CVE-2021-4145

Guest-triggered host process crash via NULL dereference

Published Jan 25, 2022 · Updated Aug 3, 2024

NULL pointer dereference in QEMU before 6.2.0 allows guest OS users to crash the host QEMU process during block mirroring. mirror_iteration() passes a NULL self pointer to mirror_wait_on_conflicts(), which dereferences it when overlapping writes reach the mirrored node. An unprivileged guest must issue writes during an active block-mirror job; the resulting SIGSEGV interrupts that virtual machine and leaves leaked clusters in its disk image.

CVSS severity6.5
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 QEMU before 6.2.0 allows guest OS users to crash the host QEMU process during block mirroring. mirror_iteration() passes a NULL self pointer to mirror_wait_on_conflicts(), which dereferences it when overlapping writes reach the mirrored node. An unprivileged guest must issue writes during an active block-mirror job; the resulting SIGSEGV interrupts that virtual machine and leaves leaked clusters in its disk image.

The record

CVE
CVE-2021-4145
Published
Jan 25, 2022
Updated
Aug 3, 2024
Vendor
QEMU Project
Product
QEMU
Classifications
CWE-476, T1499.004
Attack vector
local
Privileges
authenticated

Timeline

How it unfolded

  1. Jan 25, 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=qemu-kvm 6.2.0

What conditions does exploitation require?

Attack vectorlocal
Required privilegesauthenticated

What is affected?

QEMU Project · QEMUversion=qemu-kvm 6.2.0

Published CVSS scores

4.9NIST NVDAV:L/AC:L/Au:N/C:N/I:N/A:C
6.5NIST NVDCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/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 9, 2026Sep 15, 2026
Latest reporting daySep 15, 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 Flaws

Public exploit references

No public exploit references are available in this record.

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Technologies

Your stack

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Your stack

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