[CVE-2026-53147][MODERATE 7.0] thunderbolt: Validate XDomain request packet size before type cast

[CVE-2026-53147][MODERATE 7.0] thunderbolt: Validate XDomain request packet size before type cast

[AL-KERNEL]

CVE: CVE-2026-53147
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: thunderbolt: Validate XDomain request packet size before type cast
Commit: a770e62923090d7572f1f5a8507ae551d354a057
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=a770e62923090d7572f1f5a8507ae551d354a057
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53147
Analysis date: Fri, 26 Jun 2026 04:10:55 -0400
ActionableScore: 5
ActionableScore lower bound: 2
Actionable bucket: Actionable Moderate at minimum
Manual review required: YES

Summary:
A malicious Thunderbolt or USB4 XDomain peer can send a short request packet that passes generic validation but is smaller than the protocol-specific structure later accessed, causing an out-of-bounds kernel read with possible limited information exposure or host DoS.

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ABOUT THIS REPORT
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The original Linux kernel CVE announcement for CVE-2026-53147 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53147

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-2026-53147	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:L/I:N/A:L';BEST CVSS score: '7.1';DESCR 'Thunderbolt XDomain request handling can read past the end of a received kmemdup packet because tb_xdp_handle_request casts the buffer to protocol specific request structures before verifying that the packet is large enough. A malicious XDomain peer can send a minimal packet that passes the generic header length check but is shorter than the structure accessed after the cast, causing an out of bounds kernel read. For the CVSS the PR:N is used because the peer does not need a local user account on the victim once it can send XDomain packets. The base score treats the attack as physical access to a Thunderbolt port, while the paranoid score treats an already connected Thunderbolt or USB4 peer as adjacent. Impact is at least denial of service or limited confidentiality exposure from an invalid kernel read, with no clear evidence of an OOB write or privilege escalation primitive.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate at minimum (with actual score 4)  SKIP CVE-2026-53147  SKIP No affected files built, so skip this CVE NO  - - unknown 	MAYBE	READ DANGER SIMPLEFIX IMPROVEONLY PACKET  INCREASED_TO_MODERATE7_FROM_MODERATE_BASED_ON_GUESSCVSS DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5	-	-	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=5
ActionableScoreLower=2

## 1. ActionableScore

* Conservative score: 2
* Paranoid score: 5
* Final recommended bucket: **Actionable Moderate at minimum**::

## 2. Signal breakdown

Paranoid score signals:

* Firmware-mediated external influence: +1
  A malicious Thunderbolt or USB4 XDomain peer can influence the packet contents processed by the host kernel.
* Privileged kernel/device-management path: +1
  The bug is in the Thunderbolt XDomain control path, a trusted kernel device-management subsystem processing peer supplied protocol data.
* Reliable kernel crash / strong DoS: +1
  The malformed packet can drive out-of-bounds reads in kernel request handling. A host-wide crash is plausible depending on slab layout, debug options, and accessed fields.
* Confidentiality impact plausible: +1
  The primitive is an out-of-bounds kernel read from a kmemdup allocation. There is no proven disclosure channel in the patch, but limited adjacent-memory exposure is plausible.
* Availability impact realistic: +1
  A malformed peer packet can plausibly destabilize the kernel or cause an oops, especially because this is asynchronous workqueue processing in a hardware protocol path.

Conservative deductions:

* Physical-only or rare hardware-only condition: -2
  In the conservative model, the attacker needs physical access to a Thunderbolt port or control of an attached Thunderbolt or USB4 peer device.

Not counted:

* Remote reachable / network-triggerable: +0
  This is not Internet or normal network reachable.
* Local unprivileged trigger: +0
  No local user account is needed, but the trigger is not a normal local syscall interface.
* Generic memory corruption: +0
  The patch supports OOB read only, not OOB write, UAF, double-free, or controlled overwrite.
* Privilege escalation plausible: +0
  No realistic LPE primitive is demonstrated.
* Real lifetime corruption: +0
  No lifetime, refcount, RCU, or stale pointer issue is shown.

## 3. Reachability analysis

The bug can be triggered by a malicious Thunderbolt or USB4 XDomain peer that can send a short request packet passing the generic header validation but shorter than the protocol-specific structure later accessed. This does not require a local user account on the victim host, but it does require physical or adjacent-device reachability to the Thunderbolt fabric.

Namespaces and containers do not materially lower or raise privileges here because the affected path is not a namespace-scoped local API. The practical exposure depends on hardware presence, Thunderbolt/USB4 support, and whether an attacker can attach or control a peer device. This is not a default Internet-facing attack surface.

## 4. Severity interpretation

This behaves above an ordinary Moderate issue because it is peer-triggered kernel OOB read in a hardware control protocol. It is not a strong Important candidate on current evidence because the primitive is read-only and the patch does not show UAF, OOB write, arbitrary write, reclaim control, or a clear privilege escalation path.

The realistic impact is limited confidentiality exposure and possible DoS. The paranoid score treats the peer as adjacent rather than purely physical and assumes the OOB read can produce a host-visible crash, making it Actionable Moderate and not suitable for automatic closure without review.

## 5. One-sentence report phrase

A malicious Thunderbolt or USB4 XDomain peer can send a short request packet that passes generic validation but is smaller than the protocol-specific structure later accessed, causing an out-of-bounds kernel read with possible limited information exposure or host DoS.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

Reason: this is a peer-reachable kernel OOB read in a hardware control protocol. The current evidence does not justify LPE or strong memory corruption scoring, but the adjacent-device attack model and possible kernel memory exposure make automatic closure risky.

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

Patch: thunderbolt: Validate XDomain request packet size before type cast
Commit: a770e62923090d7572f1f5a8507ae551d354a057
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=a770e62923090d7572f1f5a8507ae551d354a057

Commit description:

tb_xdp_handle_request() casts the received packet buffer to
protocol-specific structs without verifying that the allocation
is large enough for the target type.  A peer can send a minimal
XDomain packet that passes the generic header length check but is
shorter than the struct accessed after the cast, causing out-of-
bounds reads from the kmemdup allocation.

Plumb the packet length through xdomain_request_work and validate
it against the expected struct size before each cast.

Fixes: 8e1de70 ("thunderbolt: Add support for XDomain lane bonding")
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=a770e62923090d7572f1f5a8507ae551d354a057

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

The original Linux kernel CVE announcement for CVE-2026-53147 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53147

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:L
  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: 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: NO
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).