[CVE-2026-46021][MODERATE 7.0] thermal: core: Fix thermal zone governor cleanup issues [ Upstream

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

CVE: CVE-2026-46021
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: thermal: core: Fix thermal zone governor cleanup issues [ Upstream
Commit: 37a430a2d4e66ec8238da6c7f7e48809bf265e13
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=37a430a2d4e66ec8238da6c7f7e48809bf265e13
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-46021
Analysis date: Wed, 27 May 2026 12:20:33 -0400
ActionableScore: 7
ActionableScore lower bound: 4
Actionable bucket: Strong Important candidate / Actionable Moderate at minimum
Manual review required: YES

Summary:
A thermal core race between governor cleanup and sysfs governor update can cause a local UAF in thermal zone teardown, likely leading to kernel crash and requiring review for broader lifetime-corruption impact.

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

The original Linux kernel CVE announcement for CVE-2026-46021 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-46021

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.

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

CVE-2026-46021	MODERATE	CHECK	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H';*CWE-416;CWE-362;CWE-667;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '7';DESCR 'A use after free can occur in thermal core cleanup because thermal_zone_device_unregister() called thermal_set_governor() without holding the thermal zone lock while sysfs governor updates could run concurrently. A racing unregister and policy update can leave governor private state or thermal zone state accessed after cleanup. For the CVSS the PR:L is used in the paranoid score only for environments where thermal policy or device management is delegated to a reduced privilege service or container. The typical case is closer to PR:H because unregister and sysfs governor control usually require administrative privileges. The issue is not network reachable and does not involve out of bounds access or arbitrary write. Impact is at least denial of service via kernel crash. Because this is a real local UAF race in thermal device cleanup, worst case confidentiality and integrity impact should be reviewed manually even though reliable exploitation is not demonstrated.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 6)	YES	OOB RACE LEAK ERRORPATH UAF HARDWARE  KPANIC INCREASED_TO_MODERATE_FROM_LOW_BASED_ON_GUESSCVSS	NO	NO	checked

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

ActionableScore=7
ActionableScoreLower=4

## 1. ActionableScore

* Conservative score: 4
* Paranoid score: 7
* Final recommended bucket: **Strong Important candidate / Actionable Moderate at minimum**::

## 2. Signal breakdown

Conservative signals:

* Generic memory corruption, strong corruption primitive: +2
  The commit explicitly identifies a UAF race in thermal governor cleanup.

* Real lifetime corruption: +1
  The bug involves cleanup of governor private state while sysfs governor update can access or modify related state concurrently.

* Reliable kernel crash / strong DoS: +1
  A UAF in thermal cleanup can crash the kernel.

* Privileged kernel/device-management path: +1
  The race involves thermal zone unregister and device management cleanup.

Subtracting signals:

* Requires admin/device-management in typical deployments: -2
  Thermal zone unregister and governor policy control are normally privileged.

* Hard race / special timing required: -1
  Requires concurrent unregister and sysfs governor update.

Paranoid additions:

* Reduced-privilege management concern: +1
  Some systems delegate thermal policy or device management to services, containers, or platform daemons with reduced privileges.

* Privilege escalation plausible: +2
  UAF in a kernel subsystem cleanup path may be exploitable beyond crash if object lifetime and reclaim can be influenced, though no exploit primitive is shown.

* Confidentiality/integrity impact plausible: +1
  UAF may theoretically expose or corrupt stale kernel state if the freed object is reused.

## 3. Reachability analysis

The realistic trigger is local and management-oriented: one path unregisters or removes a thermal zone while another updates the governor through sysfs. In common deployments, both operations are restricted to root or platform management daemons.

Namespaces and containers matter only if thermal sysfs or device management is delegated. The issue is not network reachable.

## 4. Severity interpretation

This is stronger than an ordinary Moderate cleanup bug because it is a real UAF race. Conservative impact is kernel crash during thermal cleanup or governor update.

The paranoid score treats it as a Strong Important candidate due to lifetime corruption. Practical exploitation is constrained by privilege requirements and timing, and there is no demonstrated LPE primitive.

## 5. One-sentence report phrase

A thermal core race between governor cleanup and sysfs governor update can cause a local UAF in thermal zone teardown, likely leading to kernel crash and requiring review for broader lifetime-corruption impact.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

Reason: this is a real UAF race in kernel thermal cleanup, even though normal triggering requires privileged or delegated device-management access.

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

Patch: thermal: core: Fix thermal zone governor cleanup issues [ Upstream
Commit: 37a430a2d4e66ec8238da6c7f7e48809bf265e13
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=37a430a2d4e66ec8238da6c7f7e48809bf265e13

Changed files:
  drivers/thermal/thermal_core.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=37a430a2d4e66ec8238da6c7f7e48809bf265e13

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

The original Linux kernel CVE announcement for CVE-2026-46021 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-46021

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:L/UI:N/S:U/C:H/I:H/A:H
  The Best / paranoid CVSS score: 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: 4
  Paranoid ActionableScore: 7

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).