CVE-2021-4158Public exploit

Host process crash via unchecked hotplug bus lookup

Published Aug 24, 2022 · Updated Aug 3, 2024

NULL pointer dereference in QEMU ACPI PCI hotplug code allows privileged guest OS users to crash the host process through port I/O. In hw/acpi/pcihp.c, pci_write uses a guest-controlled hotplug selector to find a PCI bus, then traverses the bus without checking whether the lookup returned NULL. Access requires control of a privileged guest workload, and the demonstrated consequence is termination of that guest's host QEMU process.

CVSS severity6.0
Medium
EPSS probability0.40%
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 ACPI PCI hotplug code allows privileged guest OS users to crash the host process through port I/O. In hw/acpi/pcihp.c, pci_write uses a guest-controlled hotplug selector to find a PCI bus, then traverses the bus without checking whether the lookup returned NULL. Access requires control of a privileged guest workload, and the demonstrated consequence is termination of that guest's host QEMU process.

The record

CVE
CVE-2021-4158
Published
Aug 24, 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. Aug 24, 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=Affects v6.0.0 and above.

What conditions does exploitation require?

Attack vectorlocal
Required privilegesauthenticated

What is affected?

QEMU Project · QEMUversion=Affects v6.0.0 and above.

Published CVSS scores

6.0Red HatCVSS:3.1/AV:L/AC:L/PR:H/UI:N/S:C/C:N/I:N/A:H
6.0NIST NVDCVSS:3.1/AV:L/AC:L/PR:H/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 exploitPublished

Weakness, pattern, technique

CWE-476NULL Pointer Dereference
T1499.004Application or System Exploitation

Public exploit references

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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