[CVE-2026-80574][MODERATE 7.0] Input: focaltech - fix array out-of-bounds in focaltech_process_rel_packet

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

CVE: CVE-2026-80574
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: Input: focaltech - fix array out-of-bounds in focaltech_process_rel_packet
Commit: 063b4c6a6f3fc01bca085c442000c9c100fdbd93
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=063b4c6a6f3fc01bca085c442000c9c100fdbd93
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80574
Analysis date: Wed, 26 Aug 2026 11:31:37 -0400
ActionableScore: 6
ActionableScore lower bound: 4
Actionable bucket: Actionable Moderate at minimum
Manual review required: YES

Summary:
A malformed FocalTech PS/2 packet can cause `focaltech_process_rel_packet()` to write before the `state->fingers` array, resulting in kernel memory corruption with realistic DoS impact and a paranoid privilege-escalation concern under hardware-level attacker control.

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ABOUT THIS REPORT
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The original Linux kernel CVE announcement for CVE-2026-80574 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80574

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.

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AL-KERNEL CLASSIFICATION RESULT
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CVE-2026-80574	MODERATE	CHECK WITH IMPACT FROM ORIG NN IMPORTANT	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:P/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H';*CWE-787;CWE-129;*CWE-20;Other CVSS 'AV:P/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:H';BEST CVSS score: '6.8';DESCR 'A malformed FocalTech PS/2 relative packet with finger index 0 can make focaltech_process_rel_packet compute an array index of -1 and write before state fingers. This is a kernel out of bounds write in the input driver rather than a pure warning or resource leak. For the CVSS the PR:N reflects that a malicious physical device can send the crafted packet without a local user account. The issue is not network reachable and normally requires physical or hardware level access to the affected touchpad path. Impact is at least local denial of service via kernel memory corruption and in the paranoid case may allow confidentiality and integrity impact if the out of bounds write can corrupt security relevant kernel state.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate at minimum (with actual score 5)	YES	WRITE OOB DANGER SIMPLEFIX IMPROVEONLY LINUS PACKET  DECREASED_TO_MODERATE70_BASED_ON_ACTIONABLESCORELOWERTHAN6 DECREASED_TO_MODERATEREG_BASED_ON_FALSEPOSCHECKOFKP	NO	NO	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=6
ActionableScoreLower=4

## 1. ActionableScore

* Conservative score: 4
* Paranoid score: 6
* Final recommended bucket: **Actionable Moderate at minimum**

## 2. Signal breakdown

* Firmware/device-mediated external influence: +1
  A malformed FocalTech PS/2 packet can be supplied by the touchpad device path or a malicious compatible device.

* Generic memory corruption, strong primitive: +2
  The bug can write to `state->fingers[-1]`, which is an explicit kernel out-of-bounds write.

* Privileged kernel/device-management memory corruption path: +1
  The corruption occurs inside a kernel input driver processing hardware-fed packets.

* Reliable kernel crash / strong DoS: +1
  An OOB write in kernel memory can realistically crash the kernel, even if the patch does not show a specific panic trace.

* Integrity impact plausible: +1
  The write is outside the intended array and may corrupt adjacent driver state.

* Weak LPE concern, paranoid only: +1
  Privilege escalation is not demonstrated, but kernel OOB write into adjacent state is enough to require manual review.

* Confidentiality impact plausible, paranoid only: +1
  Not shown directly, but included in the paranoid score because adjacent kernel-state corruption may potentially influence later behavior.

* Physical-only or rare hardware-only condition: -2
  This is not network reachable and normally requires physical or hardware-level influence over the affected PS/2 touchpad packet stream.

## 3. Reachability analysis

The realistic trigger is a malformed FocalTech PS/2 relative packet with finger index 0. This is not reachable over the network and is not a normal local syscall or namespace-controlled interface. A local unprivileged user generally cannot trigger it unless they can influence the physical input device, emulate the hardware path, or operate in a test environment with injected PS/2 packets.

Namespaces and containers do not materially lower the privilege requirement because the vulnerable path is below normal container-visible input APIs. The affected code is relevant only on systems using the FocalTech PS/2 protocol extension, so exposure is hardware-dependent rather than broad default network exposure.

## 4. Severity interpretation

This is stronger than an ordinary Moderate correctness bug because the patch fixes an explicit kernel OOB write. However, it is not a clear Important-class issue in the conservative view because the trigger is physical or device-mediated and the overwrite target appears constrained to adjacent driver state. Theoretical memory-corruption risk exists, including possible privilege-escalation concern, but realistic exploitation evidence is limited by the hardware path and lack of a demonstrated reclaim, arbitrary write, callback overwrite, or type-confusion chain.

## 5. One-sentence report phrase

A malformed FocalTech PS/2 packet can cause `focaltech_process_rel_packet()` to write before the `state->fingers` array, resulting in kernel memory corruption with realistic DoS impact and a paranoid privilege-escalation concern under hardware-level attacker control.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

Reason: this is an explicit kernel out-of-bounds write, even though reachability is physical or hardware-mediated and practical exploitation beyond DoS is not demonstrated.

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

Patch: Input: focaltech - fix array out-of-bounds in focaltech_process_rel_packet
Commit: 063b4c6a6f3fc01bca085c442000c9c100fdbd93
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=063b4c6a6f3fc01bca085c442000c9c100fdbd93

Commit description:

Make finger2 (and also finger1) unsigned, so that if the finger index in
the packet is 0 then subtracting 1 creates an array index which overflows
above the existing check for FOC_MAX_FINGERS, as the existing comment says
it should, instead of writing to state->fingers[-1].

Fixes: 05be1d0 ("Input: psmouse - support for the FocalTech PS/2 protocol extensions")
Signed-off-by: Richard Davies <richard@arachsys.com>
Link: https://patch.msgid.link/20260701190932.14960-1-richard@arachsys.com
Cc: stable@vger.kernel.org
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  drivers/input/mouse/focaltech.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=063b4c6a6f3fc01bca085c442000c9c100fdbd93

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

The original Linux kernel CVE announcement for CVE-2026-80574 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80574

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:L/PR:N/UI:N/S:U/C:L/I:L/A:H
  The Best / paranoid CVSS vector: AV:P/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
  The Best / paranoid CVSS score: 6.8

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: 4
  Paranoid ActionableScore: 6

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 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).