[CVE-2026-53149][MODERATE REGULAR] thunderbolt: Bound root directory content to block size

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

CVE: CVE-2026-53149
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: thunderbolt: Bound root directory content to block size
Commit: 5c7657d38d07268124782f03519f07c22a5814fb
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=5c7657d38d07268124782f03519f07c22a5814fb
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53149
Analysis date: Fri, 26 Jun 2026 05:22:24 -0400
ActionableScore: 3
ActionableScore lower bound: 2
Actionable bucket: Actionable Moderate at minimum
Manual review required: YES

Summary:
A missing root directory bounds check in Thunderbolt XDomain property parsing allows malformed peer or device supplied property data to trigger an out of bounds read past the allocated property block, with realistic impact of kernel crash and possible limited confidentiality concern.

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ABOUT THIS REPORT
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The original Linux kernel CVE announcement for CVE-2026-53149 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53149

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: 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-2026-53149	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:L/I:N/A:H';CWE-125;*CWE-20;CWE-130;Other CVSS 'AV:P/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '7.1';DESCR 'A root directory bounds check was missing in Thunderbolt XDomain property parsing. A malformed property block can make __tb_property_parse_dir() accept content_offset plus content_len beyond block_len, causing the entry parser to read past the allocated property block. For the CVSS the PR:N is used because a malicious Thunderbolt peer or device can provide malformed property data without needing a local account on the victim. The base scenario is physical access to the Thunderbolt or USB4 connection, while the paranoid scenario treats the peer as adjacent on the Thunderbolt fabric. Impact is at least denial of service via kernel crash. Limited confidentiality impact is plausible in the paranoid score because the bug is an out of bounds read, but there is no clear write primitive or supported privilege escalation path from this patch alone.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate at minimum (with actual score 3)  SKIP CVE-2026-53149  SKIP No affected files built, so skip this CVE NO  - - unknown 	MAYBE	OOB INIT SIMPLEFIX IMPROVEONLY  DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5	-	-	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=3
ActionableScoreLower=2

## 1. ActionableScore

* Conservative score: 2
* Paranoid score: 3
* Final recommended bucket: **Actionable Moderate at minimum**::

## 2. Signal breakdown

* Firmware-mediated external influence: +1
  The malformed property block is supplied through Thunderbolt / USB4 XDomain property data from an external peer or device, not by ordinary local syscall input.

* Reliable kernel crash / strong DoS: +1
  The unchecked root directory length can make the parser read past the allocated property block. This can plausibly cause a kernel fault or parser failure.

* Privileged kernel/device-management memory safety path: +1 in paranoid score
  The bug is in a trusted Thunderbolt device-management parser handling externally influenced device or peer metadata.

* Confidentiality impact plausible: +1 in paranoid score only
  This is an OOB read. Limited data exposure is theoretically possible if out-of-bounds words are interpreted as properties and later surfaced, but the patch does not show a clear disclosure primitive.

* Physical-only or rare hardware-only condition: -2
  Exploitation requires Thunderbolt / USB4 / XDomain exposure and a malicious or malformed peer/device. This is not Internet remote and not a broad default network path.

## 3. Reachability analysis

A malicious Thunderbolt / USB4 peer or device could provide a malformed root directory property block. No local account on the victim is required for that device-side input, so PR is effectively N for CVSS-style reasoning, but physical or adjacent Thunderbolt fabric access is needed.

Namespaces and containers do not materially lower or raise reachability because the affected parser is in the host kernel device-management path. The path is only relevant on systems with Thunderbolt / USB4 support and XDomain property handling, so exposure is much narrower than core networking or common local syscall APIs.

Realistic exploitation is most credible as a crash or denial of service from a malicious peripheral or peer. A stronger confidentiality outcome is possible enough to justify manual review, but not proven by the diff alone.

## 4. Severity interpretation

This behaves like an actionable Moderate issue rather than a clear Important vulnerability. The bug is a kernel OOB read on externally supplied Thunderbolt property data, so it should not be auto-closed as a trivial bounds cleanup. However, there is no OOB write, UAF, double-free, object reclaim primitive, arbitrary write, or strong LPE path shown by the patch.

The theoretical memory-safety concern is limited read past the property block. The realistic demonstrated impact is DoS. The paranoid score keeps limited confidentiality concern because OOB read bugs in parsers can sometimes become disclosure paths, but the physical/adjacent hardware requirement keeps this below a Strong Important candidate.

## 5. One-sentence report phrase

A missing root directory bounds check in Thunderbolt XDomain property parsing allows malformed peer or device supplied property data to trigger an out of bounds read past the allocated property block, with realistic impact of kernel crash and possible limited confidentiality concern.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

Reason: this is a kernel OOB read reachable from externally supplied Thunderbolt / USB4 XDomain property data. It is not clearly exploitable beyond DoS, but the external device-controlled parser input and possible limited disclosure risk make manual review appropriate.

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UPSTREAM PATCH SUMMARY
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Patch: thunderbolt: Bound root directory content to block size
Commit: 5c7657d38d07268124782f03519f07c22a5814fb
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=5c7657d38d07268124782f03519f07c22a5814fb

Commit description:

__tb_property_parse_dir() does not check that content_offset +
content_len fits within block_len for the root directory case.
When rootdir->length equals or exceeds block_len - 2, the entry
loop reads past the allocated property block.

Add a bounds check after computing content_offset and content_len
to reject directories whose content extends past the block.

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=5c7657d38d07268124782f03519f07c22a5814fb

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

The original Linux kernel CVE announcement for CVE-2026-53149 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53149

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:A/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:H
  The Best / paranoid CVSS score: 7.1

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: 2
  Paranoid ActionableScore: 3

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).