[CVE-2026-64603][LOW] platform/x86: intel-hid: Protect ACPI notify handler against recursion

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

CVE: CVE-2026-64603
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: platform/x86: intel-hid: Protect ACPI notify handler against recursion
Commit: a6402808e552e44e9c26a9fe8395ac11703d5800
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=a6402808e552e44e9c26a9fe8395ac11703d5800
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64603
Analysis date: Thu, 06 Aug 2026 04:07:10 -0400
ActionableScore: 2
ActionableScore lower bound: 1
Actionable bucket: Ordinary Moderate / Low-like
Manual review required: NO

Summary:
A race in the intel-hid ACPI notify handler on affected convertible or detachable systems can double-register the lazy SW_TABLET_MODE input device and later trigger a NULL pointer dereference, causing a local or firmware-mediated denial of service.

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ABOUT THIS REPORT
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The original Linux kernel CVE announcement for CVE-2026-64603 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64603

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-2026-64603	LOW	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-362;**CWE-476;CWE-667;Other CVSS 'AV:P/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '4.7';DESCR 'A race in the intel-hid ACPI notify_handler can occur because the same handler may run concurrently on multiple CPUs. On affected convertible and detachable systems, SW_TABLET_MODE input support is initialized lazily on the first tablet mode event. Two racing events can both pass the missing switches check and register the same input device twice, leading to a duplicate sysfs entry and a later NULL pointer dereference. For the CVSS the PR:L is used in the paranoid vector only for environments where a local user or local process can repeatedly trigger the platform event path. The base scenario is closer to physical access because the event normally comes from tablet mode hardware or firmware. The issue is not network reachable. Impact is denial of service via kernel crash, with no supported confidentiality or integrity impact.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate / Low-like (with actual score 2)  SKIP CVE-2026-64603 UNKNOWN SKIP No affected files built, so skip this CVE NO  - - unknown 	MAYBE	OOB NULLPTR USB INIT SIMPLEFIX RACE HARDWARE  DECREASED_TO_MODERATE_REGULAR_FROM_MODERATE7_BASED_ON_GUESSCVSS_AND_CIANNH DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_ACTIONABLESCORELESSTHAN3	-	-	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=2
ActionableScoreLower=1

## 1. ActionableScore

* Conservative score: 1
* Paranoid score: 2
* Final recommended bucket: **Ordinary Moderate / Low-like**

## 2. Signal breakdown

Conservative signals:

* Firmware-mediated external influence: +1. The trigger is an ACPI notify event generated through platform firmware or convertible or detachable hardware state changes.
* Reliable kernel crash / strong DoS: +1. The commit explicitly says the race can cause duplicate sysfs registration followed by a NULL pointer dereference.
* Hard or unreliable race / special timing required: -1. Two ACPI notify handler executions must race on different CPUs and both pass the same lazy initialization check.

Paranoid additional signal:

* Local unprivileged trigger: +1. In the most conservative practical interpretation, a local user on affected hardware might repeatedly induce tablet-mode transitions or related platform events, though this is not a normal software-only unprivileged API.

Not applied:

* No generic memory corruption bonus. The described failure is duplicate registration followed by NULL pointer dereference, not UAF, OOB write, double free, type confusion, or controlled overwrite.
* No privilege escalation bonus. There is no reclaim, stale callback, write-after-free, object replacement, or attacker-controlled memory reuse shown.
* No confidentiality or integrity impact. The patch and commit support DoS only.

## 3. Reachability analysis

The bug is reachable only on affected Intel HID platforms, mainly convertibles and detachables where SW_TABLET_MODE support is registered lazily from the ACPI notify handler. The base trigger is closer to hardware or firmware event delivery than a normal local syscall or network API. Namespaces and containers do not materially reduce the privilege requirement because the affected path is platform ACPI notification handling, not a namespaced kernel interface. The path is not network reachable and is not a broad default server exposure. Realistic exploitation requires affected hardware plus a race between concurrent notify handler invocations.

Call-site confidence: high, because the patch shows the raced handler, the lazily initialized field, and the mutex added directly around notify_handler.

## 4. Severity interpretation

This behaves like an ordinary Moderate or Low-like kernel DoS issue, not an Important-class vulnerability. The theoretical issue is a race in kernel object registration state, but the demonstrated consequence is a duplicate sysfs entry and NULL pointer dereference. There is no evidence of a practical memory corruption primitive, privilege escalation path, data leak, or cross-boundary policy bypass. The main risk is local or firmware-mediated crash on a narrow class of laptops or tablets.

## 5. One-sentence report phrase

A race in the intel-hid ACPI notify handler on affected convertible or detachable systems can double-register the lazy SW_TABLET_MODE input device and later trigger a NULL pointer dereference, causing a local or firmware-mediated denial of service.

## 6. Manual review recommendation

NO MANUAL CHECK NEEDED

The issue is non-network, hardware-specific, race-dependent, and supported impact is DoS only, with no evidence of UAF, OOB access, controlled corruption, information disclosure, or privilege escalation.

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

Patch: platform/x86: intel-hid: Protect ACPI notify handler against recursion
Commit: a6402808e552e44e9c26a9fe8395ac11703d5800
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=a6402808e552e44e9c26a9fe8395ac11703d5800

Commit description:

Since commit e2ffcda ("ACPI: OSL: Allow Notify () handlers to run on
all CPUs") ACPI notify handlers like the intel-hid notify_handler() may
run on multiple CPU cores racing with themselves.

On convertibles and detachables (matched by DMI chassis-type 31 and 32 in
dmi_auto_add_switch[]) the SW_TABLET_MODE input device is registered
lazily from notify_handler() on the first tablet-mode event, via
intel_hid_switches_setup(). When two such events race on different CPUs
both can pass the !priv->switches check and register the priv->switches
input device twice, resulting in a duplicate sysfs entry and a subsequent
NULL pointer dereference.

This is the same class of bug fixed by commit e075c3b ("platform/x86:
intel-vbtn: Protect ACPI notify handler against recursion") for the
sibling intel-vbtn driver.

Protect intel-hid notify_handler() from racing with itself with a mutex
to fix this.

Fixes: e2ffcda ("ACPI: OSL: Allow Notify () handlers to run on all CPUs")
Cc: stable@vger.kernel.org
Signed-off-by: HyeongJun An <sammiee5311@gmail.com>
Link: https://patch.msgid.link/20260605174905.131095-1-sammiee5311@gmail.com
Reviewed-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  drivers/platform/x86/intel/hid.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=a6402808e552e44e9c26a9fe8395ac11703d5800

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

The original Linux kernel CVE announcement for CVE-2026-64603 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64603

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:P/AC:H/PR:N/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: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: 1
  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).