[CVE-2026-64077][MODERATE 7.0] netfilter: ebtables: move to two-stage removal scheme [ Upstream

[CVE-2026-64077][MODERATE 7.0] netfilter: ebtables: move to two-stage removal scheme [ Upstream

[AL-KERNEL]

CVE: CVE-2026-64077
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: netfilter: ebtables: move to two-stage removal scheme [ Upstream
Commit: 739d5dac7b2da44a756aa4d758ee3f1ccf5a27f1
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=739d5dac7b2da44a756aa4d758ee3f1ccf5a27f1
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64077
Analysis date: Sun, 19 Jul 2026 12:10:51 -0400
ActionableScore: 5
ActionableScore lower bound: 3
Actionable bucket: Actionable Moderate at minimum
Manual review required: YES

Summary:
An ebtables table lifecycle race can expose partially initialized or stale table state during netfilter hook registration and teardown, allowing at least local DoS and requiring manual review for possible lifetime-corruption impact.

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

The original Linux kernel CVE announcement for CVE-2026-64077 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64077

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
======================================================================

CVE-2026-64077	MODERATE	CHECK WITH IMPACT FROM ORIG NN LOW	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H';CWE-362;*CWE-416;CWE-665;CWE-667;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '7';DESCR 'ebtables table registration and teardown can expose an inconsistent table lifetime state. A table could be visible before table ops are fully assigned, and removal could race with hook unregister and later cleanup. This can lead to a local denial of service and is a plausible lifetime race candidate for use after free style behavior during netfilter control plane operations. For the CVSS the PR:L is used in the paranoid score because reliable triggering may be possible for a local actor with CAP_NET_ADMIN or delegated network administration rights, including container root or a service account with reduced capabilities. The issue is not directly network reachable and is not triggered by normal packet traffic. Impact is at least availability loss through crash or warning. In the paranoid interpretation, confidentiality and integrity are also considered because stale or partially initialized table state can be a memory lifetime hazard and should be reviewed manually.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate at minimum (with actual score 4)  SKIP CVE-2026-64077 UNKNOWN SKIP The Fixes patch not applied yet, so unlikely that actual: 87663c39f898b18905499126548da61450628682 YES  NO NO unknown 	MAYBE	LOCK INIT NETFILTER LOG  INCREASED_TO_MODERATE_FROM_LOW_BASED_ON_GUESSCVSS DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5	-	-	checked

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

ActionableScore=5
ActionableScoreLower=3

## 1. ActionableScore

* Conservative score: 3
* Paranoid score: 5
* Final recommended bucket: **Actionable Moderate at minimum**::

## 2. Signal breakdown

Conservative signals:

* Weak/indirect corruption candidate: +1. The patch prevents exposure of a partially initialized `ebt_table` and changes teardown ordering around `table->ops`, hook unregister, and final cleanup.
* Real lifetime corruption concern: +1. The new `dead_tables` list and two-stage removal scheme indicate an object lifetime/order issue around netfilter hook unregister and table destruction.
* Reliable crash / strong DoS concern: +1. A stale or partially initialized table reachable during register/unregister can plausibly cause kernel crash, WARN, or broken hook/table state.
* Broad/default/common subsystem: +1. Netfilter/ebtables is not a rare hardware-only path, although this is bridge/ebtables control plane rather than the central packet fast path.
* Requires CAP_NET_ADMIN or equivalent in typical deployments: -1. Full `-2` is not applied because CAP_NET_ADMIN may be delegated to containers, user namespaces, or reduced-capability service contexts.

Paranoid additional interpretation:

* Local unprivileged or reduced-privilege trigger possible in some configurations: +1. If unprivileged user namespaces or containerized CAP_NET_ADMIN are available, a non-host-root actor may exercise the ebtables/netns lifecycle path.
* Weak LPE concern: +1. This is not a strong LPE primitive, but partial object publication plus lifetime teardown around netfilter hooks is enough to require manual review for stale object misuse or controlled corruption sinks.

Not awarded:

* No remote/network-triggerable score. This is not triggered by packet traffic alone.
* No strong memory corruption score. The patch does not show attacker-controlled reclaim, arbitrary write, callback control, or type confusion.
* No Dirty-Pipe-like/page-cache signal.
* No strong Important score because practical exploitation beyond DoS is not demonstrated.

## 3. Reachability analysis

The likely trigger is local control-plane activity involving ebtables table registration, module or template unregister, net namespace teardown, or bridge netfilter setup and cleanup. In a normal host configuration this generally requires CAP_NET_ADMIN or administrative control. In containerized environments, reduced-capability root or a service with delegated CAP_NET_ADMIN may be enough, so treating this strictly as full PR:H would understate practical exposure.

The affected path is not directly reachable from remote packets. Packet traffic may interact with registered hooks, but the vulnerable condition is the table lifecycle transition itself. Exploitation conditions are realistic for local or namespace-capable attackers who can repeatedly create and tear down netfilter state, but the race/lifetime window still needs careful validation.

Call-site confidence: high, because the patch includes the relevant register, pre-exit unregister, final unregister, and pernet teardown paths.

## 4. Severity interpretation

This behaves more like an actionable Moderate than an ordinary Low/Moderate cleanup. The realistic demonstrated impact is local DoS or kernel instability from inconsistent ebtables table lifecycle state. The theoretical concern is memory lifetime corruption because a table can be visible before `ops` is fully assigned, and unregister/cleanup ordering could leave stale table state around hook removal.

It is not a strong Important candidate without additional evidence of attacker-controlled object reuse, write-after-free, callback dispatch, type confusion, or privilege escalation. However, because this is a netfilter lifetime/race fix with partially initialized object exposure, it should not be auto-closed without review.

## 5. One-sentence report phrase

An ebtables table lifecycle race can expose partially initialized or stale table state during netfilter hook registration and teardown, allowing at least local DoS and requiring manual review for possible lifetime-corruption impact.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

Manual review is required because the patch fixes netfilter hook/table lifetime ordering and partial object exposure. The conservative impact is DoS, but the object lifetime pattern is sufficiently sensitive that stale pointer or UAF-style consequences should be checked before closure.

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

Patch: netfilter: ebtables: move to two-stage removal scheme [ Upstream
Commit: 739d5dac7b2da44a756aa4d758ee3f1ccf5a27f1
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=739d5dac7b2da44a756aa4d758ee3f1ccf5a27f1

Changed files:
  net/bridge/netfilter/ebtable_broute.c
  net/bridge/netfilter/ebtable_filter.c
  net/bridge/netfilter/ebtable_nat.c
  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=739d5dac7b2da44a756aa4d758ee3f1ccf5a27f1

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

The original Linux kernel CVE announcement for CVE-2026-64077 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64077

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:L/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:H/I:H/A:H
  The Best / paranoid CVSS score: 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: 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).