[CVE-2026-74552][MODERATE REGULAR] hwmon: (lm90) Only report alarms if driver is ready [ Upstream

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

CVE: CVE-2026-74552
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: hwmon: (lm90) Only report alarms if driver is ready [ Upstream
Commit: 4eed33c7db5c0c573928d28d8a2c003642c679b8
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=4eed33c7db5c0c573928d28d8a2c003642c679b8
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74552
Analysis date: Sat, 15 Aug 2026 16:40:14 -0400
ActionableScore: 1
ActionableScore lower bound: unknown
Actionable bucket: Ordinary Moderate / Low-like
Manual review required: NO

Summary:
A local race in the lm90 hwmon driver can allow userspace sysfs reads during device registration to schedule alarm reporting before `data->hwmon_dev` is initialized, causing a NULL pointer dereference and kernel DoS.

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

The original Linux kernel CVE announcement for CVE-2026-74552 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74552

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: NO

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
======================================================================

CVE-2026-74552	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:L/UI:N/S:U/C:N/I:N/A:H';**CWE-476;CWE-362;CWE-665;BEST CVSS score: '4.7';DESCR 'A NULL pointer dereference in the lm90 hwmon driver can occur during driver registration because userspace may read sysfs attributes before data hwmon_dev is initialized. The read path can call lm90_update_device() and lm90_update_alarms_locked(), which may schedule report_work and later pass a NULL hwmon device pointer to hwmon_notify_event(). For the CVSS the PR:L is used because a local user process can trigger sysfs reads, although reliable triggering depends on racing the short device registration window. The issue is not network reachable and requires local execution on the affected host. Impact is denial of service via kernel crash or Oops, with no concrete evidence of confidentiality or integrity impact from the patch context.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate / Low-like (with actual score 1)	YES	NULLPTR SIMPLEFIX  DECREASED_TO_MODERATE_REGULAR_FROM_MODERATE7_BASED_ON_GUESSCVSS_AND_CIANNH	NO	NO	checked

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

ActionableScore=1

## 1. ActionableScore

* Conservative score: 1
* Paranoid score: 1
* Final recommended bucket: **Ordinary Moderate / Low-like**

## 2. Signal breakdown

Triggered signals:

* Local unprivileged trigger: +1
  Userspace can read hwmon sysfs attributes, and this may be possible for a local unprivileged process while the lm90 device is still completing registration.

* Reliable kernel crash / strong DoS: +1
  The described failure is a NULL pointer dereference through `hwmon_notify_event()` with `data->hwmon_dev == NULL`, which can crash or Oops the kernel depending on configuration.

Subtracted signals:

* Hard or unreliable race / special timing required: -1
  The trigger requires hitting a short registration window immediately after `devm_hwmon_device_register_with_info()` and before `data->hwmon_dev` is initialized.

No additional points:

* No remote or network reachability.
* No UAF, double free, OOB write, refcount corruption, type confusion, or attacker-controlled object reuse.
* No confidentiality or integrity impact supported by the patch.
* No practical privilege escalation path is shown.
* No broad default exposure beyond systems with an affected lm90-compatible hwmon device and readable sysfs attributes.

## 3. Reachability analysis

A local userspace process may trigger the issue by reading hwmon sysfs attributes during the lm90 driver registration window. This does not require network access and is not packet-triggerable. Namespaces do not substantially improve reachability unless the relevant sysfs hwmon attributes are exposed inside a container. The affected path depends on the lm90 driver being present and bound to compatible hardware or a corresponding emulated device, so exposure is configuration and hardware dependent.

Call-site confidence: high. The commit message describes the concrete path from sysfs read to `lm90_update_device()`, `lm90_update_alarms_locked()`, `schedule_work()`, `lm90_report_alarms()`, and finally `hwmon_notify_event()` with a NULL `hwmon_dev`.

## 4. Severity interpretation

This behaves like an ordinary Moderate or Low-like kernel DoS issue, not an Important-class vulnerability. The bug is a local initialization race leading to NULL pointer dereference. Theoretical memory corruption potential is weak because the patch only prevents scheduling workers before a pointer is initialized, and there is no evidence of stale object reuse, attacker-controlled reclaim, write-after-free, callback control, or object confusion. Realistic exploitation evidence supports local crash only.

## 5. One-sentence report phrase

A local race in the lm90 hwmon driver can allow userspace sysfs reads during device registration to schedule alarm reporting before `data->hwmon_dev` is initialized, causing a NULL pointer dereference and kernel DoS.

## 6. Manual review recommendation

MANUAL CHECK RECOMMENDED

Reason: the actionable score is low, but this is still a kernel race with crash impact. Manual review should mainly confirm whether affected systems actually load the lm90 driver, expose the relevant hwmon sysfs attributes, and allow unprivileged reads during device registration.

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

Patch: hwmon: (lm90) Only report alarms if driver is ready [ Upstream
Commit: 4eed33c7db5c0c573928d28d8a2c003642c679b8
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=4eed33c7db5c0c573928d28d8a2c003642c679b8

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=4eed33c7db5c0c573928d28d8a2c003642c679b8

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

The original Linux kernel CVE announcement for CVE-2026-74552 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74552

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: Not available
  The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS score: 4.7

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: unknown
  Paranoid ActionableScore: 1

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).