NVD / CVE Program· CNA redhat

CVE-2021-3975: A use-after-free flaw was found in libvirt.

Noroxi assessment

Priority: Monitor (action score 26/100)

Public proof-of-concept code exists (GitHub); there is no record of exploitation in the wild.
Probability of exploitation in the next 30 days: 1.6% (FIRST EPSS); higher than 76.4% of all records.
Anyone who can reach it over the internet can trigger it. A low-privileged account is enough. No user action is required. No special conditions are required; it is repeatable.
Fixed version: libvirt (Debian:10) 5.0.0-4+deb10u2; libvirt (Debian:12) 7.6.0-1; hivex (Red Hat:advanced_virtualization:8.5::el8) 0:1.3.18-22.module+el8.5.0+12087+2208d04c.

Low priority for now. Upgrade to libvirt (Debian:10) 5.0.0-4+deb10u2; libvirt (Debian:12) 7.6.0-1; hivex (Red Hat:advanced_virtualization:8.5::el8) 0:1.3.18-22.module+el8.5.0+12087+2208d04c or later.

Generated automatically from the record's data: CVSS (NVD and CNA), CISA KEV and SSVC, FIRST EPSS, exploit sources, fixed versions. How we calculate it

Primary sources: NVD · CVE.org · FIRST EPSS

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.

MediumCVSS 6.5 · v3.1—Proof of concept Fix available

Published: Aug 23, 2022
Updated: Jun 17, 2026
EPSS: 1.6% · 76th percentile
CWE: CWE-416

Report tools

JSON

Action score

Monitor

Low priority for now.

CVSS: 26 / 40 · 6.5 / 10
CISA KEV: 0 / 30 · Not listed
EPSS: 0 / 30 · 1.6%

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Not in KEV: no record of exploitation in the wild
Proof of concept exists, no weaponized module
A fix has been released

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Noroxi analysis

What does it mean in your environment?

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Affected systems

Is your version affected?

Pick the product and type the version you run. It's compared with this record's version ranges in your browser; the version isn't sent anywhere.

Vendor	Product	CPE
redhat	libvirt	cpe:2.3:a:redhat:libvirt
redhat	enterprise linux	cpe:2.3:o:redhat:enterprise_linux
redhat	enterprise linux eus	cpe:2.3:o:redhat:enterprise_linux_eus
redhat	enterprise linux for ibm z systems	cpe:2.3:o:redhat:enterprise_linux_for_ibm_z_systems
redhat	enterprise linux for ibm z systems eus	cpe:2.3:o:redhat:enterprise_linux_for_ibm_z_systems_eus
redhat	enterprise linux for power little endian	cpe:2.3:o:redhat:enterprise_linux_for_power_little_endian
redhat	enterprise linux for power little endian eus	cpe:2.3:o:redhat:enterprise_linux_for_power_little_endian_eus
redhat	enterprise linux server for power little endian update services for sap solutions	cpe:2.3:o:redhat:enterprise_linux_server_for_power_little_endian_update_services_for_sap_solutions
redhat	enterprise linux server tus	cpe:2.3:o:redhat:enterprise_linux_server_tus
redhat	codeready linux builder	cpe:2.3:a:redhat:codeready_linux_builder
canonical	ubuntu linux	cpe:2.3:o:canonical:ubuntu_linux
fedoraproject	fedora	cpe:2.3:o:fedoraproject:fedora

and 2 more

Affected versions

NVD version ranges (for catalog products). Add the product to your stack with a version and matching uses these.

canonical ubuntu linux21.10
debian debian linux10.0
debian debian linux11.0
fedoraproject fedora35
netapp ontap select deploy administration utilityall versions
redhat codeready linux builderall versions
redhat enterprise linux8.0
redhat enterprise linux eus8.6
redhat enterprise linux for ibm z systems8.0
redhat enterprise linux for ibm z systems eus8.6
redhat enterprise linux for power little endian8.0
redhat enterprise linux for power little endian eus8.6
redhat enterprise linux server for power little endian update services for sap solutions8.6
redhat enterprise linux server tus8.6
redhat libvirtbefore 7.1.0

Versions reported by the vendor

Affected version ranges reported by the assigning authority (redhat). Independent of NVD's CPE analysis and usually ahead of it.

n/a libvirt
- Fixed in libvirt v7.1.0affected

Package-level exposure

OSV and GitHub Advisory data: ecosystem, package and range. SBOM matching uses this table.

+96

Same product

redhat: all records

Other highest-scoring records for the same primary product.

CVE-2016-5008libvirt before 2.0.0 improperly disables password checking when the password on a VNC server is set to an empty string, which allows remote
40Plan
CVE-2020-14339A flaw was found in libvirt, where it leaked a file descriptor for `/dev/mapper/control` into the QEMU process.
35Monitor
CVE-2019-10132A vulnerability was found in libvirt >= 4.1.0 in the virtlockd-admin.socket and virtlogd-admin.socket systemd units.
35Monitor

Published before and after this one in the same product

← EarlierCVE-2021-4147Mar 25, 2022 · A flaw was found in the libvirt libxl driver.
26Monitor
← EarlierCVE-2022-0897Mar 25, 2022 · A flaw was found in the libvirt nwfilter driver.
17Monitor
Later →CVE-2023-2700May 15, 2023 · A vulnerability was found in libvirt.
22Monitor

Remediation

Which version to upgrade to

Fix versions compiled from the vendor, package registries and Microsoft. Verify the vendor's note before upgrading.

Product / package	Fixed version	Source
debian:libvirt	7.6.0-1 · Debian:12	Package registry (OSV)
red hat:hivex	0:1.3.18-22.module+el8.5.0+12087+2208d04c · Red Hat:advanced_virtualization:8.5::el8	Package registry (OSV)
red hat:hivex-debuginfo	0:1.3.18-22.module+el8.5.0+12087+2208d04c · Red Hat:advanced_virtualization:8.5::el8	Package registry (OSV)
red hat:hivex-debugsource	0:1.3.18-22.module+el8.5.0+12087+2208d04c · Red Hat:advanced_virtualization:8.5::el8	Package registry (OSV)
red hat:hivex-devel	0:1.3.18-22.module+el8.5.0+12087+2208d04c · Red Hat:advanced_virtualization:8.5::el8	Package registry (OSV)
red hat:libguestfs	1:1.44.0-3.module+el8.5.0+10681+17a9b157 · Red Hat:advanced_virtualization:8.5::el8	Package registry (OSV)
red hat:libguestfs-bash-completion	1:1.44.0-3.module+el8.5.0+10681+17a9b157 · Red Hat:advanced_virtualization:8.5::el8	Package registry (OSV)
red hat:libguestfs-debuginfo	1:1.44.0-3.module+el8.5.0+10681+17a9b157 · Red Hat:advanced_virtualization:8.5::el8	Package registry (OSV)
red hat:libguestfs-debugsource	1:1.44.0-3.module+el8.5.0+10681+17a9b157 · Red Hat:advanced_virtualization:8.5::el8	Package registry (OSV)
red hat:libguestfs-devel	1:1.44.0-3.module+el8.5.0+10681+17a9b157 · Red Hat:advanced_virtualization:8.5::el8	Package registry (OSV)
red hat:libguestfs-gfs2	1:1.44.0-3.module+el8.5.0+10681+17a9b157 · Red Hat:advanced_virtualization:8.5::el8	Package registry (OSV)
red hat:libguestfs-gobject	1:1.44.0-3.module+el8.5.0+10681+17a9b157 · Red Hat:advanced_virtualization:8.5::el8	Package registry (OSV)
red hat:SLOF	0:20210217-1.module+el8.5.0+10946+35bb3930 · Red Hat:advanced_virtualization:8.5::el8	Package registry (OSV)
suse:libvirt	4.0.0-9.40.1 · SUSE:Linux Enterprise High Performance Computing 15-ESPOS	Package registry (OSV)

Exploit status

Proof of concept available

A public proof of concept or detection signature exists. Exploit knowledge is out there; don't delay patching.

Evidence

Proof-of-concept repository on GitHub ×1

Noroxi does not host or link to exploit code. Metasploit module names and Nuclei template ids are shown (names, not code); Exploit-DB entries and PoC repositories are given as counts only.

Public exploit evidence
Source	Kind	Date
Proof-of-concept repository on GitHub	stars:0	2026-06-17

Research context

For pentesters and researchers: attack profile, score disagreement, timeline, patch commits, credits, variant and chain candidates, bug bounty scope. All derived from existing data; no exploit code.

Timeline

From publication to today: proof of concept, Metasploit module, CISA KEV and fix record. Dates are as reported by the sources.

PublishedAug 23, 2022
First PoCJun 17, 2026+1393 d
TodayNov 4, 2026+1533 d

No history yet (it accumulates with the daily EPSS job).

Patch and commit links

Commit, PR and diff links among the references. A starting point for patch-diffing and variant hunting; fixes, not exploits.

libvirt/libvirtcommit 1ac703a

Credits

All researchers

Finders, reporters and analysts named in the CNA record. Click a name for that researcher’s other records.

No credits in the CNA record.

Variant candidates

Same product, same weakness class, within 18 months. If the patch missed the root cause, the sibling bug is here.

No nightly-computed relations.

Chain candidates

An authentication bypass and a privilege-requiring bug in the same product, published close together: combined they may become an unauthenticated path.

—

Bug bounty scope

No known public program.

Source: bounty-targets-data (public HackerOne, Bugcrowd, Intigriti, YesWeHack listings).

Technical details

Attack conditions

Anyone who can reach it over the internet can trigger it.
A low-privileged account is enough.
No user action is required.
No special conditions are required; it is repeatable.

If successful

Confidentiality: none
Integrity: none
Availability: high · the service can be disrupted

Attack vector: Network
Attack complexity: Low
Privileges required: Low
User interaction: None
Scope: Unchanged
Confidentiality impact: None
Integrity impact: None
Availability impact: High

Weakness class (CWE)

CWE-416 · Use After Free

CVSS vector

CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

nvd-primary

Root cause

After a memory region is freed, another reference pointing to it is still used. By then, the same region may have been allocated for different data.

The bug in code

The whole CWE-416 class

A representative example of this vulnerability class. Not the vendor's source code; it shows the faulty pattern and its fix.

Vulnerable

1free(dev->buf);
2/* ... another thread is still running ... */
3process(dev->buf);

Fixed

1lock(&dev->lock);
2free(dev->buf);
3dev->buf = NULL;
4unlock(&dev->lock);

Attack context

MITRE CAPEC attack patterns and ATT&CK techniques for this weakness class (CWE). A starting point for detection rules and threat hunting.

MITRE has no CAPEC/ATT&CK mapping for this CWE.

Change log

Fix✗ → ✓Sep 28, 2026, 10:46 PM UTC

For records you follow, these changes also arrive as notifications. →

References

access.redhat.com/security/cve/CVE-2021-3975

Show all references (5 more)

Vendor advisories and official records. Exploit/PoC links are deliberately left out.

All records

Ecosystem	Package	Affected range	Fix
Debian:10	libvirt	before 5.0.0-4+deb10u2	5.0.0-4+deb10u2
Debian:12	libvirt	before 7.6.0-1	7.6.0-1
Red Hat:advanced_virtualization:8.5::el8	hivex	before 0:1.3.18-22.module+el8.5.0+12087+2208d04c	0:1.3.18-22.module+el8.5.0+12087+2208d04c
Red Hat:advanced_virtualization:8.5::el8	hivex-debuginfo	before 0:1.3.18-22.module+el8.5.0+12087+2208d04c	0:1.3.18-22.module+el8.5.0+12087+2208d04c
Red Hat:advanced_virtualization:8.5::el8	hivex-debugsource	before 0:1.3.18-22.module+el8.5.0+12087+2208d04c	0:1.3.18-22.module+el8.5.0+12087+2208d04c
Red Hat:advanced_virtualization:8.5::el8	hivex-devel	before 0:1.3.18-22.module+el8.5.0+12087+2208d04c	0:1.3.18-22.module+el8.5.0+12087+2208d04c
Red Hat:advanced_virtualization:8.5::el8	libguestfs	before 1:1.44.0-3.module+el8.5.0+10681+17a9b157	1:1.44.0-3.module+el8.5.0+10681+17a9b157
Red Hat:advanced_virtualization:8.5::el8	libguestfs-bash-completion	before 1:1.44.0-3.module+el8.5.0+10681+17a9b157	1:1.44.0-3.module+el8.5.0+10681+17a9b157
Red Hat:advanced_virtualization:8.5::el8	libguestfs-debuginfo	before 1:1.44.0-3.module+el8.5.0+10681+17a9b157	1:1.44.0-3.module+el8.5.0+10681+17a9b157
Red Hat:advanced_virtualization:8.5::el8	libguestfs-debugsource	before 1:1.44.0-3.module+el8.5.0+10681+17a9b157	1:1.44.0-3.module+el8.5.0+10681+17a9b157
Red Hat:advanced_virtualization:8.5::el8	libguestfs-devel	before 1:1.44.0-3.module+el8.5.0+10681+17a9b157	1:1.44.0-3.module+el8.5.0+10681+17a9b157
Red Hat:advanced_virtualization:8.5::el8	libguestfs-gfs2	before 1:1.44.0-3.module+el8.5.0+10681+17a9b157	1:1.44.0-3.module+el8.5.0+10681+17a9b157
Red Hat:advanced_virtualization:8.5::el8	libguestfs-gobject	before 1:1.44.0-3.module+el8.5.0+10681+17a9b157	1:1.44.0-3.module+el8.5.0+10681+17a9b157
Red Hat:advanced_virtualization:8.5::el8	libguestfs-gobject-debuginfo	before 1:1.44.0-3.module+el8.5.0+10681+17a9b157	1:1.44.0-3.module+el8.5.0+10681+17a9b157
Red Hat:advanced_virtualization:8.5::el8	libguestfs-gobject-devel	before 1:1.44.0-3.module+el8.5.0+10681+17a9b157	1:1.44.0-3.module+el8.5.0+10681+17a9b157
Red Hat:advanced_virtualization:8.5::el8	libguestfs-inspect-icons	before 1:1.44.0-3.module+el8.5.0+10681+17a9b157	1:1.44.0-3.module+el8.5.0+10681+17a9b157
Red Hat:advanced_virtualization:8.5::el8	libguestfs-java	before 1:1.44.0-3.module+el8.5.0+10681+17a9b157	1:1.44.0-3.module+el8.5.0+10681+17a9b157
Red Hat:advanced_virtualization:8.5::el8	libguestfs-java-debuginfo	before 1:1.44.0-3.module+el8.5.0+10681+17a9b157	1:1.44.0-3.module+el8.5.0+10681+17a9b157
Red Hat:advanced_virtualization:8.5::el8	libguestfs-java-devel	before 1:1.44.0-3.module+el8.5.0+10681+17a9b157	1:1.44.0-3.module+el8.5.0+10681+17a9b157
Red Hat:advanced_virtualization:8.5::el8	libguestfs-javadoc	before 1:1.44.0-3.module+el8.5.0+10681+17a9b157	1:1.44.0-3.module+el8.5.0+10681+17a9b157
Red Hat:advanced_virtualization:8.5::el8	libguestfs-man-pages-ja	before 1:1.44.0-3.module+el8.5.0+10681+17a9b157	1:1.44.0-3.module+el8.5.0+10681+17a9b157
Red Hat:advanced_virtualization:8.5::el8	libguestfs-man-pages-uk	before 1:1.44.0-3.module+el8.5.0+10681+17a9b157	1:1.44.0-3.module+el8.5.0+10681+17a9b157
Red Hat:advanced_virtualization:8.5::el8	libguestfs-rescue	before 1:1.44.0-3.module+el8.5.0+10681+17a9b157	1:1.44.0-3.module+el8.5.0+10681+17a9b157
Red Hat:advanced_virtualization:8.5::el8	libguestfs-rsync	before 1:1.44.0-3.module+el8.5.0+10681+17a9b157	1:1.44.0-3.module+el8.5.0+10681+17a9b157