[CVE-2026-98772][MODERATE 7.0] USB: serial: fix port tear down use-after-free

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

CVE: CVE-2026-98772
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: USB: serial: fix port tear down use-after-free
Commit: 60cc9379c3e650d1ebfba4de63f1242537a62a32
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=60cc9379c3e650d1ebfba4de63f1242537a62a32
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98772
Analysis date: Sat, 24 Oct 2026 07:14:52 -0400
ActionableScore: 1
ActionableScore lower bound: unknown
Actionable bucket: Ordinary Moderate
Manual review required: NO

Summary:
A physical USB serial device can race disconnect teardown with a shared-URB completion handler, causing a constrained use-after-free and possible kernel crash.

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

The original Linux kernel CVE announcement for CVE-2026-98772 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98772

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
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CVE-2026-98772	MODERATE	https://www.kernelcve.org/list/?q=CVE-2026-98772 CHECK WITH IMPACT FROM ORIG NN MODERATE | AEGIS IMPACT MODERATE_KPANIC AEGIS_AS=5 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:P/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:N/I:N/A:H';BEST CVSS score: '6.4';DESCR 'A race in USB serial disconnect handling can deregister a port and free its driver data while a completion handler for a shared URB is still running or can still run. The demonstrated primitive is a use after free access from asynchronous kernel I O, with a kernel crash as the primary supported impact. No specific information leak or controlled write is shown, so the base CIA is N,N,H. The paranoid H,H,H vector reflects the still defensible possibility that a driver completion callback writes through stale state after the freed memory has been reused. For the CVSS the PR:N value is used because a malicious USB device can trigger attach, I O, and physical disconnect without an authenticated host account. Exploitation still requires physical USB access and successful race timing. 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 2.0 and ActionableScore 5 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	LOCK USB INIT PRINTF-TTY RACE UAF HARDWARE LINUS SYZBOT  DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN4 KPANIC V39_AEGIS_ONE_STEP_UP MANUAL_REVIEW_REQUIRED	-	-	checked

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

ActionableScore=1
PrimitiveClass=CLASS_B
RealUAF=YES
HostAdminRequired=NO
NamespaceScopedPrivilege=NO
ImportantCandidate=NO
ManualReview=RECOMMENDED
AutoDowngradeAllowed=YES
RequiresHostUID0=NO
AuthorizationDecisionBypass=NO
ProtectedResourceImpact=NONE
B4PendingReview=NO
B4PendingConfirmed=NO

1. ActionableScore

* Raw base score: 1 (+2 UAF, +1 plausible kernel crash, +1 device-mediated influence, -2 physical access, -1 difficult race timing).
* Conservative score: 1. No UAF floor applies because this is constrained asynchronous access to fixed driver state.
* Raw paranoid score: 1.
* Paranoid score: 1. Theoretical writes through reclaimed state are not scored without a shown stale write or controlled reuse.
* Final recommended bucket: **Ordinary Moderate**::

2. Signal breakdown

* +2: Real UAF. Port driver data can be freed by `device_del()` while a shared-URB completion handler still accesses it.
* +1: A stale completion-handler access plausibly causes an Oops or kernel crash.
* +1: A malicious USB device can influence asynchronous I/O and disconnect behavior through the device-mediated path.
* -2: The supplied attack model requires physical USB-device access.
* -1: The supplied evidence identifies successful asynchronous teardown/completion race timing as necessary.
* No controlled reclaim, stale write, attacker-shaped replacement, repeated release, arbitrary write, disclosure, or protected-state modification is shown.
* No extra availability point: it would duplicate the same crash.
* NEW52/B5-R and NEW53/B3-PENDING do not apply: no accumulated OOB write or shared-backing write exists.

3. Reachability analysis

A malicious physical USB device can initiate device activity and disconnect without host credentials, so host-admin and host UID 0 are not required. No namespace capability is involved. Physical attachment and successful completion-versus-teardown timing are prerequisites; no special rare hardware beyond a suitable USB serial device is established.

4. Primitive and severity reading

The primitive is an asynchronous UAF of fixed port driver state: deregistration can free that state before shared URBs are fully stopped. The fix postpones port deregistration until hangup and the driver disconnect callback have stopped I/O. The supported effect is stale access and possible host crash. No specific post-free write or useful field consumption is shown, so this remains constrained CLASS_B rather than CLASS_A. ImportantCandidate is NO and auto-downgrade is allowed because exploit leverage beyond crash is unsupported.

There is no authorization decision or protected-resource access, so B4 pending review is inapplicable.

5. One-sentence report phrase

A physical USB serial device can race disconnect teardown with a shared-URB completion handler, causing a constrained use-after-free and possible kernel crash.

6. Manual review advice

MANUAL CHECK RECOMMENDED

Confirm affected drivers and whether any completion callback writes through freed driver state before final severity assignment.

7. Call-site confidence

Call-site confidence: medium

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

Patch: USB: serial: fix port tear down use-after-free
Commit: 60cc9379c3e650d1ebfba4de63f1242537a62a32
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=60cc9379c3e650d1ebfba4de63f1242537a62a32

Commit description:

Some drivers for multiport devices access port driver data from
completion handlers of shared URBs submitted at attach() or first open()
and stopped at disconnect() or last close(), respectively.

A simple NULL check before accessing the driver data makes sure that a
port state container has at least been allocated, but a completion
handler can still race with port tear down.

Reorder the disconnect handling so that ports are not deregistered (and
their driver data freed) until after all ports have been hung up and the
driver disconnect() callback has run so that all I/O has been stopped.

Fixes: 2d93148 ("USB: serial: fix lifetime and locking problems")
Reported-by: syzbot+e5e28c3e953b2eebb16e@syzkaller.appspotmail.com
Link: https://lore.kernel.org/all/6a7e6fb9.ec5dc6cc.21cb3f.00c0.GAE@google.com/
Cc: stable@vger.kernel.org	# 2.6.30
Cc: Alan Stern <stern@rowland.harvard.edu>
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Johan Hovold <johan@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  drivers/usb/serial/usb-serial.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=60cc9379c3e650d1ebfba4de63f1242537a62a32

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

The original Linux kernel CVE announcement for CVE-2026-98772 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98772

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:N/I:N/A:H
  The Best / paranoid CVSS vector: AV:P/AC:H/PR:N/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).