CVE-2021-4095

Host crash via null vCPU dereference

Published Mar 8, 2022 · Updated Aug 3, 2024

NULL pointer dereference in Linux Kernel KVM before 5.17-rc1 allows local users to crash the host via KVM_XEN_HVM_SET_ATTR. With dirty-ring logging enabled and no active vCPU, mark_page_dirty_in_slot calls kvm_dirty_ring_get, which dereferences a null vCPU pointer. Local access to the KVM device and the affected dirty-ring configuration are required; the resulting kernel oops interrupts host availability.

CVSS severity5.5
Medium
EPSS probability0.39%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

NULL pointer dereference in Linux Kernel KVM before 5.17-rc1 allows local users to crash the host via KVM_XEN_HVM_SET_ATTR. With dirty-ring logging enabled and no active vCPU, mark_page_dirty_in_slot calls kvm_dirty_ring_get, which dereferences a null vCPU pointer. Local access to the KVM device and the affected dirty-ring configuration are required; the resulting kernel oops interrupts host availability.

The record

CVE
CVE-2021-4095
Published
Mar 8, 2022
Updated
Aug 3, 2024
Vendor
The Linux Kernel Organization
Product
Linux Kernel
Classifications
CWE-476, T1499.004
Attack vector
local
Privileges
authenticated

Timeline

How it unfolded

  1. Mar 8, 2022CVE publishedPublication date reported by the CVE source.
  2. Aug 3, 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=Linux kernel versions prior to 5.17-rc1

What conditions does exploitation require?

Attack vectorlocal
Required privilegesauthenticated

What is affected?

The Linux Kernel Organization · Linux Kernelversion=Linux kernel versions prior to 5.17-rc1

Published CVSS scores

1.9NIST NVDAV:L/AC:M/Au:N/C:N/I:N/A:P
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

CWE-476NULL Pointer Dereference
T1499.004Application 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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