[CVE-2026-64227][LOW] ACPI: driver: Check ACPI_COMPANION() against NULL during probe [ Upstream

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

CVE: CVE-2026-64227
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: ACPI: driver: Check ACPI_COMPANION() against NULL during probe [ Upstream
Commit: f1e12d81f9cd250e722da01c7670b518d4181406
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=f1e12d81f9cd250e722da01c7670b518d4181406
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64227
Analysis date: Fri, 24 Jul 2026 11:56:31 -0400
ActionableScore: 2
ActionableScore lower bound: 0
Actionable bucket: Ordinary Moderate / Low-like
Manual review required: NO

Summary:
Several ACPI platform drivers could dereference a NULL ACPI companion or handle when forced to probe a mismatched platform device via driver_override, causing a local kernel crash, with typical exploitation requiring administrative device binding privileges.

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

The original Linux kernel CVE announcement for CVE-2026-64227 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64227

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: LOW
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
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CVE-2026-64227	LOW	CHECK WITH IMPACT FROM ORIG NN MODERATE	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H';**CWE-476;*CWE-20;CWE-754;Other CVSS 'AV:L/AC:L/PR:H/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '5.5';DESCR 'Several ACPI platform drivers assumed that a probed platform_device always had an ACPI companion object or ACPI handle. Because device_match_driver_override can force a platform driver to bind to a device outside its normal ID match set, probe can run on a device with no ACPI companion and then dereference NULL. This can cause a kernel oops or panic and result in local denial of service. For the CVSS the PR:L is used for the paranoid score because some deployments may delegate driver binding or sysfs control to a reduced capability root, service account, or container admin rather than a fully trusted host administrator. The issue is not network reachable and is triggered through local driver binding control rather than packet traffic. Impact is denial of service only, with no evidence of UAF, OOB access, information disclosure, arbitrary write, or privilege escalation.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate / Low-like (with actual score 1)	YES	DANGER SIMPLEFIX HARDWARE  DECREASED_TO_MODERATE_REGULAR_FROM_MODERATE7_BASED_ON_GUESSCVSS_AND_CIANNH DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_ACTIONABLESCORELESSTHAN3	NO	NO	checked

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

ActionableScore=2
ActionableScoreLower=0

## 1. ActionableScore

* Conservative score: 0
* Paranoid score: 2
* Final recommended bucket: **Ordinary Moderate / Low-like**

## 2. Signal breakdown

Conservative signals:

* Reliable kernel crash / strong DoS: +1. Forced driver binding can make probe dereference a missing ACPI companion or ACPI handle, causing a NULL pointer dereference.
* Broad/default/common subsystem exposure: +1. ACPI platform drivers are common on affected systems.
* Requires admin/root/CAP_* in typical deployments: -2. Triggering requires local control over driver binding or driver_override style sysfs mechanisms, normally restricted to root or administrative users.

Conservative total: 0

Paranoid signals:

* Reliable kernel crash / strong DoS: +1. The failure mode is a kernel NULL pointer dereference during probe.
* Broad/default/common subsystem exposure: +1. The affected drivers include core ACPI device drivers.
* Privilege penalty reduced to 0 in paranoid interpretation. Some environments may delegate sysfs driver binding or device management to reduced-capability root, service accounts, or containerized admin roles, so this is not always equivalent to fully trusted host root.

Paranoid total: 2

Not awarded:

* No remote/network trigger.
* No generic memory corruption beyond NULL dereference.
* No UAF, OOB write, double free, type confusion, refcount abuse, arbitrary write, or callback control.
* No confidentiality or integrity impact supported.
* No practical privilege escalation path shown.

## 3. Reachability analysis

The bug is locally triggered through platform driver binding behavior, specifically because device_match_driver_override() can force a platform driver to probe a device outside its normal ID match set. In normal deployments, changing driver_override or binding devices through sysfs requires administrative privileges, so the conservative interpretation treats this as root/admin-only. Namespaces or containers may matter only if device-management sysfs access is delegated, which is uncommon but possible in specialized environments. The affected ACPI drivers are common, but the vulnerable path is not reached by normal network traffic or ordinary unprivileged user activity.

## 4. Severity interpretation

This behaves like an ordinary Moderate or Low-like local DoS issue rather than an Important-class vulnerability. The theoretical impact is a kernel crash from NULL pointer dereference during probe. Realistic exploitation evidence supports denial of service only. There is no demonstrated memory corruption primitive suitable for privilege escalation, no sensitive data exposure, and no cross-boundary security bypass beyond possible misuse of delegated device-management access.

## 5. One-sentence report phrase

Several ACPI platform drivers could dereference a NULL ACPI companion or handle when forced to probe a mismatched platform device via driver_override, causing a local kernel crash, with typical exploitation requiring administrative device binding privileges.

## 6. Manual review recommendation

NO MANUAL CHECK NEEDED

This is a validation hardening fix for NULL checks in privileged local probe paths, with no evidence of UAF, OOB write, information disclosure, privilege escalation, or remote reachability.

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

Patch: ACPI: driver: Check ACPI_COMPANION() against NULL during probe [ Upstream
Commit: f1e12d81f9cd250e722da01c7670b518d4181406
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=f1e12d81f9cd250e722da01c7670b518d4181406

Changed files:
  drivers/acpi/acpi_tad.c
  drivers/acpi/pfr_telemetry.c
  drivers/acpi/pfr_update.c
  drivers/acpi/thermal.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=f1e12d81f9cd250e722da01c7670b518d4181406

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

The original Linux kernel CVE announcement for CVE-2026-64227 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64227

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:L/PR:H/UI:N/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS vector: AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS score: 5.5

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: 0
  Paranoid ActionableScore: 2

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: LOW
KPANIC detected for this report: NO
Published priority for this report (same as in Subject): LOW

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).