[CVE-2026-98696][MODERATE 7.0] USB: serial: fix driver deregistration order

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

CVE: CVE-2026-98696
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: USB: serial: fix driver deregistration order
Commit: 9b085a06a0a411b0bcdf18b61c3ebf1be1c72ffe
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=9b085a06a0a411b0bcdf18b61c3ebf1be1c72ffe
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98696
Analysis date: Mon, 19 Oct 2026 00:23:39 -0400
ActionableScore: 1
ActionableScore lower bound: unknown
Actionable bucket: Ordinary Moderate
Manual review required: NO

Summary:
Incorrect USB serial driver deregistration ordering can leave I/O active after port data is released, allowing a completion handler to access freed memory and potentially crash the kernel during a host-privileged module unload.

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ABOUT THIS REPORT
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The original Linux kernel CVE announcement for CVE-2026-98696 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98696

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: NO

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
======================================================================

CVE-2026-98696	MODERATE	https://www.kernelcve.org/list/?q=CVE-2026-98696 CHECK WITH IMPACT FROM ORIG NN MODERATE | AEGIS IMPACT MODERATE_KPANIC AEGIS_AS=1 LEGACY=MODERATE_KPANIC RESULT=SAME V39_AEGIS_ONE_STEP_UP=MODERATE->MODERATE_KPANIC (final reconciliation agrees; DECISION: both 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:H/I:H/A:H';*CWE-416;CWE-362;*CWE-672;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:L/I:L/A:H';BEST CVSS score: '6.4';DESCR 'An incorrect USB serial driver deregistration order can leave USB I/O active while serial port drivers are being unbound and their port data is released. A completion handler may then access freed port data, creating a race based use after free that can cause a kernel crash and may potentially affect confidentiality or integrity if the stale object access becomes controllable. For the CVSS the PR:H is selected because reliable triggering normally requires unloading or deregistering the kernel module through root or CAP_SYS_MODULE. AC:H reflects the timing window between an outstanding USB completion and port teardown. The issue is not network reachable. A connected USB device or a local process using the serial port may influence I/O timing, but neither normally controls module removal without additional privileges. Impact is at least a local denial of service via kernel crash and in the worst defensible case may include confidentiality or integrity impact due to the documented use after free. Automated impact decision path. The original SimpleNet classifier selected MODERATE_KPANIC. The primary LLM estimated paranoid CVSS 6.4 and the production ActionableScore returned 1 with recommendation Ordinary Moderate. The production rules then evaluated CVSS thresholds and ActionableScore thresholds. Recorded rule transitions were ActionableScore thresholds stage MODERATE_KPANIC to MODERATE because the ActionableScore threshold rule was applied. final reconciliation stage MODERATE to MODERATE_KPANIC because the cross model evidence reconciliation rule was applied. The legacy KP specialist has no review artifact for this run. The legacy FD or DH downgrade specialist has no review artifact for this run. Exact triggered rule markers were DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN4 and V39_AEGIS_ONE_STEP_UP and MANUAL_REVIEW_REQUIRED. The independent weaker Aegis shadow evaluated CVSS 4.1 and ActionableScore 1 with primitive class CLASS_B and manual review REQUIRED. Its independently reconciled impact was MODERATE_KPANIC. Cross model aggregation changed the production result under an enabled evidence gated merge rule. The final reported impact is MODERATE_KPANIC.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 1)	MAYBE	USB INIT PRINTF-TTY UAF LINUS  DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN4 KPANIC V39_AEGIS_ONE_STEP_UP MANUAL_REVIEW_REQUIRED	-	-	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=1
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: 1
* Conservative score: 1
* Raw paranoid score: 1
* Paranoid score: 1
* No floor or cap was applied.
* Final recommended bucket: **Ordinary Moderate**::

2. Signal breakdown

Positive signals:

* +2 Real UAF. The commit directly establishes that completion handlers can access freed USB serial port data after the port drivers are unbound while USB I/O remains active.
* +1 Reliable kernel crash or strong DoS. Asynchronous dereference of released port data can realistically cause an Oops or panic.

Negative signals:

* -2 Host-admin-equivalent privilege. The complete vulnerable sequence is driver registration failure or module unloading, which requires host-level CAP_SYS_MODULE or equivalent control.

Not awarded:

* No race penalty. The patch establishes unsafe deregistration ordering, but does not establish an unusually narrow or uncontrollable timing window.
* No structured stale-object leverage. The port object is structured, but no controlled reclaim, replacement contents, callback consumption, or useful post-free field manipulation is shown.
* No attacker-influenced lifetime bonus. A local process or USB device can influence I/O timing, but cannot perform the required module deregistration without host-admin authority.
* No extra Availability point. It would duplicate the same potential kernel crash.
* No C/I points. The UAF is real, but disclosure, directed write, or protected-state modification is not established.
* No repeated release/refcount signal. The patch does not show two lifetime-mutating operations on the same dangling reference.
* No remote, namespace, authorization-bypass, B3, B4, B5-R, V32, or V33 signal.

3. Reachability analysis

The complete trigger requires unloading or deregistering a USB serial driver, or reaching the registration error unwind. These operations require host-level CAP_SYS_MODULE and are not scoped to an attacker-created user or network namespace.

A connected USB device or local process using the serial port may keep I/O active and affect completion timing, but neither can independently execute the required module teardown. This is therefore a compound influence scenario with host administration controlling object teardown.

Numeric UID 0 is not intrinsically required because CAP_SYS_MODULE is the effective requirement, but that capability is host-admin-equivalent. No network trigger is established. USB serial hardware and active outstanding I/O are practical prerequisites, but no rare-hardware penalty is justified.

4. Primitive and severity interpretation

The exact primitive is asynchronous post-lifetime access to freed USB serial port data by a completion handler. This is a real CLASS_B UAF involving a structured port object, but the demonstrated path is limited to module teardown or registration unwind.

This is closer to a constrained asynchronous teardown UAF than to an active-object replacement primitive. There is no concrete second release, refcount mutation, controlled reclaim, attacker-shaped replacement, arbitrary access, or authorization boundary bypass.

The demonstrated consequence is potential kernel crash or DoS. Confidentiality impact, integrity impact, and privilege escalation remain theoretical and unsupported by the supplied call path.

ImportantCandidate is NO because host-admin authority is required and no useful exploitation leverage beyond stale access is established. AutoDowngradeAllowed is YES because this is a constrained teardown UAF without unresolved repeated-lifetime mutation or a security-boundary primitive.

5. One-sentence report phrase

Incorrect USB serial driver deregistration ordering can leave I/O active after port data is released, allowing a completion handler to access freed memory and potentially crash the kernel during a host-privileged module unload.

6. Manual review recommendation

MANUAL CHECK RECOMMENDED

The UAF is concrete, but the supplied evidence supports a host-admin-gated asynchronous teardown failure without a controlled corruption or privilege-escalation primitive.

7. Call-site confidence

Call-site confidence: medium

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

Patch: USB: serial: fix driver deregistration order
Commit: 9b085a06a0a411b0bcdf18b61c3ebf1be1c72ffe
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=9b085a06a0a411b0bcdf18b61c3ebf1be1c72ffe

Commit description:

USB serial driver modules register one driver for the USB bus and one or
more drivers for the ports on the USB serial bus.

When unloading a driver module, the USB driver must be deregistered
before the USB serial bus drivers so that I/O is stopped before
unbinding the ports to avoid use-after-free in completion handlers
accessing port data.

Note that the "new_id" attributes must first be removed to prevent new
ids from being added and triggering a probe of the USB driver after it
has been deregistered.

Fixes: 765e0ba ("usb-serial: new API for driver registration")
Cc: stable@vger.kernel.org	# 3.4
Cc: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Johan Hovold <johan@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  drivers/usb/serial/bus.c
  drivers/usb/serial/usb-serial.c
  include/linux/usb/serial.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=9b085a06a0a411b0bcdf18b61c3ebf1be1c72ffe

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

The original Linux kernel CVE announcement for CVE-2026-98696 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98696

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:L/I:L/A:H
  The Best / paranoid CVSS vector: AV:L/AC:H/PR:H/UI:N/S:U/C:H/I:H/A:H
  The Best / paranoid CVSS score: 6.4

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: 1

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).