[CVE-2026-98286][MODERATE REGULAR] drop_monitor: use timer_shutdown_sync() to prevent timer rearming during teardown [ Upstream

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

CVE: CVE-2026-98286
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: drop_monitor: use timer_shutdown_sync() to prevent timer rearming during teardown [ Upstream
Commit: 9616b0c67fbd8cc0b49de7b26cdf2ab33747c80e
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=9616b0c67fbd8cc0b49de7b26cdf2ab33747c80e
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98286
Analysis date: Sat, 10 Oct 2026 18:53:17 -0400
ActionableScore: 0
ActionableScore lower bound: unknown
Actionable bucket: Ordinary Moderate
Manual review required: NO

Summary:
No one-sentence report phrase was found.

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

The original Linux kernel CVE announcement for CVE-2026-98286 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98286

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 REGULAR
Manual review required: NO

A detailed explanation of the methodology and priority rules is included
at the end of this message.

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

CVE-2026-98286	MODERATE	https://www.kernelcve.org/list/?q=CVE-2026-98286 CHECK WITH IMPACT FROM ORIG NN MODERATE | AEGIS IMPACT MODERATE_KPANIC AEGIS_AS=0 LEGACY=MODERATE RESULT=DIFF (independent Legacy and Aegis differ; FINAL: MODERATE, Aegis: MODERATE_KPANIC)	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:H/PR:H/UI:N/S:U/C:L/I:L/A:H';*CWE-416;CWE-362;CWE-667;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '5.2';DESCR 'A race in drop_monitor teardown can allow dm_alert_work to rearm a per CPU send_timer after timer_delete_sync has already returned. If the work is then cancelled and the module reference is released, the active timer may later invoke sched_send_work from unloaded module memory. This creates a use after free condition and can cause a kernel panic. For the CVSS the PR:H is selected because reliable triggering normally requires administrative control over drop_monitor teardown and module unloading. AC:H is selected because exploitation also depends on a narrow race window and a memory allocation failure while the worker is resetting per CPU state. The issue is not directly network reachable because packet traffic alone cannot perform the required teardown or unload operation. Impact is at least a local denial of service. In the paranoid case limited confidentiality or integrity impact is considered because execution can continue through a stale timer callback after module memory has been freed, although a reliable privilege escalation primitive is not established.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 0)	MAYBE	REMOTE INIT UAF TIMER HARDWARE LINUS  DECREASED_TO_MODERATE_REGULAR_FROM_MODERATE7_BASED_ON_GUESSCVSS_AND_CIANNH	-	-	checked

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

ActionableScore=0
PrimitiveClass=CLASS_B
RealUAF=YES
HostAdminRequired=YES
NamespaceScopedPrivilege=NO
ImportantCandidate=NO
ManualReview=RECOMMENDED
AutoDowngradeAllowed=YES
RequiresHostUID0=NO
AuthorizationDecisionBypass=NO
ProtectedResourceImpact=NONE
B4PendingReview=NO
B4PendingConfirmed=NO

1. ActionableScore

* Raw conservative score: 0
* Conservative score: 0
* Raw paranoid score: 0
* Paranoid score: 0
* No floor or cap was applied. The real-UAF floors do not apply because host-admin-equivalent module-unload privilege is established and the stale use is a constrained per-CPU teardown path without demonstrated reuse leverage.
* Final recommended bucket: **Ordinary Moderate**::

2. Signal breakdown

Positive signals:

* +2 Real UAF / lifetime violation. A running worker can rearm `send_timer` after `timer_delete_sync()` returns. The timer remains registered after module teardown and can be consumed after its owning module storage and callback code have been unloaded.
* +1 Reliable kernel crash / strong DoS. The commit directly identifies a kernel panic when the stale timer invokes `sched_send_work()` from unloaded module memory.

Negative signals:

* -2 Proven host-admin-equivalent requirement. Completing the documented sequence requires unloading the kernel module, which requires effective `CAP_SYS_MODULE` authority in the initial user namespace.
* -1 Hard one-shot teardown race. The sequence requires concurrent timer teardown and worker execution, an allocation failure during per-CPU state reset, successful timer rearming in the relevant window, and subsequent module unload.

Important non-awarded signals:

* No controlled reclaim or attacker-shaped reuse is demonstrated.
* No arbitrary or directed kernel write is demonstrated.
* No callback-pointer influence is awarded. Callback invocation is concrete, but attacker control over the callback value or replacement module memory is not established.
* No structured stale-object leverage is awarded because this is fixed per-CPU/module teardown storage with no demonstrated attacker-controlled replacement.
* No weak or strong LPE point is awarded merely from execution reaching unloaded module text.
* No extra Availability point is awarded because it would duplicate the kernel-panic consequence.
* No Confidentiality or Integrity point is awarded.
* No remote-reachability point is awarded. Packet activity alone cannot complete teardown and module unload.
* No repeated release/refcount signal exists. There is no first lifetime release followed by a second refcount or release mutation through the exact same dangling reference.
* B5-R does not apply because no heap OOB write exists.
* B3-PENDING does not apply because no shared-backing write exists.
* B4-PENDING does not apply because no authorization decision is bypassed.

3. Reachability analysis

The complete demonstrated trigger is local and host-administrative. Starting or stopping drop monitoring may involve privileged netlink control, but the security-relevant terminal stage additionally requires unloading the module while a rearmed timer remains active. Kernel module unloading is governed by host-level `CAP_SYS_MODULE`, not an attacker-created user or network namespace.

Numeric UID 0 is not intrinsically required because Linux uses a capability check, but the required effective capability is host-admin-equivalent. The complete chain is therefore not namespace scoped.

Network packets may exercise drop-monitor activity, and memory pressure may help produce the allocation failure, but neither gives a remote or ordinary local attacker the authority to stop monitoring and unload the module. No special hardware is required. The race is materially constrained because it combines a one-time teardown transition, concurrent worker execution, allocation failure, post-delete rearming, and module unload.

4. Primitive and severity interpretation

The exact primitive is an asynchronous post-teardown timer UAF. `timer_delete_sync()` waits for a running callback but does not permanently reject a later `mod_timer()`. A concurrent worker can therefore rearm the timer after deletion. The timer wheel subsequently consumes stale per-CPU timer state and dispatches a callback whose module code has been unloaded.

This is fixed stale per-CPU/module storage rather than an attacker-shaped active structured object. It is broader than a plain NULL dereference because execution reaches a stale timer callback after lifetime termination, so `PrimitiveClass=CLASS_B` and `RealUAF=YES` are appropriate. However, the demonstrated consequence is kernel panic, with no controlled reclaim, callback replacement, post-free payload control, arbitrary read/write, repeated refcount mutation, or security-boundary bypass.

The theoretical worst case includes reuse of freed module memory before the timer fires, but the supplied evidence does not establish attacker control over that reuse or a useful control-flow target. It therefore does not support Class A or an Important-preserving score.

`ImportantCandidate=NO` because the complete documented chain is host-admin gated and the UAF is a constrained teardown callback with crash-only evidence. `AutoDowngradeAllowed=YES` because no independently useful exploitation primitive remains unresolved beyond the stale callback and panic. Operational severity is ordinary Moderate or Low-like despite the technically real UAF.

5. One-sentence report phrase

A drop_monitor teardown race can leave a per-CPU timer armed after module unload and invoke a callback from freed module memory, causing a host-admin-triggered kernel panic without a demonstrated controlled-reuse or privilege-escalation primitive.

6. Manual review recommendation

MANUAL CHECK RECOMMENDED

The UAF and stale callback are concrete, but review is primarily warranted to confirm whether any product-specific automatic module-unload or delegated management path removes the otherwise established host-admin requirement.

7. Call-site confidence

Call-site confidence: high

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

Patch: drop_monitor: use timer_shutdown_sync() to prevent timer rearming during teardown [ Upstream
Commit: 9616b0c67fbd8cc0b49de7b26cdf2ab33747c80e
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=9616b0c67fbd8cc0b49de7b26cdf2ab33747c80e

Changed files:
  net/core/drop_monitor.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=9616b0c67fbd8cc0b49de7b26cdf2ab33747c80e

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

The original Linux kernel CVE announcement for CVE-2026-98286 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98286

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:H/PR:H/UI:N/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS vector: AV:L/AC:H/PR:H/UI:N/S:U/C:L/I:L/A:H
  The Best / paranoid CVSS score: 5.2

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: unknown
  Paranoid ActionableScore: 0

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 REGULAR

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).