CVE-2021-3975

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.

Published: 2022-08-23 Last update: 2026-06-17 Assigner: [email protected] Source: [email protected]
NVD Status：Modified，CVE State: published
View at NVD, CVE.org, EUVD

CVE-2021-3975 is rated Moderate Risk (48.7/100): CVSS Medium severity, with medium exploitation likelihood (EPSS 1.17%). Review affected assets and schedule remediation.

Risk is dynamic; we continuously reassess and refresh what is shown on this page as upstream context changes.

Exploit prediction scoring system (EPSS) score for CVE-2021-3975

EPSS lead: Daily EPSS estimates relative likelihood of exploitation; percentile ranks this CVE among scored vulnerabilities (higher = more severe relative rank).

# Date Old EPSS score New EPSS score Delta (New - Old)
1 2026-06-15 0.61% 1.17% +0.56%
2 2026-05-29 0.46% 0.61% +0.16%
3 2026-01-30 — 0.46% —

Full EPSS history (17 records total)

Common vulnerability scoring system (CVSS) metrics for CVE-2021-3975

CVSS metrics for this CVE.

Base score Version Severity Vector Exploitability Impact Score source
6.5 3.1 MEDIUM
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H Click to expand
Attack vector (AV:N)
Could be attacked over the internet or any normal routed network—not just someone sitting at the machine.
Attack complexity (AC:L)
Once they can reach the bug, pulling it off is straightforward—no weird race conditions or rare setup.
Privileges required (PR:L)
A normal user session is enough; they don’t have to be admin.
User interaction (UI:N)
Nobody has to click “OK” or open a trap file; it can work without a victim helping.
Scope (S:U)
Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems.
Confidentiality (C:N)
Doesn’t really leak secrets in a meaningful way.
Integrity (I:N)
Data isn’t meaningfully altered or forged.
Availability (A:H)
Could take the service down hard or make it unusable for people who depend on it.
 2.8 3.6 [email protected]

Weakness enumeration for CVE-2021-3975

OS Trackers for CVE-2021-3975

vendor priority summary link
alpine — CVE-2021-3975: 1 source package rows (libvirt); 6 state rows across 2 repos (3.22-community, edge-community); fixed 0, open 6. https://security.alpinelinux.org/vuln/CVE-2021-3975
debian not yet assigned CVE-2021-3975 not yet assigned priority: Debian including 1 source packages (libvirt), 5 status rows across 5 suites (bookworm, bullseye, forky, sid, trixie): resolved 5. https://security-tracker.debian.org/tracker/CVE-2021-3975
redhat low — https://access.redhat.com/security/cve/CVE-2021-3975
suse medium CVE-2021-3975 severity moderate: SUSE including 452 source package names (amazon/suse-sles-15-sp1-chost-byos-v20210304-hvm-ssd-x86_64, amazon/suse-sles-15-sp1-chost-byos-v20220127-hvm-ssd-x86_64, …), 1841 product×package rows across 72 product lines (HPE Helion OpenStack 8, Image SLES12-SP5-Azure-SAP-BYOS, … (72 product lines)): Fixed 1184, Known Not Affected 426, Known Affected 231. https://www.suse.com/security/cve/CVE-2021-3975/
ubuntu low CVE-2021-3975 low priority: Ubuntu including 1 source packages (libvirt), 15 status rows across 15 suites (bionic, focal, hirsute, impish, jammy, kinetic, lunar, mantic, noble, oracular, plucky, questing, trusty, upstream, xenial): released 11, needs-triage 2, ignored 1, not-affected 1. https://ubuntu.com/security/CVE-2021-3975

Affected software / configurations for CVE-2021-3975

Vendor Product Version Raw CPE
redhat libvirt < 7.1.0 cpe:2.3:a:redhat:libvirt:*:*:*:*:*:*:*:*
canonical ubuntu_linux 21.10 cpe:2.3:o:canonical:ubuntu_linux:21.10:*:*:*:*:*:*:*
fedoraproject fedora 35 cpe:2.3:o:fedoraproject:fedora:35:*:*:*:*:*:*:*
redhat enterprise_linux 8.0 cpe:2.3:o:redhat:enterprise_linux:8.0:*:*:*:*:*:*:*
redhat enterprise_linux_eus 8.6 cpe:2.3:o:redhat:enterprise_linux_eus:8.6:*:*:*:*:*:*:*
redhat enterprise_linux_for_ibm_z_systems 8.0 cpe:2.3:o:redhat:enterprise_linux_for_ibm_z_systems:8.0:*:*:*:*:*:*:*
redhat enterprise_linux_for_ibm_z_systems_eus 8.6 cpe:2.3:o:redhat:enterprise_linux_for_ibm_z_systems_eus:8.6:*:*:*:*:*:*:*
redhat enterprise_linux_for_power_little_endian 8.0 cpe:2.3:o:redhat:enterprise_linux_for_power_little_endian:8.0:*:*:*:*:*:*:*
redhat enterprise_linux_for_power_little_endian_eus 8.6 cpe:2.3:o:redhat:enterprise_linux_for_power_little_endian_eus:8.6:*:*:*:*:*:*:*
redhat enterprise_linux_server_for_power_little_endian_update_services_for_sap_solutions 8.6 cpe:2.3:o:redhat:enterprise_linux_server_for_power_little_endian_update_services_for_sap_solutions:8.6:*:*:*:*:*:*:*
redhat enterprise_linux_server_tus 8.6 cpe:2.3:o:redhat:enterprise_linux_server_tus:8.6:*:*:*:*:*:*:*
redhat codeready_linux_builder — cpe:2.3:a:redhat:codeready_linux_builder:-:*:*:*:*:*:*:*
debian debian_linux 10.0 cpe:2.3:o:debian:debian_linux:10.0:*:*:*:*:*:*:*
debian debian_linux 11.0 cpe:2.3:o:debian:debian_linux:11.0:*:*:*:*:*:*:*
netapp ontap_select_deploy_administration_utility — cpe:2.3:a:netapp:ontap_select_deploy_administration_utility:-:*:*:*:*:*:*:*

References for CVE-2021-3975

cvelogic Threat Intelligence