[CVE-2026-74260][MODERATE REGULAR] netfilter: nf_dup_netdev: add nf_dev_xmit_recursion*() helpers and use them [ Upstream

[CVE-2026-74260][MODERATE REGULAR] netfilter: nf_dup_netdev: add nf_dev_xmit_recursion*() helpers and use them [ Upstream

[AL-KERNEL]

CVE: CVE-2026-74260
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: netfilter: nf_dup_netdev: add nf_dev_xmit_recursion*() helpers and use them [ Upstream
Commit: edf234f71fb327792196f813048ab8f5bd3bb712
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=edf234f71fb327792196f813048ab8f5bd3bb712
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74260
Analysis date: Sat, 15 Aug 2026 05:30:03 -0400
ActionableScore: 4
ActionableScore lower bound: 3
Actionable bucket: Borderline, manual review recommended / Actionable Moderate only in exposed nft_dup or nft_fwd deployments
Manual review required: YES

Summary:
No one-sentence report phrase was found.

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

The original Linux kernel CVE announcement for CVE-2026-74260 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74260

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-2026-74260	MODERATE	CHECK WITH IMPACT FROM ORIG NN MODERATE	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H';CWE-362;CWE-667;**CWE-400;Other CVSS 'AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '5.9';DESCR 'nft_dup and nft_fwd used a per CPU recursion counter around skb transmit, but the increment and decrement could become imbalanced if execution migrated to another CPU during dev_queue_xmit or neigh_xmit. This can corrupt recursion accounting for NF_RECURSION_LIMIT and may cause unexpected packet drops, persistent forwarding degradation, or denial of service in systems that use netdev nft_dup or nft_fwd rules. For the CVSS the PR:N is used for the paranoid score because packet traffic can trigger the data path when vulnerable nft_dup or nft_fwd rules already exist, without an account on the target. The issue is network reachable only in deployments where attacker controlled packets can hit these netfilter netdev rules. Impact is denial of service only. No concrete UAF, OOB write, info leak, or privilege escalation primitive is evident from the code change. For the paranoid score, choose the highest still defensible DoS interpretation supported by the bug class and patch context, with preference for manual review sensitivity over autoclosed false negatives.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline, manual review recommended / Actionable Moderate only in exposed nft_dup or nft_fwd deployments (with actual score 4)  SKIP CVE-2026-74260 UNKNOWN SKIP The Fixes patch not applied yet, so unlikely that actual: 1d47b55b36d2ec73fe6901212c8b28a593c3b27c YES  NO NO unknown 	MAYBE	REMOTE OOB NETFILTER SKB HARDWARE  DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5	-	-	checked

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

ActionableScore=4
ActionableScoreLower=3

1. ActionableScore
* Conservative score: 3
* Paranoid score: 4
* Final recommended bucket: **Borderline, manual review recommended / Actionable Moderate only in exposed nft_dup or nft_fwd deployments**::

2. Signal breakdown
* Remote reachable / network-triggerable: +2. Attacker controlled packets can reach the affected data path if vulnerable nft_dup or nft_fwd netdev rules already exist.
* Common networking core path or packet-processing path: +1. The bug is in netfilter packet forwarding or duplication paths.
* Reliable kernel crash / strong DoS: +1 for paranoid only. The patch context supports packet drops or forwarding degradation from imbalanced recursion accounting, but not memory corruption.
* Availability impact realistic: +1 for paranoid only. A stuck or imbalanced recursion counter can plausibly cause persistent packet drops on affected paths.
* Hard or unreliable race / special timing required: -1. The problematic condition depends on CPU migration during transmit.
* No memory corruption signal. The patch does not show UAF, OOB write, double free, type confusion, stale callback, or attacker controlled overwrite.
* No privilege escalation signal. The visible primitive is recursion accounting corruption and DoS only.

3. Reachability analysis
The trigger is packet traffic through configured nft_dup or nft_fwd netdev rules. Creating such rules normally requires CAP_NET_ADMIN, but once the rules are installed, packet injection may require no local account on the target. Namespaces can lower setup requirements only if an attacker controls a network namespace with relevant nftables permissions, but host impact then depends on how the rules and devices are exposed. This is not a default universal path because it requires specific netfilter rules, but netfilter is common and the affected path is packet-facing when configured.

4. Severity interpretation
This behaves more like a borderline Moderate networking DoS than an Important memory-corruption issue. The theoretical worst case is sustained forwarding degradation or packet drops due to broken recursion accounting. Realistic exploitation evidence does not support LPE, confidentiality impact, integrity impact, or kernel code execution.

5. One-sentence report phrase
A CPU migration race in netfilter nft_dup and nft_fwd transmit recursion accounting can imbalance per CPU counters and cause packet drops or denial of service when attacker controlled traffic reaches affected netdev rules.

6. Manual review recommendation
MANUAL CHECK RECOMMENDED. This is packet-path netfilter code and may be remotely triggerable in configured deployments, but the patch supports DoS only and does not show a concrete memory corruption or privilege escalation primitive.

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

Patch: netfilter: nf_dup_netdev: add nf_dev_xmit_recursion*() helpers and use them [ Upstream
Commit: edf234f71fb327792196f813048ab8f5bd3bb712
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=edf234f71fb327792196f813048ab8f5bd3bb712

Changed files:
  include/net/netfilter/nf_dup_netdev.h
  net/netfilter/nf_dup_netdev.c
  net/netfilter/nft_fwd_netdev.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=edf234f71fb327792196f813048ab8f5bd3bb712

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

The original Linux kernel CVE announcement for CVE-2026-74260 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74260

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:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:L
  The Best / paranoid CVSS vector: AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS score: 5.9

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).