[CVE-2026-98752][MODERATE 7.0] tty: port: fix tty_port_tty_vhangup() race [ Upstream

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

CVE: CVE-2026-98752
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: tty: port: fix tty_port_tty_vhangup() race [ Upstream
Commit: 6d1a984afc3ca477dab3e51ec806671d443ad524
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=6d1a984afc3ca477dab3e51ec806671d443ad524
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98752
Analysis date: Sat, 24 Oct 2026 04:08:00 -0400
ActionableScore: 4
ActionableScore lower bound: unknown
Actionable bucket: Borderline / manual review recommended
Manual review required: YES

Summary:
A hangup serialization race can let tty driver teardown free active resources while racing ioctls or carrier-loss handling still access them, causing a kernel UAF or NULL dereference.

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

The original Linux kernel CVE announcement for CVE-2026-98752 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98752

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-2026-98752	MODERATE	https://www.kernelcve.org/list/?q=CVE-2026-98752 CHECK WITH IMPACT FROM ORIG NN MODERATE | AEGIS IMPACT MODERATE_KPANIC AEGIS_AS=4 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:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H';CWE-362;*CWE-416;**CWE-476;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:H';BEST CVSS score: '7';DESCR 'A race in tty_port_tty_vhangup could let a synchronous hangup return while another hangup was still clearing and shutting down the port. A driver could then deregister the port and free device resources while racing ioctls or asynchronous carrier loss handling still access them, resulting in a use after free or NULL pointer dereference. For the CVSS the PR:L value is selected because reliable triggering normally requires a local user or process with access to the affected tty device, although device permissions and the ability to cause physical disconnect or deregistration vary by driver. AC:H reflects the need to win a hangup and teardown race. Impact is at least a local denial of service via kernel crash and may include confidentiality or integrity impact when a driver specific use after free is exploitable. Automated impact decision path. The original SimpleNet classifier selected MODERATE_KPANIC. The primary LLM estimated paranoid CVSS 7 and the production ActionableScore returned 4 with recommendation Borderline / manual review recommended. The production rules then evaluated CVSS thresholds and ActionableScore thresholds. No severity changing production threshold or specialist override was recorded. 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 has no review artifact for this run. The independent weaker Aegis shadow evaluated CVSS 2.5 and ActionableScore 4 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 Borderline / manual review recommended (with actual score 4)	MAYBE	LOCK INIT PRINTF-TTY RACE UAF HARDWARE LINUS SYZBOT KPANIC 	-	-	checked

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

ActionableScore=4
PrimitiveClass=CLASS_B
RealUAF=YES
HostAdminRequired=UNKNOWN
NamespaceScopedPrivilege=UNKNOWN
ImportantCandidate=NO
ManualReview=RECOMMENDED
AutoDowngradeAllowed=YES
RequiresHostUID0=UNKNOWN
AuthorizationDecisionBypass=NO
ProtectedResourceImpact=NONE
B4PendingReview=NO
B4PendingConfirmed=NO

1. ActionableScore

* Raw base score: 3.
* Conservative score: 4. REAL UAF FLOOR 4 applies because racing operations can access freed active driver resources and host-admin-only reachability is not established.
* Raw paranoid score: 3.
* Paranoid score: 4. No additional technically supported exploit primitive exists.
* Final recommended bucket: **Borderline / manual review recommended**::

2. Signal breakdown

* +2 — Real lifetime violation: premature return from `tty_port_tty_vhangup()` permits driver deregistration and resource teardown while racing ioctls or asynchronous hangups still access those resources.
* +1 — Plausible kernel crash/DoS from the stated UAF and NULL-pointer dereferences.
* +0 — No race penalty: the ordering race is established, but the evidence does not show that it is necessarily narrow, one-shot, or difficult to repeat.
* Floor 4 — The stale accesses involve active driver/port processing rather than clearly fixed stale storage with guaranteed immediate failure.
* No controlled reclaim, attacker-shaped replacement, directed write, callback influence, repeated release/refcount mutation, disclosure, or authorization bypass is shown.
* No extra availability point is awarded for the same crash. The speculative CVSS confidentiality and integrity impacts are not scored.

Repeated-release check: no first-release/surviving-reference/second-release sequence is shown; the dedicated +1, paranoid refcount bonus, and FLOOR 5 do not apply.

3. Reachability analysis

A process with access to the affected tty can race ioctls or hangup activity, but the complete sequence also requires driver deregistration or equivalent teardown, potentially associated with physical disconnect. The evidence does not establish whether an ordinary user can induce that stage, whether host administration is required, or whether any namespace capability suffices. No physical-only or rare-hardware penalty is applied because affected driver constraints are unspecified. Race repeatability is likewise unresolved.

4. Primitive and severity reading

The primitive is a real Class B UAF involving active driver resources, plus possible NULL dereference. The patch serializes synchronous hangup against port shutdown so deregistration cannot proceed before shutdown completes. This is broader than a fixed stale buffer, but the supplied code does not identify the freed object, stale fields consumed, useful post-free mutation, or attacker-controlled reuse.

The shown effect is crash-capable stale access. LPE or confidentiality/integrity compromise remains theoretical. Consequently this is not a strong Important candidate, and auto-downgrade remains permissible after driver-specific review.

5. One-sentence report phrase

A hangup serialization race can let tty driver teardown free active resources while racing ioctls or carrier-loss handling still access them, causing a kernel UAF or NULL dereference.

6. Manual review advice

MANUAL CHECK RECOMMENDED

Review affected driver teardown and ioctl paths for attacker-triggerable deregistration and material post-free field use.

7. Call-site confidence

Call-site confidence: medium

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

Patch: tty: port: fix tty_port_tty_vhangup() race [ Upstream
Commit: 6d1a984afc3ca477dab3e51ec806671d443ad524
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=6d1a984afc3ca477dab3e51ec806671d443ad524

Changed files:
  drivers/tty/tty_port.c
  include/linux/tty_port.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=6d1a984afc3ca477dab3e51ec806671d443ad524

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

The original Linux kernel CVE announcement for CVE-2026-98752 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98752

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:L/I:L/A:H
  The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H
  The Best / paranoid CVSS score: 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: 4

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).