[CVE-2026-64364][IMPORTANT] HID: multitouch: fix out-of-bounds bit access on mt_io_flags [ Upstream

[CVE-2026-64364][IMPORTANT] HID: multitouch: fix out-of-bounds bit access on mt_io_flags [ Upstream

[AL-KERNEL]

CVE: CVE-2026-64364
Priority: IMPORTANT
AL-KERNEL base severity: IMPORTANT
KPANIC flag: YES
Patch: HID: multitouch: fix out-of-bounds bit access on mt_io_flags [ Upstream
Commit: 12e90656e330ff8bbaf2f29c535fdb8a11cc6f55
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=12e90656e330ff8bbaf2f29c535fdb8a11cc6f55
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64364
Analysis date: Sat, 25 Jul 2026 15:24:34 -0400
ActionableScore: 8
ActionableScore lower bound: 6
Actionable bucket: Strong Important candidate / Actionable Moderate at minimum
Manual review required: YES

Summary:
A malicious USB or Bluetooth HID multitouch device can advertise an excessive contact count and cause out-of-bounds bit writes past `mt_io_flags`, corrupting adjacent kernel HID state and leading to a reliable kernel crash, with worst-case manual-review concern for broader memory-corruption impact.

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ABOUT THIS REPORT
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The original Linux kernel CVE announcement for CVE-2026-64364 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64364

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: IMPORTANT
Manual review required: YES

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-2026-64364	IMPORTANT	CHECK WITH IMPACT FROM ORIG NN NONE	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:A/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H';*CWE-787;CWE-129;CWE-119;Other CVSS 'AV:A/AC:L/PR:N/UI:R/S:U/C:L/I:L/A:H';BEST CVSS score: '8';DESCR 'HID multitouch used mt_io_flags as a per slot bitmap even though it is only a single unsigned long. A malicious USB or Bluetooth HID multitouch device can advertise a large ContactCountMaximum and then drive slot indexes beyond BITS_PER_LONG, causing set_bit and clear_bit to modify adjacent fields in struct mt_device. The easiest observed failure is through the sticky fingers release timer, where clearing slots around 250 can corrupt a list head and lead to a NULL pointer dereference from timer context. For the CVSS the PR:N is used because the attacker does not need an account or local privileges on the target, only the ability to present an untrusted HID device over USB or Bluetooth. UI:R is used because the device normally must be attached, paired, or accepted by the victim or environment. The issue is not Internet reachable, but it is reachable from physical or adjacent device access. Impact is at least denial of service via kernel panic, and worst case may include confidentiality and integrity impact because the primitive is an out of bounds bit write into adjacent kernel structure fields.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 8)  SKIP CVE-2026-64364 UNKNOWN SKIP The Fixes patch not applied yet, so unlikely that actual: 46f781e0d151844589dc2125c8cce3300546f92a YES  NO NO unknown 	MAYBE	WRITE KASAN OOB NULLPTR USB NOMEMCHK HARDWARE LINUS KPANIC  KPANIC INCREASED_TO_MODERATE_FROM_LOW_BASED_ON_GUESSCVSS KPANIC INCREASED_TO_HIGH_BASED_ON_ACTIONABLESCOREHIGHEREQTHAN7	-	-	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=8
ActionableScoreLower=6

## 1. ActionableScore

* Conservative score: 6
* Paranoid score: 8
* Final recommended bucket: **Strong Important candidate / Actionable Moderate at minimum**::

## 2. Signal breakdown

Triggered signals:

* Firmware or external device mediated influence: +1
  The input is controlled by an untrusted USB or Bluetooth HID multitouch device.
* Generic memory corruption, strong primitive: +2
  `set_bit()` and `clear_bit()` operate out of bounds past a single `unsigned long` and corrupt adjacent fields in `struct mt_device`.
* Weak LPE concern: +1
  The demonstrated failure is a crash, but the primitive is an OOB bit write into kernel object fields, so limited C/I or LPE concern is technically plausible.
* Reliable kernel crash / strong DoS: +1
  The commit describes a reproducible panic from timer softirq context via corrupted list state and NULL dereference.
* Confidentiality impact plausible: +1
  Conservative lower scoring treats this as limited or uncertain, but paranoid scoring allows C impact because adjacent kernel object corruption is present.
* Integrity impact plausible: +1
  The overwrite can modify adjacent kernel structure fields, although payload and target control are constrained.
* Broad/default/common subsystem: +1
  HID multitouch support is commonly enabled on desktop, laptop, and mobile-oriented kernels.
* Privileged kernel/device-management memory corruption path: +1
  The corruption occurs inside a trusted kernel HID driver from externally supplied device descriptors/events.
* Constrained primitive / no arbitrary payload: -1
  The write is bit set/clear indexed by slot number, not an arbitrary attacker-chosen write payload.

Conservative score is kept at 6 because the demonstrated practical impact is kernel panic, while confidentiality, integrity, and LPE remain plausible but not proven. Paranoid score is 8 because this is real kernel memory corruption reachable from an untrusted peripheral.

Call-site confidence: high. The patch shows the affected call sites in `mt_process_slot()`, `mt_release_pending_palms()`, `mt_release_contacts()`, and the timer path.

## 3. Reachability analysis

The bug can be triggered by a malicious USB or Bluetooth HID multitouch device that advertises a large `ContactCountMaximum`, causing slot indexes larger than `BITS_PER_LONG`. No local user account or local privileges are required on the victim system.

This is not Internet remote. It requires physical USB attachment or Bluetooth proximity/pairing/acceptance, so it is best treated as adjacent or external-device reachable. Namespaces and containers do not meaningfully reduce the issue because the attack enters through the host HID stack.

The affected path is realistic on systems that accept HID multitouch devices and have the driver enabled. The most concrete trigger path is the sticky-fingers release timer, where clearing many slots corrupts adjacent list metadata and leads to panic.

## 4. Severity interpretation

This is not an ordinary Moderate resource issue. It is at least an actionable Moderate and a strong Important candidate because the patch fixes an out-of-bounds bit write in kernel memory, not just a validation warning or bookkeeping bug.

Realistically demonstrated impact is reliable local host DoS via kernel panic from an untrusted HID device. Theoretical worst-case impact is higher because the primitive corrupts adjacent members of `struct mt_device`, but the overwrite is constrained to bit operations and the provided evidence does not show arbitrary write, controlled object replacement, or a working LPE chain.

## 5. One-sentence report phrase

A malicious USB or Bluetooth HID multitouch device can advertise an excessive contact count and cause out-of-bounds bit writes past `mt_io_flags`, corrupting adjacent kernel HID state and leading to a reliable kernel crash, with worst-case manual-review concern for broader memory-corruption impact.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

Reason: this is concrete kernel memory corruption reachable from an untrusted external device, with a demonstrated panic and plausible but unproven confidentiality, integrity, or privilege-escalation implications.

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

Patch: HID: multitouch: fix out-of-bounds bit access on mt_io_flags [ Upstream
Commit: 12e90656e330ff8bbaf2f29c535fdb8a11cc6f55
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=12e90656e330ff8bbaf2f29c535fdb8a11cc6f55

Changed files:
  drivers/hid/hid-multitouch.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=12e90656e330ff8bbaf2f29c535fdb8a11cc6f55

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

The original Linux kernel CVE announcement for CVE-2026-64364 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64364

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:A/AC:L/PR:N/UI:R/S:U/C:L/I:L/A:H
  The Best / paranoid CVSS vector: AV:A/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
  The Best / paranoid CVSS score: 8

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: 6
  Paranoid ActionableScore: 8

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: IMPORTANT
KPANIC detected for this report: YES
Published priority for this report (same as in Subject): IMPORTANT

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).