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.

Published: 2022-03-23 Last update: 2026-06-17 Assigner: [email protected] Source: [email protected]
NVD Status：Modified，CVE State: published
View at NVD, CVE.org, EUVD

CVE-2021-3748 is rated Moderate Risk (44.6/100): CVSS High severity, with low exploitation likelihood (EPSS 0.53%). 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-2021-3748

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 0.03% 0.53% +0.50%
2 2025-11-21 0.10% 0.03% -0.07%
3 2025-11-18 — 0.10% —

Full EPSS history (8 records total)

Common vulnerability scoring system (CVSS) metrics for CVE-2021-3748

CVSS metrics for this CVE.

Base score Version Severity Vector Exploitability Impact Score source
7.5 3.1 HIGH
CVSS:3.1/AV:L/AC:H/PR:H/UI:N/S:C/C:H/I:H/A:H Click to expand
Attack vector (AV:L)
They already need access on the box, or another person has to do something wrong; it’s not a remote drive-by.
Attack complexity (AC:H)
Even with access, the exploit needs extra luck, timing, or a fussy environment to actually work.
Privileges required (PR:H)
They need powerful rights—admin, root, or similar—before this pays off.
User interaction (UI:N)
Nobody has to click “OK” or open a trap file; it can work without a victim helping.
Scope (S:C)
Breaking this can reach past the original component and bite other resources—bigger blast radius.
Confidentiality (C:H)
Serious risk that confidential data gets exposed in a big way.
Integrity (I:H)
They could widely tamper with or forge data—trust in the data is badly hurt.
Availability (A:H)
Could take the service down hard or make it unusable for people who depend on it.
 0.8 6.0 [email protected]
6.9 2.0 MEDIUM
AV:L/AC:M/Au:N/C:C/I:C/A:C Click to expand
Access vector (AV:L)
Requires local access to the target system.
Access complexity (AC:M)
Exploitation needs some favorable conditions, but not exceptional ones.
Authentication (AU:N)
No authentication is required.
Confidentiality impact (C:C)
Complete confidentiality impact.
Integrity impact (I:C)
Complete integrity impact.
Availability impact (A:C)
Complete availability impact.
 3.4 10.0 [email protected]

Weakness enumeration for CVE-2021-3748

OS Trackers for CVE-2021-3748

vendor priority summary link
alpine high CVE-2021-3748: 1 source package rows (qemu); 23 state rows across 2 repos (3.22-community, edge-community); fixed 0, open 23. https://security.alpinelinux.org/vuln/CVE-2021-3748
debian not yet assigned CVE-2021-3748 not yet assigned priority: Debian including 1 source packages (qemu), 5 status rows across 5 suites (bookworm, bullseye, forky, sid, trixie): resolved 5. https://security-tracker.debian.org/tracker/CVE-2021-3748
gentoo high CVE-2021-3748: 1 GLSA(s) (202208-27), 1 atom(s) (app-emulation/qemu); latest impact high. https://bugs.gentoo.org/buglist.cgi?quicksearch=CVE-2021-3748
redhat medium — https://access.redhat.com/security/cve/CVE-2021-3748
suse medium CVE-2021-3748 severity moderate: SUSE including 781 source package names (0.45.0.7.7.56:qemu-5.2.0-106.4, 0.45.0.7.7.56:qemu-ipxe-1.0.0+-106.4, …), 1272 product×package rows across 65 product lines (Container suse/sle-micro-rancher/5.2, Container suse/sles/15.3/libguestfs-tools, … (65 product lines)): Fixed 1046, Known Affected 225, Known Not Affected 1. https://www.suse.com/security/cve/CVE-2021-3748/
ubuntu medium CVE-2021-3748 medium priority: Ubuntu including 1 source packages (qemu), 9 status rows across 9 suites (bionic, focal, hirsute, impish, jammy, kinetic, trusty, upstream, xenial): released 5, not-affected 2, ignored 1, needs-triage 1. https://ubuntu.com/security/CVE-2021-3748

Affected software / configurations for CVE-2021-3748

Vendor Product Version Raw CPE
qemu qemu >= 0.10.0, < 6.2.0 cpe:2.3:a:qemu:qemu:*:*:*:*:*:*:*:*
debian debian_linux 9.0 cpe:2.3:o:debian:debian_linux:9.0:*:*:*:*:*:*:*
debian debian_linux 10.0 cpe:2.3:o:debian:debian_linux:10.0:*:*:*:*:*:*:*
canonical ubuntu_linux 18.04 cpe:2.3:o:canonical:ubuntu_linux:18.04:*:*:*:lts:*:*:*
canonical ubuntu_linux 20.04 cpe:2.3:o:canonical:ubuntu_linux:20.04:*:*:*:lts:*:*:*
canonical ubuntu_linux 21.10 cpe:2.3:o:canonical:ubuntu_linux:21.10:*:*:*:*:*:*:*
fedoraproject fedora 34 cpe:2.3:o:fedoraproject:fedora:34:*:*:*:*:*:*:*
redhat enterprise_linux 8.0 cpe:2.3:o:redhat:enterprise_linux:8.0:*:*:*:advanced_virtualization:*:*:*
redhat enterprise_linux_advanced_virtualization_eus 8.4 cpe:2.3:o:redhat:enterprise_linux_advanced_virtualization_eus:8.4:*:*:*:*:*:*:*

References for CVE-2021-3748

cvelogic Threat Intelligence