What is CVE-2021-3748?

CVE-2021-3748 is a high-severity vulnerability in Qemu, classified under Use After Free. CVSS score: 7.5/10. Published 2022-03-23.

How severe is CVE-2021-3748?

High severity. CVSS v3 base score is 7.5 out of 10.

Use After Free in Qemu

CVE-2021-3748

A use-after-free vulnerability was found in the virtio-net device of QEMU. It could occur when the descriptor's address belongs to the non direct access region, due to num_buffers being set after the virtqueue elem has been unmapped. A malicious guest could use this flaw to crash QEMU, resulting in a denial of service condition, or potentially execute code on the host with the privileges of the QEMU process.

Vulnerability class: Use-After-Free

Published 2022-03-23 · last modified 2026-06-17.

CVSS v3 metric

CVSS v3 base score 7.5 (High). Vector: CVSS:3.1/AV:L/AC:H/PR:H/UI:N/S:C/C:H/I:H/A:H.

EPSS exploit prediction

EPSS: 0.005 (44.3th percentile), scored 2026-11-01.

Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 44th percentile — 44.3% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS over last 30 days · oldest: 0.005 · newest: 0.005 · change: 0.000

Affected products

Qemu
Canonical Ubuntu Linux — versions 18.04, 20.04, 21.10
Debian Linux — versions 9.0, 10.0
Fedoraproject Fedora — versions 34
Red Hat Enterprise Linux — versions 8.0
Red Hat Enterprise Linux Advanced Virtualization Eus — versions 8.4
Qemu (Virtio-Net) — versions Affects qemu v0.10.0 and above, Fixed In – v6.2.0-rc0 and above.

Weakness classification (CWE)

CWE-416 — Use After Free

References

bugzilla.redhat.com/show_bug.cgi (Patch, Third Party Advisory, Issue Tracking)
ubuntu.com/security/CVE-2021-3748 (Patch, Third Party Advisory)
github.com/qemu/qemu/commit/bedd7e93d01961fcb16a97ae45d93acf357e11f6 (Patch, Third Party Advisory)
lists.nongnu.org/archive/html/qemu-devel/2021-09/msg00388.html (Patch, Mailing List, Third Party Advisory)
lists.debian.org/debian-lts-announce/2022/04/msg00002.html (mailing-list, Mailing List, Third Party Advisory)
security.netapp.com/advisory/ntap-20220425-0004/ (Third Party Advisory)
security.gentoo.org/glsa/202208-27 (vendor-advisory, Third Party Advisory)
lists.debian.org/debian-lts-announce/2022/09/msg00008.html (mailing-list, Mailing List, Third Party Advisory)

Frequently asked questions

What is CVE-2021-3748?: CVE-2021-3748 is a high-severity vulnerability in Qemu, classified under Use After Free. CVSS score: 7.5/10. Published 2022-03-23.
How severe is CVE-2021-3748?: High severity. CVSS v3 base score is 7.5 out of 10.