CVE-2021-3975Network attack vector

Daemon crash via unlocked monitor unregister

Published Aug 23, 2022 · Updated Aug 3, 2024

Use-after-free in libvirt before 7.1.0 allows remote authenticated users with read-only access to crash the libvirt daemon. In qemuProcessHandleMonitorEOF, concurrent threads can call qemuMonitorUnregister without the monitor lock, causing g_source_unref to release the same source more than once. A read-only connection and a guest shutting down are sufficient; successful exploitation terminates the management daemon and interrupts virtualization management.

CVSS severity6.5
Medium
EPSS probability1.54%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
Coverage for this vulnerability

See if you're affected

Explore vulnerability checks for your environment with Hinoki.

Book a demo

Summary

What happened

Use-after-free in libvirt before 7.1.0 allows remote authenticated users with read-only access to crash the libvirt daemon. In qemuProcessHandleMonitorEOF, concurrent threads can call qemuMonitorUnregister without the monitor lock, causing g_source_unref to release the same source more than once. A read-only connection and a guest shutting down are sufficient; successful exploitation terminates the management daemon and interrupts virtualization management.

The record

CVE
CVE-2021-3975
Published
Aug 23, 2022
Updated
Aug 3, 2024
Vendor
libvirt
Product
libvirt
Classifications
CWE-416, T1499.004
Attack vector
network
Privileges
authenticated

Timeline

How it unfolded

  1. Aug 23, 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

Compare your product and version with the public record. A matching version still requires validation against your environment.

Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=Fixed in libvirt v7.1.0

What conditions does exploitation require?

Attack vectornetwork
Required privilegesauthenticated

What is affected?

libvirt · libvirtversion=Fixed in libvirt v7.1.0

Published CVSS scores

6.5Red Hat, Inc.CVSS:3.1/AV:N/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.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-416Use After Free
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

See the directory against your own environment.

Your stack

Check the software in your environment

Book a demo to see how Hinoki identifies affected software and validates exploitability in your environment.

Book a demo