[CVE-2026-98693][MODERATE 7.0] thunderbolt: Hold a router reference for each allocated HopID

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

CVE: CVE-2026-98693
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: thunderbolt: Hold a router reference for each allocated HopID
Commit: c444d2c17dc236680324fd989232199680a6c419
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=c444d2c17dc236680324fd989232199680a6c419
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98693
Analysis date: Sat, 24 Oct 2026 06:20:18 -0400
ActionableScore: 2
ActionableScore lower bound: unknown
Actionable bucket: Ordinary Moderate
Manual review required: NO

Summary:
Physical Thunderbolt cable removal can race outstanding DisplayPort work with router teardown, causing `ida_free()` to consume HopID allocator state embedded in an already freed router.

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ABOUT THIS REPORT
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The original Linux kernel CVE announcement for CVE-2026-98693 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98693

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-2026-98693	MODERATE	https://www.kernelcve.org/list/?q=CVE-2026-98693 CHECK WITH IMPACT FROM ORIG NN MODERATE | AEGIS IMPACT MODERATE_KPANIC AEGIS_AS=4 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:L/PR:N/UI:N/S:U/C:H/I:H/A:H';*CWE-416;CWE-362;*CWE-664;Other CVSS 'AV:P/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '6.8';DESCR 'An asynchronous DisplayPort tunnel can outlive tb_switch_remove because tb_stop drops tunnel references lacking deactivating the tunnel or cancelling an in flight dprx_work. Later tb_path_free can release HopIDs through IDAs embedded in an already freed router and its ports, creating a use after free access with observed ida_free warnings and a plausible memory corruption risk. The Apple NHI path is reliably triggered by physically unplugging the cable while the DPRX capability read is still pending, while software driver unbind normally requires administrative control. For the CVSS the PR:N value is used for the paranoid physical attack path because cable removal requires physical access but no logical privileges on the target. Base impact is host denial of service, while the paranoid score includes confidentiality and integrity impact because ida_free operates on freed allocator state, although controlled exploitation is not established. Automated impact decision path. The original SimpleNet classifier selected MODERATE. The primary LLM estimated paranoid CVSS 6.8 and the production ActionableScore returned 2 with recommendation Ordinary Moderate. The production rules then evaluated CVSS thresholds and ActionableScore thresholds. Recorded rule transitions were CVSS and initial triage stage MODERATE to MODERATE_KPANIC because the CVSS score, vector or bug class threshold rule was applied. 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 INCREASED_TO_MODERATE7_BASED_ON_GUESSCVSS and DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN4 and V39_AEGIS_ONE_STEP_UP and MANUAL_REVIEW_REQUIRED. The independent weaker Aegis shadow evaluated CVSS 2.4 and ActionableScore 4 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 2)	MAYBE	INIT UAF HARDWARE LINUS TEST  INCREASED_TO_MODERATE7_BASED_ON_GUESSCVSS 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=2
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: 2 (+2 UAF, +1 plausible kernel crash, +1 hardware-mediated external trigger, -2 physical-access requirement).
* Conservative score: 2. No floor applied because physical access is a specific strong reducing condition.
* Raw paranoid score: 2. Theoretical allocator corruption, disclosure, or code execution is not scored.
* Paranoid score: 2.
* Final recommended bucket: **Ordinary Moderate**::

2. Signal breakdown

* +2 Real UAF/lifetime violation: `dprx_work` can retain a tunnel after `tb_switch_remove()` frees the router and its embedded port HopID IDAs; later `tb_path_free()` reaches those stale IDAs.
* +1 Reliable crash/strong-DoS concern: `ida_free()` operates on expired state and produces allocator warnings; a kernel fault is plausible, though panic is not demonstrated.
* +1 Firmware/hardware-mediated influence: cable removal on Apple NHI reliably initiates teardown while the DPRX capability read remains pending.
* -2 Physical-access requirement: the demonstrated below-host-admin path requires physically unplugging the cable. Software driver unbind instead requires administrative control.
* No hard-race penalty: the Apple NHI ordering is described as reliable.
* No structured-leverage or strong-corruption bonus: attacker-controlled reclaim, stale contents, target selection, callback consumption, and a confirmed post-free write are not shown.
* No C/I points: the legacy C:H/I:H interpretation is speculative.
* NEW52 B5-R does not apply: no retry-accumulated heap OOB write exists.
* NEW53/B3 and NEW54/B4 do not apply: no shared-backing write or authorization decision is involved.

3. Reachability analysis

A person with physical access can unplug the Thunderbolt cable while a DisplayPort tunnel waits for DPRX capability completion. This needs neither host UID 0 nor a namespace capability, so `HostAdminRequired=NO`; however, it is a physical rather than ordinary local-software trigger. The alternative unbind route is host-administrative. No namespace, prior delegation, or remotely reachable path is shown. Special Apple NHI behavior makes the reliable path hardware-specific.

4. Primitive and severity reading

The primitive is a real active-object lifetime violation: asynchronous tunnel work outlives router removal, followed by `ida_free()` through IDAs embedded in the freed router/ports. This is CLASS_B, not merely a passive warning, but the evidence shows neither controlled replacement nor a confirmed useful post-free write. The supported impact is warning/crash/host DoS; stronger memory corruption is unresolved. Therefore it is not presently an Important candidate and may be downgraded after review.

5. One-sentence report phrase

Physical Thunderbolt cable removal can race outstanding DisplayPort work with router teardown, causing `ida_free()` to consume HopID allocator state embedded in an already freed router.

6. Manual review advice

MANUAL CHECK RECOMMENDED

Confirm whether `ida_free()` can mutate reclaimed slab state before its warning path and whether non-physical, below-host-admin triggering exists.

7. Call-site confidence

Call-site confidence: high

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

Patch: thunderbolt: Hold a router reference for each allocated HopID
Commit: c444d2c17dc236680324fd989232199680a6c419
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=c444d2c17dc236680324fd989232199680a6c419

Commit description:

tb_stop() drops the reference to all DP tunnels but does not deactivate
them, thus nothing cancels a dprx_work still in flight (which holds its
own tunnel reference) and the tunnel can outlive tb_switch_remove(). The
HopID releases in tb_path_free() then operate on freed IDAs and trigger
warnings like

  ida_free called for id=8 which is not allocated.

This can be triggered by unbinding the driver while a DP tunnel is still
waiting for the DPRX capabilities read to finish. On the Apple NHI
unplugging the cable runs into just that reliably because the read can
never finish right now and because the unplug powers down the entire
USB4 complex and removes the NHI device.

Take a router reference whenever an input or output HopID is allocated
and drop it again after the HopID is released. This keeps the ports and
their HopID IDAs alive for as long as they are used.

The KUnit tests allocate routers without ever registering their devices
so initialize the embedded struct device there as well and drop its
initial reference when the test is finished.

Fixes: d6d458d ("thunderbolt: Handle DisplayPort tunnel activation asynchronously")
Cc: stable@vger.kernel.org
Signed-off-by: Sven Peter <sven@kernel.org>
Signed-off-by: Mika Westerberg <mika.westerberg@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  drivers/thunderbolt/switch.c
  drivers/thunderbolt/test.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=c444d2c17dc236680324fd989232199680a6c419

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

The original Linux kernel CVE announcement for CVE-2026-98693 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98693

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:L/PR:N/UI:N/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS vector: AV:P/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
  The Best / paranoid CVSS score: 6.8

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: 2

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).