CVE-2021-3748

Guest-triggered host crash via virtio-net use-after-free

Published Mar 23, 2022 · Updated Aug 3, 2024

Use-after-free in QEMU virtio-net before 6.2.0 allows malicious guest drivers to crash QEMU or execute code on the host. The virtio_net_receive_rcu function writes num_buffers after unmapping descriptor scatter-gather elements, leaving freed bounce-buffer memory referenced. A guest must control virtio-net descriptors; exploitation can interrupt the emulator or run code with QEMU process privileges.

CVSS severity7.5
High
EPSS probability0.52%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Use-after-free in QEMU virtio-net before 6.2.0 allows malicious guest drivers to crash QEMU or execute code on the host. The virtio_net_receive_rcu function writes num_buffers after unmapping descriptor scatter-gather elements, leaving freed bounce-buffer memory referenced. A guest must control virtio-net descriptors; exploitation can interrupt the emulator or run code with QEMU process privileges.

The record

CVE
CVE-2021-3748
Published
Mar 23, 2022
Updated
Aug 3, 2024
Vendor
QEMU Project
Product
QEMU
Classifications
CWE-416, T1611
Attack vector
local
Privileges
authenticated

Timeline

How it unfolded

  1. Mar 23, 2022CVE publishedPublication date reported by the CVE source.
  2. Aug 3, 2024Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=Affects qemu v0.10.0 and above, Fixed In – v6.2.0-rc0 and above.

What conditions does exploitation require?

Attack vectorlocal
Required privilegesauthenticated

What is affected?

QEMU Project · QEMUversion=Affects qemu v0.10.0 and above, Fixed In – v6.2.0-rc0 and above.

Published CVSS scores

7.5UbuntuCVSS:3.1/AV:L/AC:H/PR:H/UI:N/S:C/C:H/I:H/A:H

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

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No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectorlocal
Privilegesauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-416Use After Free
T1611Escape to Host

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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