[CVE-2026-64271][IMPORTANT] Input: touchwin - reset the packet index on every complete packet

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

CVE: CVE-2026-64271
Priority: IMPORTANT
AL-KERNEL base severity: IMPORTANT
KPANIC flag: YES
Patch: Input: touchwin - reset the packet index on every complete packet
Commit: ed9b66905407eb3d02df1aaeed82eb7a7f0eb508
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=ed9b66905407eb3d02df1aaeed82eb7a7f0eb508
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64271
Analysis date: Sat, 25 Jul 2026 12:08:51 -0400
ActionableScore: 7
ActionableScore lower bound: 5
Actionable bucket: Strong Important candidate / Actionable Moderate at minimum
Manual review required: YES

Summary:
A malicious Touchwin-compatible serial touchscreen can prevent packet index reset and drive an unbounded attacker-controlled heap out-of-bounds write in the kernel input driver, requiring physical or device-path control and warranting manual review for possible exploitation beyond DoS.

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

The original Linux kernel CVE announcement for CVE-2026-64271 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64271

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.

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

CVE-2026-64271	IMPORTANT	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-122;*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 heap out of bounds write exists in the Touchwin serial touchscreen driver because tw_interrupt stores non zero device bytes into a fixed three byte packet buffer and only reset the packet index when the second and third Y bytes match. A malicious, malfunctioning, or counterfeit Touchwin compatible peripheral can keep sending packets with mismatching Y bytes so the index is not reset and later bytes are written past tw data into the heap allocated driver object and potentially adjacent kernel heap memory. For the CVSS the PR:N means the attacker does not need privileges on the host if they control the attached peripheral or the serial input source. The issue is not network reachable in the normal deployment model and requires physical or hardware level access to the affected input device path. Impact is at least denial of service via kernel memory corruption and crash. In the paranoid interpretation, the attacker controlled heap out of bounds write can justify high confidentiality and integrity impact because kernel heap corruption may be exploitable beyond DoS.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 7)  SKIP CVE-2026-64271 UNKNOWN SKIP No affected files built, so skip this CVE NO  - - unknown 	MAYBE	WRITE OOB HARDWARE LINUS KPANIC PACKET  KPANIC INCREASED_TO_HIGH_BASED_ON_ACTIONABLESCOREHIGHEREQTHAN7	-	-	checked

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

ActionableScore=7
ActionableScoreLower=5

## 1. ActionableScore

* Conservative score: 5
* Paranoid score: 7
* Final recommended bucket: **Strong Important candidate / Actionable Moderate at minimum**::

## 2. Signal breakdown

Conservative signals:

* Firmware-mediated external influence: +1. The input stream is controlled by a malicious, malfunctioning, or counterfeit Touchwin-compatible peripheral.
* Memory corruption, strong corruption primitive: +2. The bug is an unbounded heap out-of-bounds write into `struct tw` and potentially adjacent heap memory.
* Privilege escalation plausible: +2. The overwrite is attacker-chosen one byte at a time, so kernel heap corruption may be exploitable beyond DoS, although no concrete exploit chain is shown.
* Reliable kernel crash / strong DoS: +1. Heap corruption from interrupt context can realistically crash the kernel.
* Privileged kernel/device-management memory corruption path: +1. The corruption occurs inside a kernel input driver fed by device-controlled bytes.
* Physical-only or rare hardware-only condition: -2. Realistic triggering requires control of the attached serial touchscreen or compatible serio input path.

Paranoid additions:

* Confidentiality impact plausible: +1. If heap corruption is shaped successfully, information exposure is technically plausible.
* Integrity impact plausible: +1. Successful exploitation of the heap overwrite could modify kernel objects or control-relevant state.

## 3. Reachability analysis

The attacker needs control over the Touchwin-compatible serial touchscreen data stream, typically via a malicious or counterfeit physical peripheral. This is not network reachable in the normal deployment model. No local Linux user privilege is required if the attacker controls the device input path, but physical or hardware-level access is required. The affected driver is not a broad default exposure path and depends on the specific touchscreen hardware or serio configuration. Call-site confidence: high, because the vulnerable interrupt handler and fixed-size buffer write are present in the provided patch.

## 4. Severity interpretation

This is not an ordinary Moderate device quirk because the patch describes an attacker-chosen, unbounded heap out-of-bounds write. The realistic exposure is limited by physical or rare hardware requirements, which prevents treating it like a broadly reachable kernel LPE. However, the primitive itself is strong enough that it should not be auto-closed as low-risk DoS. Conservative handling is Actionable Moderate. Paranoid handling is a Strong Important candidate due to kernel heap corruption with plausible confidentiality and integrity impact.

## 5. One-sentence report phrase

A malicious Touchwin-compatible serial touchscreen can prevent packet index reset and drive an unbounded attacker-controlled heap out-of-bounds write in the kernel input driver, requiring physical or device-path control and warranting manual review for possible exploitation beyond DoS.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

Reason: the bug is an attacker-controlled kernel heap out-of-bounds write, even though realistic reachability is limited to physical or device-mediated attack scenarios.

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

Patch: Input: touchwin - reset the packet index on every complete packet
Commit: ed9b66905407eb3d02df1aaeed82eb7a7f0eb508
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=ed9b66905407eb3d02df1aaeed82eb7a7f0eb508

Commit description:

tw_interrupt() accumulates each non-zero serial byte into a fixed
three-byte buffer with a running index that is only reset once a full
packet has been received *and* the device's two Y bytes agree:

	tw->data[tw->idx++] = data;
	if (tw->idx == TW_LENGTH && tw->data[1] == tw->data[2]) {
		...
		tw->idx = 0;
	}

The reset is gated on tw->data[1] == tw->data[2], a value the device
controls.  A malicious, malfunctioning or counterfeit Touchwindow
peripheral can stream non-zero bytes whose 2nd and 3rd bytes differ: the
index reaches TW_LENGTH without the equality holding, is never reset, and
keeps growing, so tw->data[tw->idx++] walks off the end of the three-byte
array and the rest of the heap-allocated struct tw, one attacker-chosen
byte at a time -- an unbounded, device-driven heap out-of-bounds write.

Reset the index on every completed packet and report an event only when
the two Y bytes match, like the other serio touchscreen drivers do.

Fixes: 11ea317 ("Input: add driver for Touchwin serial touchscreens")
Cc: stable@vger.kernel.org
Signed-off-by: Bryam Vargas <hexlabsecurity@proton.me>
Link: https://patch.msgid.link/20260613-b4-disp-69921bfd-v1-1-82c036899959@proton.me
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  drivers/input/touchscreen/touchwin.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=ed9b66905407eb3d02df1aaeed82eb7a7f0eb508

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

The original Linux kernel CVE announcement for CVE-2026-64271 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64271

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: 5
  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: 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).