[CVE-2026-64000][MODERATE 7.0] net: hsr: fix potential OOB access in supervision frame handling [ Upstream

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

CVE: CVE-2026-64000
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: net: hsr: fix potential OOB access in supervision frame handling [ Upstream
Commit: 09a37dca090c55ffb1a33f52d8667f1c2367ef48
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=09a37dca090c55ffb1a33f52d8667f1c2367ef48
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64000
Analysis date: Sun, 19 Jul 2026 17:05:42 -0400
ActionableScore: 5
ActionableScore lower bound: 4
Actionable bucket: Actionable Moderate at minimum
Manual review required: YES

Summary:
A truncated HSR supervision frame can make the kernel access a TLV header before it is fully linearized in the skb, allowing an adjacent L2 attacker to trigger an OOB access and potential kernel crash on systems with exposed HSR interfaces.

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ABOUT THIS REPORT
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The original Linux kernel CVE announcement for CVE-2026-64000 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64000

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-2026-64000	MODERATE	CHECK WITH IMPACT FROM ORIG NN IMPORTANT	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:L/A:H';CWE-125;CWE-126;*CWE-20;Other CVSS 'AV:A/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '7.6';DESCR 'An out of bounds read can occur in the HSR supervision frame parser because the code may access the next TLV header before the full struct hsr_sup_tlv is present and linearized in the skb. A truncated or malformed HSR supervision frame from an adjacent Layer 2 network can reach this path and may cause a kernel crash or other availability impact. For the CVSS the PR:N because an attacker only needs adjacent network reachability to an exposed HSR interface and no local account on the target. The issue is not Internet routable in normal deployments because HSR is an Ethernet redundancy protocol used mainly in local industrial or availability focused networks. Impact is at least denial of service. In the paranoid score limited confidentiality and integrity impact is kept because the primitive is an OOB read in kernel packet parsing, but there is no evidence of OOB write or a direct privilege escalation primitive.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate at minimum (with actual score 5)	YES	OOB SIMPLEFIX NETWORK SKB LINUS KPANIC  KPANIC DECREASED_TO_MODERATE70_BASED_ON_ACTIONABLESCORELOWERTHAN7	YES	NO	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=5
ActionableScoreLower=4

## 1. ActionableScore

* Conservative score: 4
* Paranoid score: 5
* Final recommended bucket: **Actionable Moderate at minimum**::

## 2. Signal breakdown

Conservative signals:

* Remote reachable / network-triggerable: +2. The trigger is a malformed HSR supervision Ethernet frame received by an exposed HSR interface. This is adjacent L2 reachable, not Internet-routable in normal deployments.
* Reliable kernel crash / strong DoS: +1. The patch fixes a missing linearization check before dereferencing the next TLV header, and the commit explicitly states that a truncated frame could cause OOB access.
* Common packet-processing path: +1. This is in the receive-side packet parsing path for HSR supervision frames.
* Rare/configuration-dependent exposure: -1. HSR/redbox supervision handling is not a default general-purpose network path and normally exists in specialized redundancy or industrial L2 networks.
* Availability impact realistic: +1. A malformed frame can be supplied repeatedly by an adjacent attacker and may cause kernel OOB access with crash/oops potential.

Paranoid delta:

* Paranoid score removes the rare-exposure discount or treats exposed HSR industrial deployments as sufficiently security-sensitive. No strong LPE or arbitrary corruption primitive is added.

Not counted:

* No privilege escalation bonus. The patch shows OOB read/access, not UAF, OOB write, type confusion, refcount takeover, callback control, or arbitrary write.
* No strong generic memory corruption bonus. This is best classified as limited OOB read/access in packet parsing.
* No confidentiality or integrity bonus in the main score. There is no demonstrated disclosure channel or write primitive.

## 3. Reachability analysis

An attacker needs access to the same L2 segment as an HSR-enabled interface and must be able to send malformed HSR supervision frames. No local account on the target is required, so the practical PR is none once adjacent network access exists. The path is not normally exposed to the public Internet because HSR is an Ethernet redundancy protocol used mainly in industrial, high-availability, or specialized L2 environments. Containers and namespaces do not materially lower the trigger requirement unless they can transmit raw L2 frames onto the affected HSR network.

Call-site confidence: medium-high. The affected code is directly in the HSR supervision frame parser and the patch shows the missing pskb_may_pull() size adjustment immediately before TLV header access.

## 4. Severity interpretation

This behaves more like an actionable Moderate than an ordinary Moderate because it is network-triggerable from an adjacent L2 network and affects kernel packet parsing. It is not a strong Important candidate on the evidence provided because the primitive is limited OOB access/read, with no OOB write, UAF, object replacement, callback control, or demonstrated privilege escalation path. The realistic impact is DoS. The theoretical worst case justifies manual review because network-reachable OOB reads in receive paths have historically been underestimated.

## 5. One-sentence report phrase

A truncated HSR supervision frame can make the kernel access a TLV header before it is fully linearized in the skb, allowing an adjacent L2 attacker to trigger an OOB access and potential kernel crash on systems with exposed HSR interfaces.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED.
YES REQUIRES MANUAL CHECK.

Reason: adjacent-network reachable OOB access in a kernel packet receive path should not be auto-closed, even though current evidence supports DoS rather than privilege escalation.

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

Patch: net: hsr: fix potential OOB access in supervision frame handling [ Upstream
Commit: 09a37dca090c55ffb1a33f52d8667f1c2367ef48
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=09a37dca090c55ffb1a33f52d8667f1c2367ef48

Changed files:
  net/hsr/hsr_forward.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=09a37dca090c55ffb1a33f52d8667f1c2367ef48

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

The original Linux kernel CVE announcement for CVE-2026-64000 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64000

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:A/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS vector: AV:A/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:H
  The Best / paranoid CVSS score: 7.6

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: 4
  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: YES
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).