CVE-2021-20221

Host denial of service via unmasked interrupt ID

Published May 13, 2021 · Updated Aug 3, 2024

Out-of-bounds access in QEMU up to 4.2.0 allows guest OS users to crash the host emulator via a crafted interrupt ID. The ARM Generic Interrupt Controller emulator writes the software-generated interrupt ID without masking it to four bits, allowing an oversized index into controller state arrays. Exploitation requires a privileged guest, an aarch64 setup using kernel-irqchip=off, and can terminate the QEMU process; the default kernel-irqchip=on configuration is unaffected.

CVSS severity6.0
Medium
EPSS probability0.33%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Out-of-bounds access in QEMU up to 4.2.0 allows guest OS users to crash the host emulator via a crafted interrupt ID. The ARM Generic Interrupt Controller emulator writes the software-generated interrupt ID without masking it to four bits, allowing an oversized index into controller state arrays. Exploitation requires a privileged guest, an aarch64 setup using kernel-irqchip=off, and can terminate the QEMU process; the default kernel-irqchip=on configuration is unaffected.

The record

CVE
CVE-2021-20221
Published
May 13, 2021
Updated
Aug 3, 2024
Vendor
QEMU Project
Product
QEMU
Classifications
T1499.004
Attack vector
local
Privileges
admin

Timeline

How it unfolded

  1. May 13, 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=up to, including qemu 4.2.0

What conditions does exploitation require?

Attack vectorlocal
Required privilegesadmin

What is affected?

QEMU Project · QEMUversion=up to, including qemu 4.2.0

Published CVSS scores

6.0Oracle Linux CVE RepositoryCVSS:3.0/AV:L/AC:L/PR:H/UI:N/S:C/C:N/I:N/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
Privilegesadmin
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

T1499.004Endpoint Denial of Service: Application or System Exploitation

Public exploit references

No public exploit references are available in this record.

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Technologies

Your stack

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Your stack

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