[CVE-2026-64120][LOW] net: ethtool: fix NULL pointer dereference in phy_reply_size [ Upstream

[CVE-2026-64120][LOW] net: ethtool: fix NULL pointer dereference in phy_reply_size [ Upstream

[AL-KERNEL]

CVE: CVE-2026-64120
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: net: ethtool: fix NULL pointer dereference in phy_reply_size [ Upstream
Commit: 61f53c1e58d68723bc1db10912a53f1991f08719
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=61f53c1e58d68723bc1db10912a53f1991f08719
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64120
Analysis date: Sun, 19 Jul 2026 12:27:27 -0400
ActionableScore: 1
ActionableScore lower bound: unknown
Actionable bucket: Ordinary Moderate / Low-like
Manual review required: NO

Summary:
No one-sentence report phrase was found.

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

The original Linux kernel CVE announcement for CVE-2026-64120 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64120

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: LOW
Manual review required: NO

A detailed explanation of the methodology and priority rules is included
at the end of this message.

======================================================================
AL-KERNEL CLASSIFICATION RESULT
======================================================================

CVE-2026-64120	LOW	CHECK WITH IMPACT FROM ORIG NN MODERATE	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H';CWE-252;**CWE-476;CWE-703;BEST CVSS score: '4.7';DESCR 'Unchecked kstrdup() failures in ethtool PHY reply preparation can leave rep_data string fields as NULL and later cause phy_reply_size to call strlen() on a NULL pointer. A local process that can issue the ethtool PHY_GET request could trigger this under memory pressure, causing a kernel NULL-pointer dereference and possible kernel crash. For the CVSS the PR:L is used because a local process context is required to reach the ethtool netlink control plane interface. The issue is not directly network reachable and is not triggered by packet traffic. Impact is denial of service only because the patch shows a NULL-pointer dereference path and does not indicate UAF, OOB access, arbitrary write, or information disclosure.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate / Low-like (with actual score 1)  SKIP CVE-2026-64120 UNKNOWN SKIP The Fixes patch not applied yet, so unlikely that actual: 9dd2ad5e92b962d1349a7541d167e8e214e49f95 YES  NO NO unknown 	MAYBE	DANGER NULLPTR INIT NOMEMCHK ERRORPATH UAF IMPROVEONLY  DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_GUESSCVSS_AND_CIANNH	-	-	checked

======================================================================
ACTIONABLESCORE ANALYSIS
======================================================================

ActionableScore=1

1. ActionableScore
* Conservative score: 1
* Paranoid score: 1
* Final recommended bucket: **Ordinary Moderate / Low-like**::

2. Signal breakdown
* Local unprivileged trigger: +1. A local process that can issue the ethtool PHY_GET netlink request may reach `phy_prepare_data()`.
* Reliable kernel crash / strong DoS: +1. The described failure path can lead to `strlen(NULL)` in `phy_reply_size()` and a kernel NULL pointer dereference.
* Hard or special condition required: -1. Triggering depends on `kstrdup()` allocation failure under memory pressure, not just a normal request.
* No memory corruption bonus. The patch shows unchecked allocation failure and NULL dereference, not UAF, OOB write, type confusion, double free, or arbitrary write.
* No confidentiality or integrity impact. There is no read-back leak, data overwrite, privilege boundary bypass, or file/page-cache corruption primitive.

3. Reachability analysis
The bug is reachable through the local ethtool netlink control plane, specifically PHY_GET style reporting. It is not reachable through packet traffic and is not remotely network-triggerable. In typical deployments, a local process context is required. Namespace exposure depends on whether the relevant netdevice and ethtool interface are visible inside the namespace or container. The practical trigger also requires memory allocation failure at the right point, making exploitation unreliable and primarily DoS-oriented.

Call-site confidence: high. The commit explicitly describes the downstream `phy_reply_size()` NULL dereference after unchecked `kstrdup()` failure.

4. Severity interpretation
This behaves like an ordinary Moderate or Low-like local DoS issue rather than an Important-class vulnerability. The theoretical impact is a kernel crash under memory pressure, but the patch does not support a privilege escalation, information disclosure, or corruption primitive. The main limiting factor is that allocation failure must occur during a local control-plane query.

5. One-sentence report phrase
Unchecked `kstrdup()` failures in ethtool PHY reply preparation can leave string fields NULL and cause a local `PHY_GET` request under memory pressure to trigger a NULL pointer dereference in `phy_reply_size()`, resulting in denial of service only.

6. Manual review recommendation
NO MANUAL CHECK NEEDED. This can be auto-closed or handled as deferred Moderate because the issue is a local allocation-failure NULL dereference with no supported memory corruption, confidentiality, integrity, or privilege-escalation primitive.

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

Patch: net: ethtool: fix NULL pointer dereference in phy_reply_size [ Upstream
Commit: 61f53c1e58d68723bc1db10912a53f1991f08719
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=61f53c1e58d68723bc1db10912a53f1991f08719

Changed files:
  net/ethtool/phy.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=61f53c1e58d68723bc1db10912a53f1991f08719

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

The original Linux kernel CVE announcement for CVE-2026-64120 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64120

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: Not available
  The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS score: 4.7

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: unknown
  Paranoid ActionableScore: 1

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: LOW
KPANIC detected for this report: NO
Published priority for this report (same as in Subject): LOW

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).