[CVE-2026-63916][MODERATE 7.0] HID: wacom: Fix OOB write in wacom_hid_set_device_mode()

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

CVE: CVE-2026-63916
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: HID: wacom: Fix OOB write in wacom_hid_set_device_mode()
Commit: 2add311d99646c9d235b2c44f9c169ba30f5db3a
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=2add311d99646c9d235b2c44f9c169ba30f5db3a
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-63916
Analysis date: Sun, 19 Jul 2026 21:32:41 -0400
ActionableScore: 5
ActionableScore lower bound: 4
Actionable bucket: Actionable Moderate at minimum
Manual review required: YES

Summary:
A crafted Wacom-compatible HID device can place `HID_DG_INPUTMODE` outside field 0 and trigger an out-of-bounds kernel write during device mode setup, leading to at least DoS and requiring manual review for possible memory-corruption impact.

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ABOUT THIS REPORT
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The original Linux kernel CVE announcement for CVE-2026-63916 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-63916

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-2026-63916	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;*CWE-787;*CWE-787;Other CVSS 'AV:P/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:H';BEST CVSS score: '6.8';DESCR 'An out-of-bounds write in the Wacom HID driver can occur because wacom_hid_set_device_mode() assumed that HID_DG_INPUTMODE is always stored in field 0 of the feature report. A crafted HID device can place HID_DG_INPUTMODE in another field while using an inputmode index that is outside field 0 report_count, causing a write past r field 0 value during device mode setup. For the CVSS the PR:N is used for the paranoid score because an attacker does not need an account on the target if they can present a malicious HID device to the system. The issue is not network reachable in the usual deployment model and requires physical device attachment or an equivalent trusted HID injection path. Impact is at least denial of service via kernel memory corruption and in worst case may allow confidentiality or integrity impact due to an OOB write primitive, so manual review is required.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate at minimum (with actual score 5)	YES	WRITE OOB DANGER USB SIMPLEFIX HARDWARE LINUS KPANIC  KPANIC DECREASED_TO_MODERATE70_BASED_ON_ACTIONABLESCORELOWERTHAN7	NO	NO	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=5
ActionableScoreLower=4

## 1. ActionableScore

* Conservative score: 4
* Paranoid score: 5
* Final recommended bucket: **Actionable Moderate at minimum**::

## 2. Signal breakdown

Conservative signals:

* Memory corruption, strong corruption primitive: +2. The patch fixes an actual out-of-bounds write to `r->field[0]->value[hid_data->inputmode_index]`.
* Reliable kernel crash / strong DoS: +1. A crafted HID report layout can corrupt kernel memory during device mode setup and plausibly crash the kernel.
* Privileged kernel/device-management memory corruption path: +1. The corruption happens in a trusted HID driver path while parsing device-provided report metadata.
* Integrity impact plausible: +1. Kernel memory is written out of bounds, although the written value is constrained.
* Availability impact realistic: +1. Kernel memory corruption can realistically cause device failure or host crash.
* Corruption primitive highly constrained: -1. The payload appears fixed to value `2`, and the target is derived from HID report layout rather than an arbitrary write primitive.
* Physical-only or rare hardware-only condition: -2. Realistic triggering requires a malicious or malformed HID/Wacom-compatible device, or an equivalent HID injection path.

Paranoid adjustment:

* Weak LPE concern: +1. The bug is a kernel OOB write with attacker-influenced indexing through HID descriptor layout, so privilege escalation cannot be ruled out without manual review, even though no reliable exploit primitive is demonstrated.

## 3. Reachability analysis

The bug is triggerable by a crafted HID device that reports `HID_DG_INPUTMODE` in a field other than field 0 while making `inputmode_index` exceed `field[0]->report_count`. No local account is required if the attacker can physically attach or emulate such a device, so this is `PR:N` in a physical attack model. It is not network reachable in the ordinary deployment model. Namespaces and containers do not materially reduce the requirement because the vulnerable path is device enumeration and HID driver setup, not a namespace-scoped local syscall API.

Call-site confidence: high. The patch includes the vulnerable write site and the feature mapping source of `inputmode_index`.

## 4. Severity interpretation

This is not an ordinary low-risk validation bug because the commit explicitly describes an OOB write in kernel memory. Realistically, the primitive is constrained: the write value is fixed and exploitation requires malicious HID device influence, so the conservative score remains below Important. Paranoid triage should still treat it as actionable because kernel OOB writes in device parsing paths can sometimes be shaped into more serious corruption than the minimal crash symptom shows.

## 5. One-sentence report phrase

A crafted Wacom-compatible HID device can place `HID_DG_INPUTMODE` outside field 0 and trigger an out-of-bounds kernel write during device mode setup, leading to at least DoS and requiring manual review for possible memory-corruption impact.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

Reason: this is a concrete kernel OOB write primitive, even though physical reachability and constrained payload keep the practical score moderate rather than clearly Important.

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

Patch: HID: wacom: Fix OOB write in wacom_hid_set_device_mode()
Commit: 2add311d99646c9d235b2c44f9c169ba30f5db3a
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=2add311d99646c9d235b2c44f9c169ba30f5db3a

Commit description:

wacom_hid_set_device_mode() currently assumes that the HID_DG_INPUTMODE
usage is always located in the first field (field[0]) of the feature report.
However, a device can specify HID_DG_INPUTMODE in a different field.

If HID_DG_INPUTMODE is in a field other than the first one and the first
field has a report_count smaller than the usage_index of HID_DG_INPUTMODE,
this leads to an out-of-bounds write to r->field[0]->value.

Fix this by storing the field index of HID_DG_INPUTMODE in 'struct
hid_data' during feature mapping.  In wacom_hid_set_device_mode(), use
this stored field index to access the correct field and add bounds
checks to ensure both the field index and the value index are within
valid ranges before writing.

Cc: stable@vger.kernel.org
Fixes: 5ae6e89 ("HID: wacom: implement the finger part of the HID generic handling")
Tested-by: Ping Cheng <ping.cheng@wacom.com>
Reviewed-by: Ping Cheng <ping.cheng@wacom.com>
Signed-off-by: Lee Jones <lee@kernel.org>
Signed-off-by: Benjamin Tissoires <bentiss@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  drivers/hid/wacom_sys.c
  drivers/hid/wacom_wac.h

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=2add311d99646c9d235b2c44f9c169ba30f5db3a

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

The original Linux kernel CVE announcement for CVE-2026-63916 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-63916

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: 5

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: YES
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).