CVE-2021-20203

Host process crash via unchecked vmxnet3 parameters

Published Feb 25, 2021 · Updated Aug 3, 2024

Integer overflow in QEMU 5.2.0 and earlier allows guest OS users to crash the host QEMU process through crafted vmxnet3 parameters. vmxnet3_activate_device() passes guest-controlled MTU and transmit, completion, and receive ring sizes into device setup without enforcing defined bounds. Exploitation requires high privileges in a guest configured with the vmxnet3 adapter, and the bounded consequence is interruption of that QEMU instance.

CVSS severity3.2
Low
EPSS probability0.59%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Integer overflow in QEMU 5.2.0 and earlier allows guest OS users to crash the host QEMU process through crafted vmxnet3 parameters. vmxnet3_activate_device() passes guest-controlled MTU and transmit, completion, and receive ring sizes into device setup without enforcing defined bounds. Exploitation requires high privileges in a guest configured with the vmxnet3 adapter, and the bounded consequence is interruption of that QEMU instance.

The record

CVE
CVE-2021-20203
Published
Feb 25, 2021
Updated
Aug 3, 2024
Vendor
QEMU Project
Product
QEMU
Classifications
CWE-190, T1499
Attack vector
local
Privileges
admin

Timeline

How it unfolded

  1. Feb 25, 2021CVE 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=versions up to v5.2.0

What conditions does exploitation require?

Attack vectorlocal
Required privilegesadmin

What is affected?

QEMU Project · QEMUversion=versions up to v5.2.0

Published CVSS scores

3.2UbuntuCVSS:3.1/AV:L/AC:L/PR:H/UI:N/S:C/C:N/I:N/A:L

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
Privilegesadmin
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-190Integer Overflow or Wraparound
T1499Endpoint Denial of Service

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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