[CVE-2026-53146][MODERATE REGULAR] thunderbolt: Limit XDomain response copy to actual frame size

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

CVE: CVE-2026-53146
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: thunderbolt: Limit XDomain response copy to actual frame size
Commit: c55da494dfb445fb28df3a9d293c2be6a299cd01
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=c55da494dfb445fb28df3a9d293c2be6a299cd01
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53146
Analysis date: Mon, 29 Jun 2026 09:11:31 -0400
ActionableScore: 2
ActionableScore lower bound: 0
Actionable bucket: Ordinary Moderate / Low-like
Manual review required: NO

Summary:
A malicious Thunderbolt/USB4 XDomain peer can send a short response frame that causes tb_xdomain_copy() to copy stale DMA buffer contents past the valid frame data, resulting primarily in a physical-adjacent information disclosure risk.

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ABOUT THIS REPORT
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The original Linux kernel CVE announcement for CVE-2026-53146 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53146

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: 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-2026-53146	MODERATE	CHECK	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:L/A:L';CWE-126;*CWE-200;CWE-125;Other CVSS 'AV:P/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N';BEST CVSS score: '5.7';DESCR 'A Thunderbolt XDomain response can be shorter than the expected response size, but tb_xdomain_copy copied the expected size from the received DMA buffer. A malicious or compromised Thunderbolt/USB4 peer can send a short response and cause the local kernel to copy bytes past the valid frame data into the request response buffer. This is an out-of-bounds read relative to the received frame and may expose stale contents from previous XDomain transactions. For the CVSS the PR:N is used because the attacker does not need a local account on the victim once they can act as the connected XDomain peer. The issue is not reachable over a normal IP network and generally requires physical or directly attached Thunderbolt access. Impact is primarily information disclosure, with possible limited integrity or availability side effects depending on how the stale response data is consumed.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate / Low-like (with actual score 1) 	MAYBE	SIMPLEFIX DMAorINTERRUPT PACKET  INCREASED_FROM_LOW_BASED_ON_REQUIREMANUALCHECK DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5	-	-	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=2
ActionableScoreLower=0

## 1. ActionableScore

* Conservative score: 0
* Paranoid score: 2
* Final recommended bucket: **Ordinary Moderate / Low-like**

## 2. Signal breakdown

Conservative signals:

* Firmware-mediated or externally attached device influence: +1. A malicious or compromised Thunderbolt/USB4 XDomain peer can influence the short response frame.
* Confidentiality impact plausible: +1. The bug can copy stale bytes past the valid received frame into the response buffer.
* Physical-only or rare hardware-only condition: -2. The issue is not IP network reachable and generally requires direct Thunderbolt/USB4 peer access.

Paranoid signals:

* Firmware-mediated or externally attached device influence: +1.
* Confidentiality impact plausible: +1. Stale DMA pool contents from previous transactions may be exposed.
* Integrity or availability side effects are not strongly supported. The patch shows an over-read and stale-data copy, not an OOB write, UAF, arbitrary write, or reclaim primitive.
* Physical-only or rare hardware-only condition: -2.
* Paranoid score remains 2 because the primitive is a limited read-only over-read with physical/device adjacency.

## 3. Reachability analysis

The likely attacker is a malicious or compromised Thunderbolt/USB4 XDomain peer that can send a shorter-than-expected response frame. No local user account on the victim is required once the attacker controls the attached peer, but physical or directly attached Thunderbolt access is normally required. This is not remotely reachable over a normal network path. Containers and namespaces do not materially lower the requirement because the vulnerable input comes from the Thunderbolt XDomain transport rather than a namespace-exposed syscall API.

## 4. Severity interpretation

This behaves more like an ordinary Moderate or Low-like information disclosure issue than an Important kernel vulnerability. The demonstrated primitive is an out-of-bounds read relative to the received frame size and stale DMA buffer disclosure. There is no evidence of UAF, double-free, OOB write, attacker-controlled overwrite, page-cache corruption, or privilege escalation. The paranoid interpretation allows higher confidentiality concern if stale XDomain transaction data is sensitive, but the physical-only requirement and limited read primitive keep it below Actionable Moderate.

## 5. One-sentence report phrase

A malicious Thunderbolt/USB4 XDomain peer can send a short response frame that causes tb_xdomain_copy() to copy stale DMA buffer contents past the valid frame data, resulting primarily in a physical-adjacent information disclosure risk.

## 6. Manual review recommendation

MANUAL CHECK RECOMMENDED

Reason: this is not an Important-class candidate based on the patch alone, but it is still a kernel over-read and potential information leak on a hardware attack surface, so a lightweight manual check is appropriate to confirm whether stale response data can cross a meaningful security boundary.

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UPSTREAM PATCH SUMMARY
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Patch: thunderbolt: Limit XDomain response copy to actual frame size
Commit: c55da494dfb445fb28df3a9d293c2be6a299cd01
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=c55da494dfb445fb28df3a9d293c2be6a299cd01

Commit description:

tb_xdomain_copy() copies req->response_size bytes from the received
packet buffer regardless of the actual frame size.  When a short
response arrives, this reads past the valid frame data in the DMA
pool buffer into stale contents from previous transactions.

Use the minimum of frame size and expected response size for the
copy length.

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/xdomain.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=c55da494dfb445fb28df3a9d293c2be6a299cd01

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

The original Linux kernel CVE announcement for CVE-2026-53146 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53146

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:N/A:N
  The Best / paranoid CVSS vector: AV:P/AC:L/PR:N/UI:N/S:U/C:H/I:L/A:L
  The Best / paranoid CVSS score: 5.7

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: 0
  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: 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).