[CVE-2026-64006][MODERATE 7.0] netfilter: nf_tables: fix dst corruption in same register operation [ Upstream

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

CVE: CVE-2026-64006
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: netfilter: nf_tables: fix dst corruption in same register operation [ Upstream
Commit: b80ef316e978de2ef81d5bee9c19800b4cf96fb8
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=b80ef316e978de2ef81d5bee9c19800b4cf96fb8
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64006
Analysis date: Sun, 19 Jul 2026 19:11:11 -0400
ActionableScore: 5
ActionableScore lower bound: 2
Actionable bucket: Actionable Moderate at minimum
Manual review required: NO

Summary:
nf_tables bitwise and byteorder expressions could produce incorrect results when source and destination registers overlap, allowing crafted rulesets to alter firewall matching semantics and potentially bypass intended packet filtering policy.

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

The original Linux kernel CVE announcement for CVE-2026-64006 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64006

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: NO

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-2026-64006	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:H/A:N';CWE-682;CWE-697;*CWE-20;Other CVSS 'AV:L/AC:L/PR:H/UI:N/S:U/C:N/I:L/A:N';BEST CVSS score: '5.5';DESCR 'nf_tables bitwise shift evaluation can compute an incorrect carry when source and destination registers refer to the same storage, because the code may read a value after it has already been overwritten. Partial register overlap in bitwise or byteorder expressions can also produce incorrect expression results. This is a control plane rule semantics issue rather than kernel memory corruption. For the CVSS the PR:L is used for the paranoid score because a low privileged actor may be able to manage nftables inside a network namespace, container, or delegated firewall management context. The issue is not directly network reachable because packet traffic does not create the malformed rule by itself. Impact is primarily integrity loss of packet filtering decisions, such as unexpected match results or policy bypass in a crafted ruleset.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate at minimum (with actual score 4)	YES	REMOTE READ DANGER INIT NETFILTER LINUS TEST PACKET 	YES	NO	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=5
ActionableScoreLower=2

## 1. ActionableScore

* Conservative score: 2
* Paranoid score: 5
* Final recommended bucket: **Actionable Moderate at minimum**::

## 2. Signal breakdown

Conservative signals:

* Integrity impact plausible: +1. Incorrect nftables register results can change rule matching behavior and may cause unintended accept or drop decisions.
* Broad/default/common subsystem: +1. nf_tables is a broadly deployed firewall subsystem.
* Common packet-processing path: +1. The corrupted expression result affects packet filtering evaluation after the ruleset is installed.
* Requires CAP_NET_ADMIN in typical deployments: -2. Creating or modifying nftables bytecode normally requires administrative network privileges.

Paranoid signals:

* Local low-privileged or delegated trigger: +1. In some environments a reduced-privilege actor may control nftables through a network namespace, container setup, or delegated firewall management service.
* Security-boundary or firewall policy bypass concern: +2. The bug can alter firewall rule semantics, so a crafted or generated ruleset may fail to enforce the intended packet filtering policy.
* Integrity impact plausible: +1. The main impact is incorrect policy enforcement rather than memory corruption.
* Broad/default/common subsystem: +1. nf_tables is common in modern Linux deployments.
* Common packet-processing path: +1. The bad result is consumed by packet matching logic.
* Reduced capability penalty: -1. The issue still needs nftables rule control, but delegated CAP_NET_ADMIN or namespace-mediated control is weaker than full host root.

No memory corruption, UAF, OOB write, arbitrary write, information leak, or reliable kernel crash primitive is shown by the patch.

## 3. Reachability analysis

The bug is triggered through nf_tables control-plane rule construction, not directly by remote packets. A normal remote attacker cannot create the malformed rule by sending traffic. In typical host deployments, modifying nftables requires CAP_NET_ADMIN or root-equivalent privileges, which strongly limits exploitability.

Namespaces and containers can change the practical privilege model. If untrusted users can create user and network namespaces or if a service exposes delegated firewall rule management, the effective PR can be closer to PR:L. In that case the issue is more actionable because the attacker may be able to craft rules whose evaluation differs from the intended policy.

The path is not a rare kernel feature. nf_tables is commonly deployed, but the vulnerable condition requires specific overlapping register usage in bitwise or byteorder expressions.

## 4. Severity interpretation

This behaves like an actionable Moderate rather than an Important-class memory corruption issue. The patch fixes incorrect register semantics and rejects partial register overlap. It does not show kernel memory corruption, lifetime corruption, object reuse, or a crash path.

The realistic impact is firewall integrity degradation in crafted or generated nftables rulesets. The theoretical risk is that incorrect expression results can bypass intended filtering policy, especially when rule generation is delegated or constrained by a higher-level security model. That justifies manual review, but not Important-class treatment absent a concrete memory corruption or privilege escalation primitive.

## 5. One-sentence report phrase

nf_tables bitwise and byteorder expressions could produce incorrect results when source and destination registers overlap, allowing crafted rulesets to alter firewall matching semantics and potentially bypass intended packet filtering policy.

## 6. Manual review recommendation

MANUAL CHECK RECOMMENDED

Manual review is recommended because this is a firewall policy integrity issue in a common packet-filtering subsystem, even though the patch does not indicate memory corruption or direct remote exploitation.

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

Patch: netfilter: nf_tables: fix dst corruption in same register operation [ Upstream
Commit: b80ef316e978de2ef81d5bee9c19800b4cf96fb8
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=b80ef316e978de2ef81d5bee9c19800b4cf96fb8

Changed files:
  include/net/netfilter/nf_tables.h
  net/netfilter/nft_bitwise.c
  net/netfilter/nft_byteorder.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=b80ef316e978de2ef81d5bee9c19800b4cf96fb8

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

The original Linux kernel CVE announcement for CVE-2026-64006 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64006

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:L/PR:H/UI:N/S:U/C:N/I:L/A:N
  The Best / paranoid CVSS vector: AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:H/A:N
  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: 2
  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).