CVE-2021-46977

Host MSR corruption via preempted probe

Published Feb 28, 2024 · Updated Aug 5, 2026

A preemption race in affected Linux KVM VMX kernels allows local users to corrupt a host CPU user-return MSR during probing. The probe reads an MSR and later writes it back without disabling preemption, so migration between logical CPUs applies one CPU's saved value to another. Reachability requires local low-privileged access and KVM VMX activity; successful triggering corrupts host processor state and interrupts service.

CVSS severity7.8
High
EPSS probability0.24%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

A preemption race in affected Linux KVM VMX kernels allows local users to corrupt a host CPU user-return MSR during probing. The probe reads an MSR and later writes it back without disabling preemption, so migration between logical CPUs applies one CPU's saved value to another. Reachability requires local low-privileged access and KVM VMX activity; successful triggering corrupts host processor state and interrupts service.

The record

CVE
CVE-2021-46977
Published
Feb 28, 2024
Updated
Aug 5, 2026
Vendor
The Linux Kernel Organization
Product
Linux
Classifications
Unavailable
Attack vector
local
Privileges
authenticated

Timeline

How it unfolded

  1. Feb 28, 2024CVE publishedPublication date reported by the CVE source.
  2. Aug 5, 2026Record 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=4be5341026246870818e28b53202b001426a5aec <31f29749ee970c251b3a7e5b914108425940d089
  2. Affected versionversion=4be5341026246870818e28b53202b001426a5aec <5104d7ffcf24749939bea7fdb5378d186473f890
  3. Affected versionversion=4be5341026246870818e28b53202b001426a5aec <5adcdeb57007ccf8ab7ac20bf787ffb6fafb1a94
  4. Affected versionversion=4be5341026246870818e28b53202b001426a5aec <e3ea1895df719c4ef87862501bb10d95f4177bed
  5. Affected versionversion=5.5

What conditions does exploitation require?

Attack vectorlocal
Required privilegesauthenticated

What is affected?

The Linux Kernel Organization · Linuxversion=4be5341026246870818e28b53202b001426a5aec <31f29749ee970c251b3a7e5b914108425940d089; version=4be5341026246870818e28b53202b001426a5aec <5104d7ffcf24749939bea7fdb5378d186473f890; version=4be5341026246870818e28b53202b001426a5aec <5adcdeb57007ccf8ab7ac20bf787ffb6fafb1a94; version=4be5341026246870818e28b53202b001426a5aec <e3ea1895df719c4ef87862501bb10d95f4177bed; version=5.5

Published CVSS scores

7.8kernel.orgCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
5.5NIST NVDCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

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.

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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

No sourced classifications are available.

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

See the directory against your own environment.

Your stack

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