[CVE-2026-74575][MODERATE 7.0] thunderbolt: Prevent XDomain delayed work use-after-free on disconnect [ Upstream

[CVE-2026-74575][MODERATE 7.0] thunderbolt: Prevent XDomain delayed work use-after-free on disconnect [ Upstream

[AL-KERNEL]

CVE: CVE-2026-74575
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: thunderbolt: Prevent XDomain delayed work use-after-free on disconnect [ Upstream
Commit: 91b40862a02000f490b63f1d315be3ee31e83871
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=91b40862a02000f490b63f1d315be3ee31e83871
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74575
Analysis date: Sat, 15 Aug 2026 11:40:46 -0400
ActionableScore: 5
ActionableScore lower bound: 4
Actionable bucket: Strong Important candidate / Actionable Moderate at minimum
Manual review required: YES

Summary:
A Thunderbolt XDomain disconnect race can allow delayed work to be queued after cancellation and later run on a freed xdomain object, causing a kernel use-after-free reachable from an attached Thunderbolt/USB4 peer and requiring manual review for impact beyond DoS.

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ABOUT THIS REPORT
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The original Linux kernel CVE announcement for CVE-2026-74575 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74575

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-2026-74575	MODERATE	CHECK WITH IMPACT FROM ORIG NN MODERATE	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:A/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H';*CWE-416;CWE-362;CWE-667;Other CVSS 'AV:P/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '7.5';DESCR 'Thunderbolt XDomain delayed work can be queued after tb_xdomain_remove has already canceled pending work but before device_unregister frees the xdomain object. A remote peer on the Thunderbolt/USB4 link can send XDomain requests such as PROPERTIES_CHANGED_REQUEST, UUID_REQUEST, or LINK_STATE_CHANGE_REQUEST while disconnect handling is running, creating a race where state_work or properties_changed_work later runs on freed memory. For the CVSS the PR:N is used because the attacker does not need a local account or privileges on the victim host, but does need access to a connected Thunderbolt/USB4 peer or device path. The issue is not Internet network reachable and is best treated as physical or adjacent bus reachable. Impact is at least denial of service via kernel crash. Because this is a real use after free in kernel delayed work, worst case confidentiality and integrity impact are plausible and should be reviewed manually.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 5)  SKIP CVE-2026-74575 UNKNOWN SKIP No affected files built, so skip this CVE NO  - - unknown 	MAYBE	LOCK DANGER INIT UAF HARDWARE DEBUGFS KPANIC  KPANIC INCREASED_TO_HIGH_BASED_ON_GUESSCVSS KPANIC DECREASED_TO_MODERATE70_BASED_ON_ACTIONABLESCORELOWERTHAN6	-	-	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=5
ActionableScoreLower=4

## 1. ActionableScore

* Conservative score: 4
* Paranoid score: 5
* Final recommended bucket: **Strong Important candidate / Actionable Moderate at minimum**::

## 2. Signal breakdown

* Firmware-mediated or external device influence: +1
  The trigger can come from a Thunderbolt/USB4 XDomain peer sending XDomain requests while disconnect handling is running. This is not Internet remote, but it is externally influenced through an attached bus peer.

* Memory corruption, weak/indirect corruption candidate: +1
  The bug is a race-dependent UAF where delayed work can run after the xdomain object is freed. No attacker-controlled reclaim, overwrite target, or arbitrary write primitive is shown.

* Real lifetime corruption: +1
  The patch fixes a real lifetime mismatch between queue_delayed_work(), cancel_delayed_work_sync(), device_unregister(), and eventual object free.

* Reliable kernel crash / strong DoS: +1
  Delayed work executing on a freed kernel object is a credible kernel crash path.

* Availability impact realistic: +1
  The likely practical impact is host kernel crash or serious instability during disconnect handling.

* Hard or unreliable race / special timing required: -1
  The issue requires a narrow race between request handling and XDomain removal.

* Paranoid weak LPE concern: +1
  For the paranoid score only, this is a kernel UAF involving asynchronous work execution on a freed object. There is no demonstrated exploit primitive, but the class is significant enough for manual review.

I do not apply the full physical-only penalty as a dominant downgrade because Thunderbolt/USB4 XDomain is an intended external connectivity path on affected systems, not merely an obscure debug mode. The exposure is adjacent/physical-bus rather than AV:N.

## 3. Reachability analysis

The bug can be triggered by a connected Thunderbolt/USB4 peer that can send XDomain protocol requests during disconnect or removal. A local unprivileged account on the victim is not required, so this is closer to PR:N in CVSS terms, but realistic exploitation requires physical or adjacent-bus access to the host. Namespaces and containers do not materially affect reachability because the trigger is not a normal local userspace syscall path. The path is only relevant on systems with Thunderbolt/USB4 and XDomain functionality active, so it is not broadly Internet-exposed.

## 4. Severity interpretation

This is more than an ordinary Moderate correctness issue because it is a real kernel UAF in delayed work lifetime handling. Realistically, the most supported impact is DoS through a kernel crash. Theoretical confidentiality or integrity impact is not proven because the patch does not show attacker-controlled reclaim, type confusion, arbitrary write, or controlled callback replacement. Paranoid triage should still keep it as Actionable Moderate at minimum because kernel lifetime bugs in asynchronous work paths are historically under-triaged.

## 5. One-sentence report phrase

A Thunderbolt XDomain disconnect race can allow delayed work to be queued after cancellation and later run on a freed xdomain object, causing a kernel use-after-free reachable from an attached Thunderbolt/USB4 peer and requiring manual review for impact beyond DoS.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

Reason: this is a race-based kernel UAF in an asynchronous workqueue path with external bus influence. No strong LPE primitive is demonstrated, but the lifetime-corruption class and adjacent-device trigger make auto-closure inappropriate.

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

Patch: thunderbolt: Prevent XDomain delayed work use-after-free on disconnect [ Upstream
Commit: 91b40862a02000f490b63f1d315be3ee31e83871
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=91b40862a02000f490b63f1d315be3ee31e83871

Changed files:
  drivers/thunderbolt/xdomain.c
  include/linux/thunderbolt.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=91b40862a02000f490b63f1d315be3ee31e83871

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

The original Linux kernel CVE announcement for CVE-2026-74575 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74575

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:A/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H
  The Best / paranoid CVSS score: 7.5

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: 4
  Paranoid ActionableScore: 5

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).