[CVE-2026-98695][MODERATE REGULAR] USB: serial: fix ioctl hangup race

[CVE-2026-98695][MODERATE REGULAR] USB: serial: fix ioctl hangup race

[AL-KERNEL]

CVE: CVE-2026-98695
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: USB: serial: fix ioctl hangup race
Commit: ae0da9a5c1ca95c20cc5feffd511ce6eae75924e
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=ae0da9a5c1ca95c20cc5feffd511ce6eae75924e
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98695
Analysis date: Sun, 18 Oct 2026 22:23:03 -0400
ActionableScore: 1
ActionableScore lower bound: unknown
Actionable bucket: Ordinary Moderate
Manual review required: NO

Summary:
A race between USB serial tty operations and concurrent hangup or disconnection can invoke a driver callback after the port becomes invalid, causing a kernel NULL pointer dereference and possible denial of service.

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

The original Linux kernel CVE announcement for CVE-2026-98695 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98695

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.

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

CVE-2026-98695	MODERATE	https://www.kernelcve.org/list/?q=CVE-2026-98695 CHECK WITH IMPACT FROM ORIG NN LOW | AEGIS IMPACT MODERATE_KPANIC AEGIS_AS=1 LEGACY=MODERATE RESULT=DIFF V39_AEGIS_ONE_STEP_UP=LOW->MODERATE TEMP_DISTANCE_MERGE_SKIP=AEGIS_NO_POSITIVE_SEVERITY_EVIDENCE (final 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:L/UI:N/S:U/C:N/I:N/A:H';CWE-362;**CWE-476;CWE-667;*CWE-672;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '4.7';DESCR 'A race between USB serial tty operations and hangup can invoke a driver callback after the device has been disconnected or powered down. A local process can issue an affected ioctl or a lengthy break operation while a concurrent disconnect changes the port state, which can cause a NULL pointer dereference in the kernel. For the CVSS the PR:L reflects that the attacker needs local access to the relevant tty device but does not necessarily need full administrative privileges to invoke the affected tty operations. AC:H is used because successful triggering depends on winning a timing window between the operation and hangup or device removal. The issue is not network reachable. Impact is at least disruption of the affected tty operation and may become a host denial of service through a kernel Oops, lockup, or panic depending on kernel configuration. The supplied code supports a NULL pointer dereference but does not establish a UAF, OOB write, information leak, or arbitrary write primitive. Automated impact decision path. The original SimpleNet classifier selected LOW. The primary LLM estimated paranoid CVSS 4.7 and the production ActionableScore returned 1 with recommendation Ordinary Moderate. The production rules then evaluated CVSS thresholds and ActionableScore thresholds. Recorded rule transitions were final reconciliation stage LOW to MODERATE 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 V39_AEGIS_ONE_STEP_UP and MANUAL_REVIEW_REQUIRED. The independent weaker Aegis shadow evaluated CVSS 2.5 and ActionableScore 1 with primitive class CLASS_C and manual review RECOMMENDED. 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.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 1)	MAYBE	LOCK USB INIT PRINTF-TTY RACE HARDWARE LINUS SYZBOT V39_AEGIS_ONE_STEP_UP MANUAL_REVIEW_REQUIRED	-	-	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=1
PrimitiveClass=CLASS_C
RealUAF=NO
HostAdminRequired=UNKNOWN
NamespaceScopedPrivilege=NO
ImportantCandidate=NO
ManualReview=RECOMMENDED
AutoDowngradeAllowed=YES
RequiresHostUID0=UNKNOWN
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 applied.
* Final recommended bucket: **Ordinary Moderate**::

2. Signal breakdown

* +1 Reliable kernel crash or strong DoS concern. The commit directly establishes a kernel NULL pointer dereference when disconnect races with lengthy break signalling. Depending on kernel configuration, this can produce an Oops, lockup, or panic.
* +0 Weak corruption concern. Calling a driver callback after disconnect establishes invalid-state use and a NULL dereference, but not a useful memory-corruption primitive.
* No local-unprivileged bonus. Access to an affected tty may be delegated, but control over the complete ioctl plus disconnect sequence is not established for an ordinary user.
* No host-admin penalty. Host-admin-equivalent privilege is also not positively established.
* No race penalty. The lengthy break operation may provide a controllable window, so the race is not shown to be narrow or difficult enough for minus one.
* No UAF signal. The evidence does not show that `usb_serial_port`, driver-private data, or another object is freed before use.
* No controlled reclaim, OOB write, arbitrary write, disclosure, authorization bypass, or privilege-escalation primitive is demonstrated.
* No additional Availability point. The same NULL-dereference failure is not counted twice.
* NEW52 B5-R does not apply because no retry-accumulated heap OOB write exists.
* NEW53 B3-PENDING does not apply because no shared-backing write exists.
* V33 and V32 do not apply because no attacker-influenced active structured corruption or checksum-metadata write exists.
* B4-PENDING does not apply because `tty_io_error()` is a device-state check, not an authorization guard changing a security decision from DENY to ALLOW.

3. Reachability analysis

A process must have access to the affected USB serial tty and invoke an affected operation, such as lengthy break signalling, while hangup or device disconnection occurs concurrently. Device-node permissions may allow a non-root user to issue the tty operation, but the supplied evidence does not establish whether the same attacker can initiate software removal, power-down, or physical disconnection.

The complete trigger may therefore involve a user with tty access plus physical device removal, or a more privileged USB-management actor. No user-namespace or network-namespace capability path is involved. A compatible USB serial device and loaded driver are prerequisites. No network trigger, sysctl, or unusual boot option is identified. The race appears repeatable when disconnect can be coordinated with lengthy signalling, but complete below-host-admin reachability remains unresolved.

4. Primitive and severity interpretation

The exact primitive is a race-driven callback into a USB serial driver after the tty port has been hung up or the device has been disconnected or powered down. The demonstrated terminal behavior is a NULL pointer dereference. This is invalid active-state consumption, but it is not an established post-lifetime object use.

There is no concrete repeated release or refcount operation. No first operation is shown to free an object while the same reference survives into a second lifetime mutation. The case is therefore CLASS_C rather than CLASS_B.

The demonstrated consequence is kernel Oops or denial of service. A host panic is plausible under configurations such as `panic_on_oops`, but no independent confidentiality, integrity, UAF, or privilege-escalation mechanism is supported. ImportantCandidate is NO because no useful corruption or security-boundary primitive remains after excluding the crash. AutoDowngradeAllowed is YES because this is a constrained race and NULL-dereference case without unresolved exploitation leverage.

5. One-sentence report phrase

A race between USB serial tty operations and concurrent hangup or disconnection can invoke a driver callback after the port becomes invalid, causing a kernel NULL pointer dereference and possible denial of service.

6. Manual review recommendation

MANUAL CHECK RECOMMENDED

Confirm device-node permissions, who can initiate disconnect, and whether any driver-specific callback accesses freed private state rather than only producing the documented NULL dereference.

7. Call-site confidence

Call-site confidence: high

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

Patch: USB: serial: fix ioctl hangup race
Commit: ae0da9a5c1ca95c20cc5feffd511ce6eae75924e
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=ae0da9a5c1ca95c20cc5feffd511ce6eae75924e

Commit description:

The tty ioctls can race with hangup and end up calling into a tty driver
for a device that is already gone or powered down.

Serialise the callbacks using the tty port mutex and add the missing
checks to make sure the port has not been hung up before accessing port
driver data or hardware.

This specifically avoids dereferencing a NULL-pointer if a device is
disconnected during lengthy break signalling.

Note that TIOCGICOUNT and TIOCMIWAIT do not access port driver data or
hardware and are therefore not affected by the race.

Fixes: f34d7a5 ("tty: The big operations rework")
Reported-by: Nick Bowler <nbowler@draconx.ca>
Link: https://lore.kernel.org/all/CADyTPExB2kYOOwkO0JqGhKaYVDqO9uS9WCw0J=MCTdVhcGOogA@mail.gmail.com/
Reported-by: syzbot+473d7477c523b41d4046@syzkaller.appspotmail.com
Closes: https://lore.kernel.org/r/6a9087a4.4d659fcc.734b4.0013.GAE@google.com
Cc: stable@vger.kernel.org	# 2.6.26
Signed-off-by: Johan Hovold <johan@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  drivers/usb/serial/generic.c
  drivers/usb/serial/usb-serial.c
  drivers/usb/serial/xr_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=ae0da9a5c1ca95c20cc5feffd511ce6eae75924e

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

The original Linux kernel CVE announcement for CVE-2026-98695 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98695

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:L/UI:N/S:U/C:N/I:N/A:L
  The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS score: 4.7

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: 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).