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CVE Record

CVE-2021-3929: A DMA reentrancy issue was found in the NVM Express Controller (NVME) emulation in QEMU.

A DMA reentrancy issue was found in the NVM Express Controller (NVME) emulation in QEMU. This CVE is similar to CVE-2021-3750 and, just like it, when the reentrancy write triggers the reset function nvme_ctrl_reset(), data structs will be freed leading to a use-after-free issue. A malicious guest could use this flaw to crash the QEMU process on the host, resulting in a denial of service condition or, potentially, executing arbitrary code within the context of the QEMU process on the host.

UnknownCVSS not scoredNot KEV-listedUpdated
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Glexia's TakeAutomated analysishigh

Security readout for executives and security teams

Plain-English summary

CVE-2021-3929 affects QEMU’s emulated NVMe storage controller. A malicious virtual machine guest could trigger a memory safety bug in the QEMU process running on the host. The documented impact is host-side QEMU crash, with possible code execution in the QEMU process context.

Executive priority

Treat as high priority for virtualization platforms hosting untrusted workloads. The main confirmed risk is denial of service to host-side VM processes, with possible host-process code execution. Patch through vendor channels and validate guest NVMe exposure.

Technical view

The issue is a DMA reentrancy use-after-free in QEMU NVMe emulation. A reentrant write can trigger nvme_ctrl_reset(), freeing data structures that are still in use. Sources identify CWE-416, similarity to CVE-2021-3750, and a fix associated with qemu-kvm 7.0.0-rc0 and QEMU commit 736b01642d85be832385.

Likely exposure

Exposure is most likely where QEMU or qemu-kvm runs guests with the emulated NVMe controller enabled, especially when guests are untrusted or tenant-controlled. Standard hosts not using QEMU NVMe emulation are less likely exposed based on the supplied evidence.

Exploitation context

The supplied bundle does not show CISA KEV listing or active exploitation. Exploitation requires a malicious or compromised guest with access to the affected emulated NVMe device. Public issue and commit references exist, but no reliable exploit status is provided.

Researcher notes

Evidence supports a QEMU NVMe DMA reentrancy flaw leading to use-after-free during controller reset. The bundle names a fix point but lacks CVSS, affected version ranges, exploit maturity, and product-specific NetApp impact details. Avoid assuming broader product exposure without vendor confirmation.

Mitigation direction

  • Upgrade QEMU or qemu-kvm to a vendor-fixed build.
  • Confirm whether fixes include qemu-kvm 7.0.0-rc0 or vendor backports.
  • Apply relevant Red Hat, Fedora, NetApp, or platform vendor guidance.
  • Reduce use of emulated NVMe for untrusted guests where feasible.
  • Prioritize isolation controls for hosts running tenant-controlled guests.

Validation and detection

  • Inventory QEMU and qemu-kvm versions across virtualization hosts.
  • Identify VMs configured with QEMU emulated NVMe controllers.
  • Compare installed packages against vendor advisories and fixed builds.
  • Check vendor changelogs for CVE-2021-3929 or commit 736b01642d85be832385.
  • Review host QEMU crash logs for unexplained NVMe-related failures.
Prepared
Confidence
medium
Sources
8

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

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cwe · low confidence lookup

CWE-416: Exact CWE lookup

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description · low confidence lookup

Execution behavior lookup

The CVE wording references code or command execution, so execution technique review may help defensive triage. This is a Glexia inferred lookup path, not an official MITRE, ATT&CK, or CVE Program mapping.

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cve · low confidence lookup

CVE-2021-3929 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
8Source 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/aQEMUFixed in qemu-kvm 7.0.0-rc0Listed
Weakness

CWE details

CWE-416

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

CWE-416 · source CWE mapping

Use After Free

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

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