[CVE-2026-64071][MODERATE 7.0] nvme-pci: fix use-after-free in nvme_free_host_mem() [ Upstream

[AL-KERNEL <alkernel@kernelcve.org>]

CVE: CVE-2026-64071
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: nvme-pci: fix use-after-free in nvme_free_host_mem() [ Upstream
Commit: 9525e3a6fbb1d126a22ab2ee86ddea25af581a7c
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=9525e3a6fbb1d126a22ab2ee86ddea25af581a7c
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64071
Analysis date: Sun, 19 Jul 2026 21:13:12 -0400
ActionableScore: 5
ActionableScore lower bound: 4
Actionable bucket: Actionable Moderate at minimum
Manual review required: YES

Summary:
A stale `dev->hmb_sgt` pointer in the NVMe PCI HMB cleanup path can cause a second `nvme_free_host_mem()` call to reuse freed DMA scatter-gather metadata, leading to a kernel crash during device probe error handling.

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ABOUT THIS REPORT
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The original Linux kernel CVE announcement for CVE-2026-64071 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64071

The original announcement does not normally provide a security severity
estimate, CVSS assessment, or enough information to determine whether the
reported kernel bug represents a practically relevant security issue.

This report was generated by AL-KERNEL, an AI-assisted Linux kernel
vulnerability analysis system developed by Alexander Larkin. It combines
an autonomous classifier with LLM-assisted technical analysis and a
separate ActionableScore mechanism.

The purpose of this report is to prioritize Linux kernel CVEs before
manual review, identify cases that require prompt investigation, and
support automatic closure of issues that are unlikely to have meaningful
security impact.

Published priority for this report: MODERATE 7.0
Manual review required: YES

A detailed explanation of the methodology and priority rules is included
at the end of this message.

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AL-KERNEL CLASSIFICATION RESULT
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CVE-2026-64071	MODERATE	CHECK WITH IMPACT FROM ORIG NN MODERATE	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:A/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:H';*CWE-416;CWE-415;**CWE-476;Other CVSS 'AV:A/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '6.4';DESCR 'A use-after-free condition in the NVMe/PCI host memory buffer cleanup path can occur because nvme_free_host_mem frees dev hmb_sgt but leaves the pointer stale. If HMB allocation succeeds and nvme_set_host_mem later fails during probe, the error path can call nvme_free_host_mem twice and the second call may pass a freed sg table to dma_free_noncontiguous, causing a kernel crash. For the CVSS the PR:N is used because a malicious or failing attached NVMe device can trigger the probe error path without a user account on the host. In local reprobe scenarios administrative privileges may be required. The issue is not reachable from an IP network and is tied to an attached PCIe or Thunderbolt storage path. Impact is at least denial of service via kernel crash. In the paranoid interpretation, limited confidentiality or integrity impact is kept for manual review because the primitive is a kernel use-after-free candidate, but the provided context mainly supports crash behavior.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate at minimum (with actual score 5)	YES	DANGER NULLPTR NVME ERRORPATH UAF HARDWARE LINUS KPANIC MEMORY 	YES	NO	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=5
ActionableScoreLower=4

## 1. ActionableScore

* Conservative score: 4
* Paranoid score: 5
* Final recommended bucket: **Actionable Moderate at minimum**::

## 2. Signal breakdown

* Firmware-mediated external influence: +1. A failing or malicious attached NVMe device can influence the probe and HMB setup error path.
* Generic memory corruption, weak to medium UAF candidate: +1 conservative, +2 paranoid. The bug is a stale pointer after free and second cleanup call, but the demonstrated result is a NULL dereference rather than controlled reclaim or overwrite.
* Real lifetime corruption: +1. `dev->hmb_sgt` remains stale after `dma_free_noncontiguous()`.
* Reliable kernel crash / strong DoS: +1. The commit provides a concrete NULL pointer dereference trace in `iommu_dma_free_noncontiguous()`.
* Important filesystem/storage path: +1. NVMe PCI is a core storage driver path.
* Privileged kernel/device-management memory corruption path: +1. The issue occurs in driver probe and DMA-adjacent cleanup.
* Hard or special triggering conditions: -1. Triggering needs HMB setup success followed by `nvme_set_host_mem()` failure in the same probe path.
* Constrained primitive / no attacker-controlled payload shown: -1. The patch supports stale pointer reuse and crash, but not controlled object replacement, arbitrary write, or callback control.

## 3. Reachability analysis

The most realistic trigger is a failing, unstable, or malicious attached NVMe device, especially via PCIe or Thunderbolt where HMB setup can fail during probe. A local user generally cannot trigger this reliably without administrative control over device reprobe, hotplug, or hardware attachment. Namespaces and containers do not materially lower the privilege requirement because this is a host PCI/NVMe probe path, not a namespaced local API. The path is relevant on systems using NVMe PCI devices with Host Memory Buffer support, but it is not IP-network reachable.

## 4. Severity interpretation

This behaves above an ordinary Moderate because it is a real kernel lifetime bug in a storage driver cleanup path and has a demonstrated crash. It does not reach a strong Important classification conservatively because the observed primitive is a stale freed `sg_table` dereference leading to NULL pointer dereference, with no shown attacker-controlled reclaim, overwrite target, type confusion, or privilege escalation chain. The paranoid score is kept at Actionable Moderate because UAF and double-cleanup bugs in DMA-adjacent storage paths deserve manual review even when the current evidence mainly supports DoS.

## 5. One-sentence report phrase

A stale `dev->hmb_sgt` pointer in the NVMe PCI HMB cleanup path can cause a second `nvme_free_host_mem()` call to reuse freed DMA scatter-gather metadata, leading to a kernel crash during device probe error handling.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED. YES REQUIRES MANUAL CHECK.

Reason: this is a real UAF / double-cleanup candidate in a DMA-adjacent NVMe PCI storage path, with demonstrated kernel crash and enough lifetime complexity to justify manual triage, although practical privilege escalation is not demonstrated.

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UPSTREAM PATCH SUMMARY
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Patch: nvme-pci: fix use-after-free in nvme_free_host_mem() [ Upstream
Commit: 9525e3a6fbb1d126a22ab2ee86ddea25af581a7c
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=9525e3a6fbb1d126a22ab2ee86ddea25af581a7c

Changed files:
  drivers/nvme/host/pci.c

Diff excerpt:

Not included in this email. See the upstream URL for the full patch.

Full patch:
https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=9525e3a6fbb1d126a22ab2ee86ddea25af581a7c

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DETAILED REPORT METHODOLOGY
======================================================================

The original Linux kernel CVE announcement for CVE-2026-64071 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64071

The original CVE announcement normally does not include a security-level
estimate. In particular, it may not contain a CVSS assessment, an impact
level, or enough information to determine whether the reported bug is a
practically relevant security issue. One purpose of this parallel CVE list
is to provide that missing technical and prioritization information.

The original goal of the AL-KERNEL project was to prioritize Linux kernel
CVE analysis automatically before manual review. The system can also help
identify non-security issues that may be suitable for automatic closure.

This report was generated by AL-KERNEL, an AI-assisted Linux kernel
vulnerability analysis system developed by Alexander Larkin.

The first analysis stage combines an autonomous classifier with additional
LLM-based analysis. The autonomous classifier runs locally on a CPU and is
based on a backpropagation neural network. Together, these mechanisms
produce a technical vulnerability description, identify likely weakness
types, estimate CVSS severity, and provide input for ActionableScore.

Two CVSS estimates are retained because incomplete kernel vulnerability
information often permits more than one defensible interpretation:

  Conservative CVSS vector: AV:A/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS vector: AV:A/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:H
  The Best / paranoid CVSS score: 6.4

The conservative vector represents a lower-impact interpretation.
The Best/paranoid vector intentionally represents a plausible upper-bound
interpretation and should not automatically be treated as demonstrated
real-world impact.

CVSS may also need to be adjusted for a particular Linux deployment,
because actual reachability, privileges, enabled kernel configuration,
hardware, namespaces, exposed device nodes, and other environmental
conditions can differ significantly between systems.

A separate ActionableScore mechanism evaluates practical remediation
urgency. Its analysis may include reachability, attack prerequisites,
subsystem exposure, memory-corruption characteristics, denial-of-service
reliability, and possible confidentiality, integrity, or
privilege-escalation impact.

  Conservative ActionableScore: 4
  Paranoid ActionableScore: 5

The final base severity is taken directly from the second tab-separated
field of the AL-KERNEL classification result. ActionableScore does not
replace or independently override that final AL-KERNEL decision, and
if ActionableScore adjusted impact level of ALKERNEL, then you would see
self-readable flags above like INCREASED_TO_HIGH_BASED_ON_ACTIONABLESCOREHIGHEREQTHAN7.

For an AL-KERNEL result of MODERATE, this report uses the following
additional presentation split:

  ActionableScore below 5   -> MODERATE REGULAR
  ActionableScore 5 or more -> MODERATE 7.0

The distinction between MODERATE REGULAR and MODERATE 7.0 makes it
possible to identify Moderate issues that should receive manual analysis
and fixes before lower-priority MODERATE REGULAR issues. In many cases,
MODERATE REGULAR fixes may wait for a later rebase or routine update.

There is one override in which MODERATE REGULAR becomes MODERATE 7.0
even when the ActionableScore is below 5. When the AL-KERNEL result
contains the KPANIC flag, a MODERATE result is always presented as
MODERATE 7.0. The KPANIC flag selected with few regexps without
usage of AI at all, so it helps to detect cases when Kernel Crash happens
and similar (to filter False-Negative results from the LLM usage).

KPANIC indicates that a reliable kernel crash, kernel panic, or similarly
serious kernel availability impact was identified by the classification
workflow.

AL-KERNEL base severity for this report: MODERATE
KPANIC detected for this report: YES
Published priority for this report (same as in Subject): MODERATE 7.0

These results are intended to support engineering triage. They are
machine-generated estimates, and cases marked for manual review should
be validated by a human security engineer before final disposition.
For more info read docs linked from here: https://kernelcve.org/
(and you can submit you own patch there to generate such a report
for non-existant CVE-id yet).

Note that in many cases this AI tool selects higher severity, than
real is (means you can expect Importants instead of Moderate 7.0 or
Moderates 7.0 instead of regular Moderates). If you see such cases,
please use reply email interface to add additional manual analyses
info to this particular CVE.
And please, please, let me know when you see Lows instead of Importants
or Important instead of Low (because particular for such cases I
need to tune this AI tool to make it better for this one and next similar).
My contact email for such notifications is alexanjelausa@gmail.com (and both
send reply to CVE record itself too and see "reply" button below for howto reply).