[CVE-2026-98499][MODERATE 7.0] HID: wacom: fix OOB read in wacom_wac_pen_serial_enforce()

[CVE-2026-98499][MODERATE 7.0] HID: wacom: fix OOB read in wacom_wac_pen_serial_enforce()

[AL-KERNEL]

CVE: CVE-2026-98499
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: HID: wacom: fix OOB read in wacom_wac_pen_serial_enforce()
Commit: 9aa62f967b6a4bb30aa3b778e02c8a5ca6bcde51
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=9aa62f967b6a4bb30aa3b778e02c8a5ca6bcde51
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98499
Analysis date: Sat, 24 Oct 2026 11:21:33 -0400
ActionableScore: 5
ActionableScore lower bound: 4
Actionable bucket: Actionable Moderate / Strong Important candidate requiring manual review
Manual review required: YES

Summary:
A low-privilege UHID actor can induce an attacker-indexed report OOB read whose extracted kernel value is exposed through an MSC_SERIAL input event.

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

The original Linux kernel CVE announcement for CVE-2026-98499 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98499

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.

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

CVE-2026-98499	MODERATE	https://www.kernelcve.org/list/?q=CVE-2026-98499 CHECK WITH IMPACT FROM ORIG NN LOW | AEGIS IMPACT MODERATE_KPANIC AEGIS_AS=2 LEGACY=MODERATE_KPANIC RESULT=SAME (final reconciliation agrees; DECISION: both MODERATE_KPANIC)	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:H';CWE-125;CWE-130;*CWE-20;Other CVSS 'AV:L/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:L';BEST CVSS score: '7.1';DESCR 'An inconsistent Wacom HID descriptor can declare more usages than the report count reserves, causing wacom_wac_pen_serial_enforce to calculate an attacker influenced bit offset beyond the received report and pass it to hid_field_extract. The demonstrated descriptor reads about 12 KB beyond a two byte report, and the extracted value can reach userspace as an MSC_SERIAL event, establishing a kernel memory disclosure primitive. For the CVSS the PR:L value reflects that reliable software triggering and collection of the leaked event normally require a local process with access to UHID and the relevant input event interface. Integrity impact is not assigned because the code only reads memory. Availability impact is plausible if a selected offset reaches inaccessible memory and faults, although the supplied evidence directly confirms a KASAN OOB read rather than a production kernel panic. Automated impact decision path. The original SimpleNet classifier selected LOW. The primary LLM estimated paranoid CVSS 7.1 and the production ActionableScore returned 5 with recommendation Actionable Moderate / Strong Important candidate requiring manual review. The production rules then evaluated CVSS thresholds and ActionableScore thresholds. Recorded rule transitions were CVSS and initial triage stage LOW to MODERATE_KPANIC because the ActionableScore threshold rule was applied. The legacy KP specialist produced a review artifact and its decision was processed by the applicable KP rules. The legacy FD or DH downgrade specialist has no review artifact for this run. Exact triggered rule markers were INCREASED_TO_MODERATE7_FROM_LOW_BASED_ON_GUESSCVSS_AND_ACTIONABLESCOREHIGHER4. The independent weaker Aegis shadow evaluated CVSS 2.5 and ActionableScore 2 with primitive class CLASS_B and manual review REQUIRED. Its independently reconciled impact was MODERATE_KPANIC. The shadow agreed with the final production impact and aggregation did not change that impact. The final reported impact is MODERATE_KPANIC.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate / Strong Important candidate requiring manual review (with actual score 5)	MAYBE	KASAN OOB USB LINUS  KPANIC INCREASED_TO_MODERATE7_FROM_LOW_BASED_ON_GUESSCVSS_AND_ACTIONABLESCOREHIGHER4	-	-	checked

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

ActionableScore=5
ActionableScoreLower=4
PrimitiveClass=CLASS_B
RealUAF=NO
HostAdminRequired=NO
NamespaceScopedPrivilege=UNKNOWN
ImportantCandidate=YES
ManualReview=REQUIRED
AutoDowngradeAllowed=NO
RequiresHostUID0=NO
AuthorizationDecisionBypass=NO
ProtectedResourceImpact=NONE
B4PendingReview=NO
B4PendingConfirmed=NO

1. ActionableScore

* Raw base score: 4.
* Conservative score: 4; no floor or cap applied.
* Raw paranoid score: 5.
* Paranoid score: 5; no floor or cap applied.
* Final recommended bucket: **Actionable Moderate / Strong Important candidate requiring manual review**::

2. Signal breakdown

* +1 real attacker-influenced heap/report OOB read: `maxusage` drives an offset about 12 KB beyond a two-byte report.
* +1 confidentiality: the extracted value is stored as the pen serial and can be emitted to userspace as `MSC_SERIAL`.
* +1 practical chain: malformed UHID descriptor → short report → OOB extraction → input event output is explicitly established.
* +1 local below-host-admin trigger: supplied evidence grounds a low-privilege process with UHID and input-event access; host UID 0 is not required.
* Paranoid +1 plausible kernel fault: an attacker-selected offset may reach inaccessible memory, although only a KASAN OOB read—not a production panic—is demonstrated.
* No privilege penalty: host-admin-equivalent privilege is disproven, but the exact device-node permission model varies.
* No arbitrary-address read, write, UAF, integrity impact, LPE, or reliable production crash is shown.
* NEW52/B5-R and NEW53/B3-PENDING do not apply: this is a read, not a retry-accumulated or shared-backing write.
* Authorization/B4 profiles do not apply because no DENY-to-ALLOW guard is involved.

3. Reachability analysis

A local process able to create a UHID device and read the resulting input event can supply both the inconsistent descriptor and short report. The supplied low-privilege characterization supports below-host-admin reachability, but does not establish namespace-scoped capabilities. No physical Wacom hardware, race, boot option, or retry sequence is required.

4. Primitive and severity reading

The primitive is a user-visible, attacker-indexed OOB kernel read, not memory corruption or UAF. The demonstrated disclosure is constrained to values extracted through HID field semantics; arbitrary kernel addressing or high-volume disclosure is unproven. It remains CLASS_B and an Important candidate because actual kernel bytes cross to userspace and the practical disclosure scope needs review. Auto-downgrade is unsafe despite the absence of write or LPE.

5. One-sentence report phrase

A low-privilege UHID actor can induce an attacker-indexed report OOB read whose extracted kernel value is exposed through an MSC_SERIAL input event.

6. Manual review advice

MANUAL CHECK REQUIRED

Confirm extract width, repeatability, allocator layout, event visibility, and product-specific `/dev/uhid` permissions.

7. Call-site confidence

Call-site confidence: high

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

Patch: HID: wacom: fix OOB read in wacom_wac_pen_serial_enforce()
Commit: 9aa62f967b6a4bb30aa3b778e02c8a5ca6bcde51
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=9aa62f967b6a4bb30aa3b778e02c8a5ca6bcde51

Commit description:

The 'wacom_wac_pen_serial_enforce()' function may calculate and pass an
invalid offset to hid_field_extract(), resulting in memory reads at
incorrect addresses -- possibly beyond the end of the report.  If a
field in the HID descriptor lists more usages than its Report Count
actually reserves space for, the function's inner 'j' will walk past
the end of the field:

	for (i = 0; i < report->maxfield; i++) {
		for (j = 0; j < report->field[i]->maxusage; j++) {
			...
			value = hid_field_extract(hdev, raw_data + 1,
						  offset + j * size, size);

A descriptor listing 12288 usages against Report Count 1 has the loop
extract the usage at index 12287 from bit offset 98296 -- about 12 KB
past a 2-byte received report.  The value is stored in
wacom_wac->serial[0] and can reach userspace as an MSC_SERIAL event,
making this an information disclosure.

Clamp the loop to field->report_count, the number of value slots the
report holds.  Value slots past the last declared usage are still
scanned; they reuse that usage (HID 1.11, 6.2.2.8).

Verified on v6.12.105 with a UHID reproducer: a 2-byte report from
such a descriptor trips KASAN before the patch and not after it.

Fixes: 8341720 ("HID: wacom: Queue events with missing type/serial data for later processing")
Suggested-by: Jason Gerecke <killertofu@gmail.com>
Cc: stable@vger.kernel.org
Assisted-by: Claude:claude-opus-5
Assisted-by: GLM:glm-5.3
Signed-off-by: Wei Jie Law <98lawweijie@gmail.com>
Reviewed-by: Jason Gerecke <jason.gerecke@wacom.com>
Signed-off-by: Jiri Kosina <jkosina@suse.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  drivers/hid/wacom_sys.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=9aa62f967b6a4bb30aa3b778e02c8a5ca6bcde51

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

The original Linux kernel CVE announcement for CVE-2026-98499 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98499

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:L/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:L
  The Best / paranoid CVSS vector: AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:H
  The Best / paranoid CVSS score: 7.1

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).