CVE-2021-3735

Host process hang via AHCI software reset

Published Aug 26, 2022 · Updated Feb 28, 2025

Deadlock in QEMU's ich9-ahci controller allows guest OS users to hang the host QEMU process through an AHCI software reset. The handle_reg_h2d_fis function invokes ahci_reset_port while processing a host-to-device Register FIS, causing the controller path to deadlock. Exploitation requires privileged access inside a guest configured with ich9-ahci; the consequence is a hang of that virtual machine's QEMU process.

CVSS severity4.4
Medium
EPSS probability0.20%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Deadlock in QEMU's ich9-ahci controller allows guest OS users to hang the host QEMU process through an AHCI software reset. The handle_reg_h2d_fis function invokes ahci_reset_port while processing a host-to-device Register FIS, causing the controller path to deadlock. Exploitation requires privileged access inside a guest configured with ich9-ahci; the consequence is a hang of that virtual machine's QEMU process.

The record

CVE
CVE-2021-3735
Published
Aug 26, 2022
Updated
Feb 28, 2025
Vendor
QEMU Project
Product
QEMU
Classifications
CWE-400, CWE-667, T1499.004
Attack vector
local
Privileges
admin

Timeline

How it unfolded

  1. Aug 26, 2022CVE publishedPublication date reported by the CVE source.
  2. Feb 28, 2025Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

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  1. Affected versionversion=Not Known

What conditions does exploitation require?

Attack vectorlocal
Required privilegesadmin

What is affected?

QEMU Project · QEMUversion=Not Known

Published CVSS scores

4.4NIST NVDCVSS:3.1/AV:L/AC:L/PR:H/UI:N/S:U/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

CWE-400Uncontrolled Resource Consumption
CWE-667Improper Locking
T1499.004Application or System Exploitation

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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