[CVE-2026-74585][MODERATE 7.0] thunderbolt: Bound the DROM dual link port number before indexing sw->ports

[CVE-2026-74585][MODERATE 7.0] thunderbolt: Bound the DROM dual link port number before indexing sw->ports

[AL-KERNEL]

CVE: CVE-2026-74585
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: thunderbolt: Bound the DROM dual link port number before indexing sw->ports
Commit: 6c892ed9f4129ae40ef0f92e1bb31aa0b0ddc72c
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=6c892ed9f4129ae40ef0f92e1bb31aa0b0ddc72c
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74585
Analysis date: Sat, 22 Aug 2026 17:47:53 -0400
ActionableScore: 5
ActionableScore lower bound: 3
Actionable bucket: Strong Important candidate / Actionable Moderate at minimum
Manual review required: YES

Summary:
A malicious Thunderbolt device can provide an out-of-range DROM dual_link_port_nr value that creates an out-of-bounds tb_port pointer which is stored and later dereferenced, making kernel crash realistic and limited memory-corruption impact plausible.

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ABOUT THIS REPORT
======================================================================

The original Linux kernel CVE announcement for CVE-2026-74585 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74585

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-2026-74585	MODERATE	CHECK WITH IMPACT FROM ORIG NN IMPORTANT	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:H/A:H';CWE-129;CWE-823;*CWE-787;Other CVSS 'AV:P/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:H';BEST CVSS score: '6.8';DESCR 'A malicious or malformed Thunderbolt device can provide a DROM port entry where dual_link_port_nr is larger than the allocated sw ports array. The unchecked value is used to build an out-of-bounds tb_port pointer and that pointer can be stored and later dereferenced by the Thunderbolt driver. This is a physical attack surface, not a network reachable issue. For the CVSS the PR:N is used because the attacker does not need local credentials on the victim system and only needs the ability to present a crafted Thunderbolt device. Impact is at least denial of service via kernel crash and may include confidentiality or integrity impact because the bug creates an out-of-bounds kernel object pointer that can be used after parsing.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 4)	YES	WRITE OOB SIMPLEFIX HARDWARE  DECREASED_TO_MODERATE70_BASED_ON_ACTIONABLESCORELOWERTHAN6 DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5	NO	NO	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=5
ActionableScoreLower=3

## 1. ActionableScore

* Conservative score: 3
* Paranoid score: 5
* Final recommended bucket: **Strong Important candidate / Actionable Moderate at minimum**::

## 2. Signal breakdown

Conservative signals:

* Firmware-mediated external influence: +1. The malformed value is supplied by a Thunderbolt device DROM rather than by a local syscall or network packet.
* Memory corruption, Weak/indirect corruption candidate: +1. The unchecked DROM field is used as an index into sw->ports and creates an out-of-bounds tb_port pointer.
* Reliable kernel crash / strong DoS: +1. The commit states that the out-of-bounds pointer is stored and later dereferenced.
* Privileged kernel/device-management memory corruption path: +1. The corruption occurs in Thunderbolt device enumeration and trusted kernel device-management state.
* Physical-only or rare hardware-only condition: -2. Triggering requires presenting a malicious or malformed Thunderbolt device or equivalent device-level control.

Paranoid additional signals:

* Weak LPE concern: +1. The bug stores a bogus kernel object pointer that may later be interpreted as a valid struct tb_port, but no controlled overwrite or reclaim primitive is shown.
* Confidentiality impact plausible: +1. Later dereference of an out-of-bounds object pointer could potentially read adjacent kernel object fields.
* Integrity impact plausible: +1. Later use of the bogus tb_port pointer could potentially update fields through an invalid object interpretation.
* No strong memory corruption primitive is awarded. The patch shows an unchecked object index and stored OOB pointer, not an attacker-controlled write, UAF reclaim, double free, or arbitrary write.

## 3. Reachability analysis

The bug is triggerable by a malicious or malformed Thunderbolt device that supplies a DROM port entry with dual_link_port_nr greater than sw->config.max_port_number. No local OS credentials are required on the victim, but physical device access or equivalent hardware-level control is required. Namespaces and containers do not materially change reachability because this is a hardware enumeration path, not a local userspace API. The path is relevant on systems with Thunderbolt support enabled and a reachable Thunderbolt port. Realistic exploitation is constrained by physical access, Thunderbolt security policy, and platform DMA/device authorization settings, but malformed device parsing before or during enumeration is still a meaningful attack surface.

## 4. Severity interpretation

This is stronger than an ordinary Moderate correctness issue because the patch fixes an unchecked device-supplied index that creates a persistent out-of-bounds kernel object pointer. Realistic demonstrated impact is most clearly kernel crash or device-management state corruption. Theoretical impact may extend to confidentiality or integrity if later code reads or writes through the bogus tb_port pointer, but the patch does not demonstrate a controlled overwrite, type-confusion exploit, or practical privilege escalation chain. Overall this should be treated as Actionable Moderate and manually reviewed, with an Important-candidate concern only under the paranoid interpretation.

## 5. One-sentence report phrase

A malicious Thunderbolt device can provide an out-of-range DROM dual_link_port_nr value that creates an out-of-bounds tb_port pointer which is stored and later dereferenced, making kernel crash realistic and limited memory-corruption impact plausible.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

Reason: the issue is device-supplied OOB kernel object selection with later dereference in a privileged Thunderbolt enumeration path, and the practical impact depends on how the stored tb_port pointer is used by follow-on call sites.

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

Patch: thunderbolt: Bound the DROM dual link port number before indexing sw->ports
Commit: 6c892ed9f4129ae40ef0f92e1bb31aa0b0ddc72c
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=6c892ed9f4129ae40ef0f92e1bb31aa0b0ddc72c

Commit description:

tb_drom_parse_entry_port() validates the device-supplied header->index
against sw->config.max_port_number before indexing sw->ports[], but the
sibling field entry->dual_link_port_nr -- a 6-bit value also read from
the DROM -- indexes the same array with no such check. A malicious or
malformed Thunderbolt device can set dual_link_port_nr beyond the
allocated sw->ports[] (max_port_number + 1 entries), producing an
out-of-bounds tb_port pointer that is stored and later dereferenced.

Reject a port entry whose dual_link_port_nr exceeds max_port_number,
the same bound already applied to header->index.

Fixes: cd22e73 ("thunderbolt: Read port configuration from eeprom.")
Cc: stable@vger.kernel.org
Signed-off-by: Bryam Vargas <hexlabsecurity@proton.me>
Signed-off-by: Mika Westerberg <mika.westerberg@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  drivers/thunderbolt/eeprom.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=6c892ed9f4129ae40ef0f92e1bb31aa0b0ddc72c

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

The original Linux kernel CVE announcement for CVE-2026-74585 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74585

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:P/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
  The Best / paranoid CVSS score: 6.8

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: 3
  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).