[CVE-2026-64076][MODERATE REGULAR] netfilter: bridge: eb_tables: close module init race [ Upstream

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

CVE: CVE-2026-64076
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: netfilter: bridge: eb_tables: close module init race [ Upstream
Commit: c647e2a21bbbaceda6cdb8a44a56f44d231dc4b4
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=c647e2a21bbbaceda6cdb8a44a56f44d231dc4b4
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64076
Analysis date: Sun, 19 Jul 2026 22:39:31 -0400
ActionableScore: 3
ActionableScore lower bound: 1
Actionable bucket: Borderline, manual review recommended
Manual review required: YES

Summary:
An ebtables module initialization race exposed sockopts before per-network state was registered, allowing a local CAP_NET_ADMIN-capable process racing module load to plausibly trigger invalid state access and a kernel crash.

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

The original Linux kernel CVE announcement for CVE-2026-64076 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64076

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.

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

CVE-2026-64076	MODERATE	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-362;CWE-665;**CWE-476;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '4.7';DESCR 'ebtables module initialization exposed the nf_register_sockopt interface before the per network ebtables state was registered. A local process racing against module load could reach the ebtables sockopt path while required pernet state is not fully initialized, which can plausibly cause a NULL pointer dereference and kernel crash. For the CVSS the PR:L is used in the paranoid score because some deployments allow less trusted users or containerized workloads to obtain delegated CAP_NET_ADMIN in a network namespace. The issue is not directly network reachable and is triggered through local control plane sockopt operations rather than bridge packet traffic. Impact is denial of service via kernel crash, with no strong evidence of confidentiality or integrity impact from the patch context.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline, manual review recommended (with actual score 2)	YES	INIT SIMPLEFIX NETFILTER RACE 	YES	NO	checked

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

ActionableScore=3
ActionableScoreLower=1

## 1. ActionableScore

* Conservative score: 1
* Paranoid score: 3
* Final recommended bucket: **Borderline, manual review recommended**

## 2. Signal breakdown

Conservative signals:

* Weak/indirect corruption candidate: +1. The race can expose the ebtables sockopt path before pernet state is registered, plausibly causing invalid or NULL pernet state access.
* Reliable kernel crash / strong DoS: +1. The likely failure mode is kernel crash or Oops from using incompletely initialized state.
* Broad/default/common subsystem: +1. Netfilter is broadly deployed, although this is ebtables bridge control-plane init rather than the common packet fast path.
* Hard or unreliable race / special timing required: -1. The attacker must race a narrow module initialization window.
* Requires admin/root/CAP_NET_ADMIN in typical deployments: -2. Practical triggering normally requires local netfilter control privileges and module-load timing.

Paranoid adjustment:

* Local delegated trigger concern: +1. In some namespace/container setups, delegated CAP_NET_ADMIN or reduced-privilege network administration may make the trigger less than full host-root.
* Capability penalty reduced in paranoid view. This is not treated as full host-root if the affected environment gives reduced-capability users access to network namespace administration.

## 3. Reachability analysis

The bug is local control-plane reachable through ebtables sockopt operations during module initialization. It is not directly network reachable and is not triggered by bridge packet traffic alone. In typical deployments, modifying ebtables requires CAP_NET_ADMIN and the race also requires timing against module load, which makes reliable exploitation difficult. Namespaces can matter if untrusted users can obtain delegated CAP_NET_ADMIN in a network namespace or can indirectly trigger module loading, but this is deployment-dependent.

Call-site confidence: medium. The changed code clearly reorders module initialization so nf_register_sockopt() is last, but the exact downstream dereference path is not shown in the provided patch.

## 4. Severity interpretation

This behaves like a borderline Moderate issue, not an Important-class vulnerability. The patch indicates an initialization race with possible invalid state access and DoS, but it does not show attacker-controlled reclaim, write-after-free, type confusion, callback control, arbitrary write, or a practical privilege escalation path. The theoretical concern is incomplete initialization leading to invalid object access, while the realistic impact is local kernel crash under a narrow timing window.

## 5. One-sentence report phrase

An ebtables module initialization race exposed sockopts before per-network state was registered, allowing a local CAP_NET_ADMIN-capable process racing module load to plausibly trigger invalid state access and a kernel crash.

## 6. Manual review recommendation

MANUAL CHECK RECOMMENDED.

This is not strong enough for Important by itself, but it is a race in netfilter initialization with plausible kernel crash behavior and namespace-dependent privilege interpretation, so it should not be blindly auto-closed without confirming product exposure.

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

Patch: netfilter: bridge: eb_tables: close module init race [ Upstream
Commit: c647e2a21bbbaceda6cdb8a44a56f44d231dc4b4
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=c647e2a21bbbaceda6cdb8a44a56f44d231dc4b4

Changed files:
  net/bridge/netfilter/ebtables.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=c647e2a21bbbaceda6cdb8a44a56f44d231dc4b4

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

The original Linux kernel CVE announcement for CVE-2026-64076 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64076

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:L/AC:H/PR:H/UI:N/S:U/C:N/I:N/A:H
  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: 1
  Paranoid ActionableScore: 3

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).