[CVE-2026-63986][MODERATE REGULAR] ethtool: tsinfo: don't pass ERR_PTR to genlmsg_cancel on prepare failure [ Upstream

[CVE-2026-63986][MODERATE REGULAR] ethtool: tsinfo: don't pass ERR_PTR to genlmsg_cancel on prepare failure [ Upstream

[AL-KERNEL]

CVE: CVE-2026-63986
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: ethtool: tsinfo: don't pass ERR_PTR to genlmsg_cancel on prepare failure [ Upstream
Commit: 2008f9bb1ede9b688624a241228b8e54fc74f0f6
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=2008f9bb1ede9b688624a241228b8e54fc74f0f6
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-63986
Analysis date: Sun, 19 Jul 2026 12:30:35 -0400
ActionableScore: 4
ActionableScore lower bound: 3
Actionable bucket: Borderline Moderate. Manual review recommended
Manual review required: YES

Summary:
An ethtool tsinfo generic netlink dump error path can pass an ERR_PTR to genlmsg_cancel() after prepare failure, allowing a local user able to issue the query to crash the kernel.

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

The original Linux kernel CVE announcement for CVE-2026-63986 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-63986

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.

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

CVE-2026-63986	MODERATE	CHECK WITH IMPACT FROM ORIG NN MODERATE	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H';CWE-754;CWE-252;**CWE-476;BEST CVSS score: '5.5';DESCR 'An ethtool tsinfo dump error path can pass an ERR_PTR value to genlmsg_cancel when ethnl_tsinfo_prepare_dump fails before a generic netlink message has been started. This can crash the kernel because genlmsg_cancel expects a valid message header, not an encoded error pointer. For the CVSS the PR:L is used because triggering requires a local process able to issue the ethtool netlink dump request, but not necessarily full administrative control in typical read-only query paths. The issue is not network reachable through packet traffic and is a local control plane bug. Impact is denial of service via kernel crash, with no supported confidentiality or integrity impact from the patch context.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline Moderate. Manual review recommended (with actual score 4)	YES	DANGER SIMPLEFIX LINUS  DECREASED_TO_MODERATE_REGULAR_FROM_MODERATE7_BASED_ON_GUESSCVSS_AND_CIANNH	YES	NO	checked

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

ActionableScore=4
ActionableScoreLower=3

## 1. ActionableScore

* Conservative score: 3
* Paranoid score: 4
* Final recommended bucket: **Borderline Moderate. Manual review recommended**

## 2. Signal breakdown

* Local unprivileged trigger: +1
  The affected path is an ethtool generic netlink dump path. Read-only ethtool query paths are commonly reachable by a local process without full administrative privileges.

* Reliable kernel crash / strong DoS: +1
  The commit explicitly states that passing an ERR_PTR to genlmsg_cancel() would cause a crash.

* Broad/default/common subsystem exposure: +1
  ethtool netlink is a broadly available networking control-plane interface, although this is not packet-triggered.

* Paranoid availability confidence: +1
  If ethnl_tsinfo_prepare_dump() failure can be triggered reliably through dump sizing, device topology, or allocation pressure, the result is a local kernel crash. This raises the practical triage score to 4.

No memory corruption score is added. The primitive is an invalid error-pointer dereference, not UAF, OOB write, double free, type confusion, or attacker-controlled overwrite.

## 3. Reachability analysis

A local process able to issue ethtool netlink tsinfo dump requests can reach this path. It does not appear to require network packet delivery or remote access. CAP_NET_ADMIN is not clearly required for a read-only dump-style ethtool query, so PR:L is the safer practical interpretation. Namespaces may matter if ethtool netlink access to devices is exposed inside a network namespace, but the bug remains local control-plane reachable rather than remotely packet-triggerable.

The main uncertainty is whether the prepare failure is easy to force under normal conditions or mostly depends on memory pressure or unusual topology. That uncertainty keeps the conservative score below Actionable Moderate.

## 4. Severity interpretation

This behaves like a local Moderate DoS issue, not an Important-class vulnerability. The patch supports a kernel crash scenario through invalid ERR_PTR handling, but does not support confidentiality impact, integrity impact, privilege escalation, or a strong memory-corruption primitive. Theoretical exploitation beyond DoS is not justified from the patch context.

## 5. One-sentence report phrase

An ethtool tsinfo generic netlink dump error path can pass an ERR_PTR to genlmsg_cancel() after prepare failure, allowing a local user able to issue the query to crash the kernel.

## 6. Manual review recommendation

MANUAL CHECK RECOMMENDED

Reason: local netlink-reachable kernel crash paths should be checked manually for actual trigger reliability, required privileges, and whether the prepare failure can be induced without artificial memory pressure.

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

Patch: ethtool: tsinfo: don't pass ERR_PTR to genlmsg_cancel on prepare failure [ Upstream
Commit: 2008f9bb1ede9b688624a241228b8e54fc74f0f6
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=2008f9bb1ede9b688624a241228b8e54fc74f0f6

Changed files:
  net/ethtool/tsinfo.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=2008f9bb1ede9b688624a241228b8e54fc74f0f6

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

The original Linux kernel CVE announcement for CVE-2026-63986 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-63986

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:L/PR:L/UI:N/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS score: 5.5

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: 4

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).