIST NVDCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
4.9NIST NVDAV:L/AC:L/Au:N/C:N/I:N/A:C

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectorlocal
Privilegesauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-1281Sequence of Processor Instructions Leads to Unexpected Behavior
CAPEC-212Functionality Misuse
T1499.004Endpoint Denial of Service: Application or System Exploitation

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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