[CVE-2026-53150][MODERATE 7.0] thunderbolt: Reject zero-length property entries in validator

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

CVE: CVE-2026-53150
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: thunderbolt: Reject zero-length property entries in validator
Commit: 581c2053ab4dbe27e83c9e62deb4c73aa8dc0c3a
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=581c2053ab4dbe27e83c9e62deb4c73aa8dc0c3a
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53150
Analysis date: Thu, 25 Jun 2026 20:04:33 -0400
ActionableScore: 7
ActionableScore lower bound: 4
Actionable bucket: Strong Important candidate / Actionable Moderate at minimum
Manual review required: YES

Summary:
A zero-length Thunderbolt XDomain TEXT property can pass validation and cause a one-byte kernel OOB write before the allocation during null termination, allowing a malicious Thunderbolt or USB4 peer to corrupt kernel memory and potentially crash the host.

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ABOUT THIS REPORT
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The original Linux kernel CVE announcement for CVE-2026-53150 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53150

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-2026-53150	MODERATE	CHECK	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:A/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H';*CWE-787;CWE-191;*CWE-20;Other CVSS 'AV:P/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:H';BEST CVSS score: '8.8';DESCR 'A one byte out of bounds write exists in the Thunderbolt XDomain property parser because tb_property_entry_valid accepts zero length TEXT property entries. The later null termination logic writes to property value text at length * 4 - 1, which becomes an offset before the allocation when length is zero. A malicious Thunderbolt or USB4 XDomain peer or device can potentially supply such a malformed property entry and corrupt kernel memory. For the CVSS the PR:N is used because the attacker does not need an account or privileges on the victim once access to the Thunderbolt or XDomain connection is available. The base score treats this as physical access with limited confidentiality and integrity impact plus high availability impact. The paranoid score treats the XDomain peer as adjacent and uses C:H/I:H/A:H because the bug is an OOB write in kernel memory and may require manual review for privilege escalation potential.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 6)  SKIP CVE-2026-53150  SKIP No affected files built, so skip this CVE NO  - - unknown 	MAYBE	OOB SIMPLEFIX IMPROVEONLY KPANIC  KPANIC INCREASED_TO_HIGH_BASED_ON_GUESSCVSS KPANIC DECREASED_TO_MODERATE70_BASED_ON_ACTIONABLESCORELOWERTHAN7	-	-	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=7
ActionableScoreLower=4

## 1. ActionableScore

* Conservative score: 4
* Paranoid score: 7
* Final recommended bucket: **Strong Important candidate / Actionable Moderate at minimum**::

## 2. Signal breakdown

Paranoid scoring signals:

* Firmware-mediated external influence: +1. Malformed XDomain properties can plausibly originate from a Thunderbolt or USB4 peer/device.
* Constrained kernel buffer overwrite: +1. The bug is a one-byte write before the allocation, but the payload is fixed as NUL.
* Weak LPE concern: +1. Kernel heap OOB write creates a plausible corruption sink, but no controlled overwrite or reclaim primitive is demonstrated.
* Reliable kernel crash / strong DoS: +1. A malformed property can corrupt kernel memory and plausibly crash the host.
* Privileged kernel/device-management memory corruption path: +1. The corruption occurs inside a trusted Thunderbolt kernel driver parsing device/peer supplied metadata.
* Confidentiality impact plausible: +1. Paranoid interpretation keeps possible C impact because kernel memory corruption may expose secondary effects.
* Integrity impact plausible: +1. The primitive is a kernel memory write before an allocated object.
* Availability impact realistic: +1. Repeated malformed external input can plausibly cause host-wide crashes.
* Corruption primitive highly constrained: -1. The write is only one byte and the value is fixed.
* Physical/rare hardware condition: -1 in paranoid scoring. Triggering requires Thunderbolt/USB4/XDomain exposure, but this is still an external hardware attack surface.

Conservative lower score uses the same bug class but applies a stronger physical-only penalty and does not assume confidentiality impact, giving ActionableScoreLower=4.

## 3. Reachability analysis

The realistic attacker is a malicious Thunderbolt/USB4/XDomain peer or device, or a compromised peer participating in the XDomain property protocol. No local account on the victim is required once the attacker can influence that Thunderbolt/XDomain connection. This is not Internet remote and should not be scored like a normal network service. Namespaces and containers are not the main access-control boundary here because the trigger is device/protocol supplied metadata handled by the host kernel driver. Exposure depends on Thunderbolt/USB4 hardware, kernel Thunderbolt support, and whether XDomain property exchange is reachable in the deployment.

## 4. Severity interpretation

This is not a simple warning or DoS-only logic bug. The patch directly fixes an integer underflow leading to a one-byte OOB write in kernel memory. Realistic exploitation beyond crash is uncertain because the overwrite value is fixed and the target is not shown to be attacker-selected. However, because it is an externally influenced kernel memory corruption in a device-management path, it should not be auto-closed as an ordinary Moderate issue.

## 5. One-sentence report phrase

A zero-length Thunderbolt XDomain TEXT property can pass validation and cause a one-byte kernel OOB write before the allocation during null termination, allowing a malicious Thunderbolt or USB4 peer to corrupt kernel memory and potentially crash the host.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

Reason: this is externally influenced kernel memory corruption, even though the primitive is constrained to a fixed one-byte underwrite. Manual review should verify reachability of the XDomain property path, allocation layout, and whether the underwrite can corrupt adjacent kernel objects in a security-relevant way.

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

Patch: thunderbolt: Reject zero-length property entries in validator
Commit: 581c2053ab4dbe27e83c9e62deb4c73aa8dc0c3a
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=581c2053ab4dbe27e83c9e62deb4c73aa8dc0c3a

Commit description:

tb_property_entry_valid() accepts entries with length == 0 for
DIRECTORY, DATA, and TEXT types.  A zero-length TEXT entry passes
validation but causes an underflow in the null-termination logic:

  property->value.text[property->length * 4 - 1] = '\0';

When property->length is 0 this writes to offset -1 relative to
the allocation.

Reject zero-length entries early in the validator since they have no
valid representation in the XDomain property protocol.

Fixes: cdae7c0 ("thunderbolt: Add support for XDomain properties")
Cc: stable@vger.kernel.org
Assisted-by: Claude:claude-opus-4-7
Signed-off-by: Michael Bommarito <michael.bommarito@gmail.com>
Signed-off-by: Mika Westerberg <mika.westerberg@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  drivers/thunderbolt/property.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=581c2053ab4dbe27e83c9e62deb4c73aa8dc0c3a

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

The original Linux kernel CVE announcement for CVE-2026-53150 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53150

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:L/I:L/A:H
  The Best / paranoid CVSS vector: AV:A/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
  The Best / paranoid CVSS score: 8.8

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: 4
  Paranoid ActionableScore: 7

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).