[CVE-2026-64038][MODERATE REGULAR] hwmon: (lm90) Stop work before releasing hwmon device [ Upstream

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

CVE: CVE-2026-64038
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: hwmon: (lm90) Stop work before releasing hwmon device [ Upstream
Commit: c98107817b0f6cdf51adc5e84e75c39ee25d8b28
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=c98107817b0f6cdf51adc5e84e75c39ee25d8b28
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64038
Analysis date: Sun, 19 Jul 2026 22:22:32 -0400
ActionableScore: 3
ActionableScore lower bound: 2
Actionable bucket: Borderline manual review recommended
Manual review required: YES

Summary:
A cleanup ordering race in the lm90 hwmon driver can allow pending alert or report work to dereference a freed hwmon device during unbind or probe failure, causing a local kernel crash and requiring manual review as a UAF lifetime bug.

======================================================================
ABOUT THIS REPORT
======================================================================

The original Linux kernel CVE announcement for CVE-2026-64038 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64038

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 REGULAR
Manual review required: YES

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

======================================================================
AL-KERNEL CLASSIFICATION RESULT
======================================================================

CVE-2026-64038	MODERATE	CHECK WITH IMPACT FROM ORIG NN MODERATE	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:H/PR:H/UI:N/S:U/C:H/I:H/A:H';*CWE-416;CWE-362;*CWE-664;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '6.4';DESCR 'A race in the lm90 hwmon cleanup path can allow alert_work or report_work to run after the hwmon device has already been unregistered and freed. The worker path can then dereference the freed data hwmon_dev pointer in lm90_update_alarms(), making this a use after free candidate rather than a simple logic bug. For the CVSS the PR:H is used for the paranoid score because reliable triggering normally requires local administrative control over driver unbind, module removal, probe failure handling, or the underlying I2C device state. The issue is not network reachable and is tied to local device lifecycle operations. Impact is at least a local denial of service via kernel crash and in worst case may allow confidentiality or integrity impact due to kernel use after free, so it should be reviewed manually.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline manual review recommended (with actual score 3)	YES	INIT UAF HARDWARE  DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5	NO	NO	checked

======================================================================
ACTIONABLESCORE ANALYSIS
======================================================================

ActionableScore=3
ActionableScoreLower=2

## 1. ActionableScore

* Conservative score: 2
* Paranoid score: 3
* Final recommended bucket: **Borderline manual review recommended**::

## 2. Signal breakdown

Conservative signals:

* Race-UAF weak primitive: +1
  The patch describes a real use-after-free candidate where workqueue handlers may dereference `data->hwmon_dev` after the hwmon device has been unregistered and freed.
* Real lifetime corruption: +1
  This is a devm cleanup ordering and asynchronous work lifetime bug.
* Reliable kernel crash / strong DoS: +1
  A stale dereference of a freed hwmon device can plausibly cause an Oops or kernel crash.
* Requires admin/root/CAP_* in typical deployments: -2
  Reliable triggering normally requires driver unbind, module removal, probe failure control, or device lifecycle manipulation.
* Hard or timing-dependent race: -1
  The failure window requires pending alert/report work to run between hwmon device release and work cancellation.
* Privileged device-management lifetime path: +1
  The corruption occurs in a trusted driver cleanup path involving device registration, interrupts, and workqueue teardown.

Paranoid adjustment:

* Do not apply an additional rare-hardware penalty in the paranoid score.
  Although lm90 is device-specific, the affected pattern is a real kernel workqueue lifetime bug once the driver and hardware path exist.
* Do not add LPE plausibility.
  The patch does not show attacker-controlled reclaim, type confusion, callback dispatch, write-after-free, refcount takeover, or arbitrary write.

Call-site confidence: high.
The commit message directly names `lm90_alert_work()`, `lm90_report_alarms()`, `lm90_update_alarms()`, and the freed `data->hwmon_dev` dereference path.

## 3. Reachability analysis

The bug is local and device-lifecycle dependent. A typical attacker would need administrative control over driver unbind, module removal, probe failure conditions, or the I2C/hwmon device state. It is not network reachable.

Namespaces and containers generally do not make this reachable unless a container or service is delegated meaningful device-management privileges. Reduced-capability root or a management daemon with access to sysfs driver unbind paths could make the practical privilege model weaker than full host root, but that is deployment-specific.

The path is not broadly default-exposed to unprivileged users. It requires the lm90 driver and relevant hardware or emulated device path, plus a teardown or probe-failure sequence with pending work.

## 4. Severity interpretation

This behaves more like a low-to-borderline Moderate kernel lifetime bug than an Important-class vulnerability. The theoretical class is memory corruption because a freed kernel object can be dereferenced by asynchronous work. The realistic evidence points mainly to local DoS through crash during device teardown, not privilege escalation.

Manual review is still justified because it is a real UAF race in kernel driver lifecycle code. However, the lack of attacker-controlled reclaim, write-after-free, object replacement, or callback control keeps it below Actionable Moderate in the main scoring.

## 5. One-sentence report phrase

A cleanup ordering race in the lm90 hwmon driver can allow pending alert or report work to dereference a freed hwmon device during unbind or probe failure, causing a local kernel crash and requiring manual review as a UAF lifetime bug.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

Reason: this is a real race-dependent UAF candidate in kernel workqueue cleanup, even though practical triggering appears local, privileged, hardware-dependent, and primarily DoS-oriented.

======================================================================
UPSTREAM PATCH SUMMARY
======================================================================

Patch: hwmon: (lm90) Stop work before releasing hwmon device [ Upstream
Commit: c98107817b0f6cdf51adc5e84e75c39ee25d8b28
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=c98107817b0f6cdf51adc5e84e75c39ee25d8b28

Changed files:
  drivers/hwmon/lm90.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=c98107817b0f6cdf51adc5e84e75c39ee25d8b28

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

The original Linux kernel CVE announcement for CVE-2026-64038 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64038

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:L/AC:H/PR:H/UI:N/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS vector: AV:L/AC:H/PR:H/UI:N/S:U/C:H/I:H/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: 2
  Paranoid ActionableScore: 3

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: NO
Published priority for this report (same as in Subject): MODERATE REGULAR

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).