Public proof of conceptFix available

CVE-2021-3975

A public proof of concept exists; no exploitation attested.

Published2022-08-23
WeaknessCWE-416

Am I affected?

With a domain, we read the version its public headers and pages expose. A distribution build can carry the fix under an older number.

Description

A use-after-free flaw was found in libvirt. The qemuMonitorUnregister() function in qemuProcessHandleMonitorEOF is called using multiple threads without being adequately protected by a monitor lock. This flaw could be triggered by the virConnectGetAllDomainStats API when the guest is shutting down. An unprivileged client with a read-only connection could use this flaw to perform a denial of service attack by causing the libvirt daemon to crash.

Timeline

dates in UTC

2022-08-2320:15CVE publishedNVD
2026-10-2319:23First public proof of conceptPoC-in-GitHub

Observed activity

isMalicious corpus · updated 2026-10-23 21:37 UTC

Indicators tagged with this CVE, per day0 indicators over 7 days

Block these indicators

Firewall list (EDL, text): https://api.ismalicious.com/edl/cve/CVE-2021-3975?format=txt
CSV export: https://api.ismalicious.com/edl/cve/CVE-2021-3975?format=csv
TAXII collection of exploited CVEs
The EDL and CSV take an API key on the Pro plan.

Versions per branch

NVD

Debian debian linux

Branch	Affected	Fixed in	Source
10.0	= 10.0	no fix published	NVD
11.0	= 11.0	no fix published	NVD

Canonical ubuntu linux

Branch	Affected	Fixed in	Source
21.10	= 21.10	no fix published	NVD

Fedoraproject fedora

Branch	Affected	Fixed in	Source
35.x	= 35	no fix published	NVD

11 more products in the sources.

as publishedRanges as NVD and OSV publish them; a distribution’s build can be fixed under an older number.

Distribution builds and vendor advisories

Packages from OSV.dev and products from the vendors' CSAF advisories.

version not verifiedVersions not verified: read as OSV.dev and the vendors publish them, not checked against each vendor's release list.

Packages

hivexAlmaLinux:8all versions · fixed in 1.3.18-23.module_el8.6.0+2880+7d9e3703and 6 other packages
libguestfsAlmaLinux:8all versions · fixed in 1:1.44.0-5.module_el8.6.0+2880+7d9e3703.almaand 24 other packages
libguestfs-winsupportAlmaLinux:8all versions · fixed in 8.6-1.module_el8.6.0+2880+7d9e3703
libiscsiAlmaLinux:8all versions · fixed in 1.18.0-8.module_el8.6.0+2880+7d9e3703and 2 other packages
libnbdAlmaLinux:8all versions · fixed in 1.6.0-5.module_el8.6.0+2880+7d9e3703and 6 other packages
libtpmsAlmaLinux:8all versions · fixed in 0.9.1-0.20211126git1ff6fe1f43.module_el8.6.0+2880+7d9e3703and 1 other package
libvirtAlmaLinux:8all versions · fixed in 8.0.0-5.module_el8.6.0+2880+7d9e3703and 27 other packages
libvirt-dbusAlmaLinux:8all versions · fixed in 1.3.0-2.module_el8.6.0+2880+7d9e3703

10 more package ranges on OSV.dev

Full record on NVD

Fix

Advisories and patches

Detection

read 2026-10-23 19:23 UTC

Nuclei template: none so far
Exploit-DB: no entry
Proof-of-concept repositories: 1 repository, unverifiedyan5ui/ENV-CVE-2021-3975

Sources

NVDCVSS 3.16.5read 2026-10-23
CNAweakness (CWE)CWE-416read 2026-10-23
NVDweakness (CWE)CWE-416read 2026-10-23
FIRST EPSSEPSS score1.6 %2026-10-23
PoC-in-GitHubproof of concept1read 2026-10-23
OSVaffected packages—

Technical details

CVSS v3 Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
Published: 2022-08-23
Last Modified: 2026-06-17
NVD status: Modified

Frequently asked questions

What is CVE-2021-3975?

Is CVE-2021-3975 actively exploited?

Active exploitation of CVE-2021-3975 has not been confirmed. Its EPSS score was 1.6% on 2026-10-23, the estimated probability of exploitation in the next 30 days.

What is the CVSS score for CVE-2021-3975?

CVE-2021-3975 has a CVSS v3 base score of 6.5 (MEDIUM severity), with vector string CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H.

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