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CVE Record

CVE-2021-3735: A deadlock issue was found in the AHCI controller device of QEMU.

A deadlock issue was found in the AHCI controller device of QEMU. It occurs on a software reset (ahci_reset_port) while handling a host-to-device Register FIS (Frame Information Structure) packet from the guest. A privileged user inside the guest could use this flaw to hang the QEMU process on the host, resulting in a denial of service condition. The highest threat from this vulnerability is to system availability.

UnknownCVSS not scoredNot KEV-listedUpdated
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Glexia's TakeAutomated analysismoderate

Security readout for executives and security teams

Plain-English summary

CVE-2021-3735 is a QEMU availability issue. A privileged user inside a virtual machine can trigger a deadlock in the AHCI storage controller emulation, causing the QEMU process on the host to hang. Business impact is service interruption for affected virtual machines, not data theft or host code execution based on the provided sources.

Executive priority

Treat this as a moderate availability risk. It deserves patch tracking and prioritization on shared or externally managed virtualization platforms, but the provided evidence does not support emergency treatment for data breach or host takeover scenarios.

Technical view

The flaw is a deadlock in QEMU's AHCI controller device during ahci_reset_port while processing a guest-supplied host-to-device Register FIS packet. It is classified as CWE-667. The described security impact is denial of service against the host QEMU process, with availability as the primary concern.

Likely exposure

Exposure is most likely where QEMU is used with AHCI device emulation and guests have privileged users. The source bundle does not identify exact affected versions, configurations, or fixed releases, so asset validation must rely on vendor advisories and package metadata.

Exploitation context

The provided sources do not cite CISA KEV listing, active exploitation, or public weaponization. The described attacker position is already privileged inside a guest, limiting broad remote exposure but still relevant for shared virtualization, hosting, lab, and appliance environments.

Researcher notes

Version and fix details are incomplete in the supplied bundle. Analysis should stay scoped to QEMU AHCI emulation, privileged guest-triggered deadlock, and host-process denial of service. Do not infer code execution, data exposure, or active exploitation without additional vendor evidence.

Mitigation direction

  • Check QEMU, Red Hat, Debian, and product vendor advisories for fixed package guidance.
  • Prioritize updates on hosts running untrusted or multi-tenant guest workloads.
  • Restrict privileged access inside guests where operationally feasible.
  • Monitor affected virtualization hosts for hung QEMU processes and availability degradation.
  • Review NetApp guidance if using NetApp products that embed or depend on affected components.

Validation and detection

  • Inventory systems running QEMU and record package versions and vendor build channels.
  • Identify VMs configured with AHCI controller emulation.
  • Compare installed packages against Red Hat, Debian, NetApp, and QEMU advisory status.
  • Confirm whether affected hosts run untrusted, customer-managed, or shared guest workloads.
  • Verify monitoring detects stalled QEMU processes and guest availability loss.
Prepared
Confidence
medium
Sources
6

Public sources used

Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.

Potential ATT&CK relevance

Conservative CVE-to-ATT&CK context

These mappings and lookup hints may be relevant to the vulnerability behavior, CWE, affected product, or exposure path. Glexia-inferred context is not an official MITRE, ATT&CK, CWE, or CVE Program mapping.

ATT&CK lookup starting points

Use these exact CWE pages and searches to review the Glexia ATT&CK library from this CVE's weakness and description context.

cwe · low confidence lookup

CWE-667: Exact CWE lookup

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cve · low confidence lookup

CVE-2021-3735 mapping review

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Vulnerability profileCVE Program record
Severity
Unknown
CVSS
Not scored
Known Exploited
No
Published
Official CVE source material

CNA and ADP enrichment extracted from CVE v5

These fields come from the CVE record and ADP containers, not from Glexia's Take. They preserve time-varying source decisions such as CISA SSVC, KEV status, CVSS metrics, and provider references.

0CVSS vectors
0Timeline events
0ADP providers
5Source links

CVSS and timeline data

No CVSS vectors or timeline events were available in the normalized CVE source material.

Source materials

Affected products

Products and packages named in the record

VendorProductVersion / packageStatus
n/aQEMUNot KnownListed
Weakness

CWE details

CWE-667

CWE links open Glexia weakness intelligence pages with official CWE context, developer remediation guidance, and related CVE mappings.

CWE-667 · source CWE mapping

Improper Locking

Improper Locking represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.

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