CVE-2021-4207

Guest-to-host code execution via cursor dimension race

Published Apr 29, 2022 · Updated Mar 21, 2025

Heap-based buffer overflow in QEMU qemu-kvm 7.0.0 allows privileged guest OS users to crash the host process or execute code. The qxl_cursor function sizes the alpha-cursor object from cached dimensions but previously re-read guest-writable width and height for the copy length, allowing the guest to enlarge the transfer after allocation. Exploitation requires privileged guest control and an emulated QXL display; success crashes the QEMU process or runs code in that host process.

CVSS severity8.2
High
EPSS probability0.40%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
Coverage for this vulnerability

See if you're affected

Explore vulnerability checks for your environment with Hinoki.

Book a demo

Summary

What happened

Heap-based buffer overflow in QEMU qemu-kvm 7.0.0 allows privileged guest OS users to crash the host process or execute code. The qxl_cursor function sizes the alpha-cursor object from cached dimensions but previously re-read guest-writable width and height for the copy length, allowing the guest to enlarge the transfer after allocation. Exploitation requires privileged guest control and an emulated QXL display; success crashes the QEMU process or runs code in that host process.

The record

CVE
CVE-2021-4207
Published
Apr 29, 2022
Updated
Mar 21, 2025
Vendor
QEMU Project
Product
QEMU
Classifications
CWE-362, CWE-120, T1068, T1499
Attack vector
local
Privileges
admin

Timeline

How it unfolded

  1. Apr 29, 2022CVE publishedPublication date reported by the CVE source.
  2. Mar 21, 2025Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

Compare your product and version with the public record. A matching version still requires validation against your environment.

Is a vulnerable build present?

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

  1. Affected versionversion=qemu-kvm 7.0.0

What conditions does exploitation require?

Attack vectorlocal
Required privilegesadmin

What is affected?

QEMU Project · QEMUversion=qemu-kvm 7.0.0

Published CVSS scores

8.2NIST NVDCVSS:3.1/AV:L/AC:L/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.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

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-362Concurrent Execution using Shared Resource with Improper Synchronization ('Race Condition')
CWE-120Buffer Copy without Checking Size of Input ('Classic Buffer Overflow')
T1068Exploitation for Privilege Escalation
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

See the directory against your own environment.

Your stack

Check the software in your environment

Book a demo to see how Hinoki identifies affected software and validates exploitability in your environment.

Book a demo