CVE-2021-3546

Guest-to-host code execution via zero-size capability buffer

Published Jun 2, 2021 · Updated Aug 3, 2024

Out-of-bounds write in QEMU 6.0 and earlier allows privileged guest OS users to crash the host QEMU process via a GET_CAPSET command. In virgl_cmd_get_capset(), a zero max_size produces a response allocation with no capability-data space before virgl_renderer_fill_caps writes after it. The vhost-user-gpu device must be configured and controlled from a guest; successful corruption causes a host process crash or code execution with that process's privileges.

CVSS severity8.2
High
EPSS probability0.46%
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

Out-of-bounds write in QEMU 6.0 and earlier allows privileged guest OS users to crash the host QEMU process via a GET_CAPSET command. In virgl_cmd_get_capset(), a zero max_size produces a response allocation with no capability-data space before virgl_renderer_fill_caps writes after it. The vhost-user-gpu device must be configured and controlled from a guest; successful corruption causes a host process crash or code execution with that process's privileges.

The record

CVE
CVE-2021-3546
Published
Jun 2, 2021
Updated
Aug 3, 2024
Vendor
QEMU Project
Product
QEMU
Classifications
CWE-787, T1499.004, T1068
Attack vector
local
Privileges
admin

Timeline

How it unfolded

  1. Jun 2, 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

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=All QEMU versions up to and including 6.0

What conditions does exploitation require?

Attack vectorlocal
Required privilegesadmin

What is affected?

QEMU Project · QEMUversion=All QEMU versions up to and including 6.0

Published CVSS scores

8.2NVDCVSS:3.1/AV:L/AC:L/PR:H/UI:N/S:C/C:H/I:H/A:H
6.5SUSECVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
4.6NVDAV:L/AC:L/Au:N/C:P/I:P/A:P

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 9, 2026Sep 15, 2026
Latest reporting daySep 15, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectorlocal
Privilegesadmin
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-787Out-of-bounds Write
T1499.004Application or System Exploitation
T1068Exploitation for Privilege Escalation

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