[CVE-2026-98859][MODERATE 7.0] HID: multitouch: stop the release timer from being rearmed on remove [ Upstream

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

CVE: CVE-2026-98859
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: HID: multitouch: stop the release timer from being rearmed on remove [ Upstream
Commit: 1f1bd9a3117f082eb891c0986c4f0e04cd974c9a
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=1f1bd9a3117f082eb891c0986c4f0e04cd974c9a
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98859
Analysis date: Mon, 19 Oct 2026 04:48:37 -0400
ActionableScore: 5
ActionableScore lower bound: 4
Actionable bucket: Actionable Moderate / Strong Important candidate requiring manual review
Manual review required: YES

Summary:
A late HID multitouch report can rearm a timer during device removal, causing the callback to read and modify a freed driver object and potentially crash the kernel, while exploitation beyond denial of service remains unresolved.

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ABOUT THIS REPORT
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The original Linux kernel CVE announcement for CVE-2026-98859 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98859

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-2026-98859	MODERATE	https://www.kernelcve.org/list/?q=CVE-2026-98859 CHECK WITH IMPACT FROM ORIG NN MODERATE | AEGIS IMPACT MODERATE_KPANIC AEGIS_AS=1 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:A/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H';*CWE-416;CWE-362;*CWE-672;Other CVSS 'AV:P/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:H';BEST CVSS score: '7.5';DESCR 'A race in the HID multitouch removal path can rearm release_timer after timer_delete_sync has already returned. The mt_device object is freed after mt_remove completes, but the queued timer can later execute mt_expired_timeout and dereference the released td object. The callback reads td hdev and performs a bit operation on td mt_io_flags, so the issue includes access to and modification of freed memory rather than only a harmless stale timer warning. The most likely impact is a kernel crash and denial of service, while controlled reuse of the freed allocation could potentially affect confidentiality or integrity and requires manual analysis. For the CVSS the PR:N value reflects a malicious attached HID device that can deliver reports and disconnect without holding an account or privilege on the target. The paranoid AV:A interpretation is applicable only where an affected HID transport can be reached over an adjacent connection such as Bluetooth. Typical USB exploitation instead requires physical device access and the race has AC:H because a report must arrive during the narrow teardown window. The issue is not directly reachable over ordinary IP networks or the public Internet. Automated impact decision path. The original SimpleNet classifier selected MODERATE_KPANIC. The primary LLM estimated paranoid CVSS 7.5 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 MODERATE_KPANIC to IMPORTANT because the CVSS score, vector or bug class threshold rule was applied. KP and FD specialist checks stage IMPORTANT to MODERATE_KPANIC because FD false positive review allowed a downgrade. 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 produced a review artifact and its decision was processed by the applicable downgrade and preservation rules. Exact triggered rule markers were INCREASED_TO_HIGH_BASED_ON_GUESSCVSS and DECREASED_TO_MODERATE7_BASED_ON_FALSEPOSCHECKOFDH. The independent weaker Aegis shadow evaluated CVSS 2.0 and ActionableScore 1 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	USB INIT UAF TIMER HARDWARE LINUS KPANIC  KPANIC INCREASED_TO_HIGH_BASED_ON_GUESSCVSS DECREASED_TO_MODERATE7_BASED_ON_FALSEPOSCHECKOFDH	-	-	checked

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

1. ActionableScore

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

2. Signal breakdown

Conservative signals:

* +2 Real UAF. A report can rearm the timer after `timer_delete_sync()`, and the timer subsequently dereferences `td` after devres has freed it.
* +1 Constrained post-free mutation. `test_and_set_bit_lock()` performs a write-like bit operation through the dangling `td` pointer, and the callback can consume `td->hdev` in further input traversal.
* +1 Firmware or peripheral-mediated external influence. An attached HID device controls report delivery and can participate in transport disconnection without a host account.
* +1 Realistic kernel crash. The timer callback accesses a freed driver object and may follow a stale `hdev` pointer.
* -1 Hard teardown race. A report must arrive after `timer_delete_sync()` returns but before report delivery is stopped.

Paranoid-only signal:

* +1 Attacker-influenced lifetime sequence. A malicious peripheral can defensibly be considered able to coordinate report delivery, timer rearming, and disconnection, although reliable repetition and heap placement are not demonstrated.

Important non-awarded signals:

* Controlled reclaim, attacker-shaped replacement contents, arbitrary write, callback hijacking, disclosure, and privilege escalation are not demonstrated.
* No extra availability point was awarded because it would duplicate the same kernel-crash consequence.
* No confidentiality or integrity consequence was awarded merely from theoretical slab reuse.
* No repeated release or refcount signal exists. The bug performs a stale timer callback, not a second `put`, `free`, or refcount mutation.
* FLOOR 5 was not applied. The paranoid score reaches 5 through arithmetic.
* The B3, B4, B5-R, V32, V33, and V34 profiles do not apply.

3. Reachability analysis

A malicious or malfunctioning HID multitouch peripheral can deliver the late report that rearms the timer. Removal can follow physical USB disconnection or an adjacent HID transport disconnection such as Bluetooth, so host-administrator privilege and host UID 0 are not required for that device-originated model.

The affected device must use the sticky-finger timer path. The trigger also requires a narrow teardown interleaving, which limits reliability. No ordinary IP-network trigger is established. No user-namespace or network-namespace capability participates in the complete trigger, and a local software-emulated HID path is not established by the supplied evidence.

4. Primitive and severity interpretation

The exact primitive is an asynchronous timer use-after-free of `struct mt_device`. The object is a structured driver context, but the stale address is fixed and no controlled reclaim is shown. The stale callback reads `td->hdev`, modifies `td->mt_io_flags`, and may call `mt_release_contacts()`, which traverses input state.

This is broader than a read-only stale-pointer fault because a concrete post-free bit mutation occurs. It remains CLASS_B rather than CLASS_A because the attacker cannot currently select the overwritten address or value, control a replacement object, or direct an arbitrary kernel operation.

The demonstrated consequence is kernel memory access after lifetime end with a plausible crash or host DoS. Exploitation beyond DoS remains unresolved rather than proven. ImportantCandidate is YES because the post-free mutation and pointer traversal deserve Important-versus-Moderate review. AutoDowngradeAllowed is NO because automatically reducing the issue to a harmless teardown crash would discard this unresolved corruption primitive.

5. One-sentence report phrase

A late HID multitouch report can rearm a timer during device removal, causing the callback to read and modify a freed driver object and potentially crash the kernel, while exploitation beyond denial of service remains unresolved.

6. Manual review recommendation

MANUAL CHECK REQUIRED

The patch establishes a real UAF with a concrete post-free bit mutation and subsequent stale pointer consumption, although controlled reclaim or privilege escalation is not demonstrated.

7. Call-site confidence

Call-site confidence: high

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

Patch: HID: multitouch: stop the release timer from being rearmed on remove [ Upstream
Commit: 1f1bd9a3117f082eb891c0986c4f0e04cd974c9a
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=1f1bd9a3117f082eb891c0986c4f0e04cd974c9a

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=1f1bd9a3117f082eb891c0986c4f0e04cd974c9a

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

The original Linux kernel CVE announcement for CVE-2026-98859 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98859

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:H/PR:N/UI:N/S:U/C:L/I:L/A:H
  The Best / paranoid CVSS vector: AV:A/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H
  The Best / paranoid CVSS score: 7.5

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).