CVE-2021-4147

Host service interruption via reentrant event deadlock

Published Mar 25, 2022 · Updated Aug 3, 2024

Improper locking in libvirt's libxl driver allows guest OS users to deadlock or crash the host's libvirtd daemon by rebooting. The event callback searches for and locks a virDomainObj while a shutdown thread already holds that object and calls into libxl, allowing a pending shutdown event to reenter the handler and wait on the same lock. Exploitation requires control of a guest on a Xen host using the libxl driver; repeated guest reboots can hang or crash libvirtd and interrupt host virtualization management.

CVSS severity6.5
Medium
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

Improper locking in libvirt's libxl driver allows guest OS users to deadlock or crash the host's libvirtd daemon by rebooting. The event callback searches for and locks a virDomainObj while a shutdown thread already holds that object and calls into libxl, allowing a pending shutdown event to reenter the handler and wait on the same lock. Exploitation requires control of a guest on a Xen host using the libxl driver; repeated guest reboots can hang or crash libvirtd and interrupt host virtualization management.

The record

CVE
CVE-2021-4147
Published
Mar 25, 2022
Updated
Aug 3, 2024
Vendor
libvirt
Product
libvirt
Classifications
CWE-667, T1499.004
Attack vector
local
Privileges
authenticated

Timeline

How it unfolded

  1. Mar 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=libvirt 2.33.0

What conditions does exploitation require?

Attack vectorlocal
Required privilegesauthenticated

What is affected?

libvirt · libvirtversion=libvirt 2.33.0

Published CVSS scores

6.5NIST NVDCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:N/I:N/A:H
7.1SUSECVSS:3.1/AV:L/AC:L/PR:N/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-667Improper Locking
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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