[CVE-2026-72419][MODERATE 7.0] netfilter: nf_nat: avoid invalid nat_net pointer use on failed nf_nat_init() [ Upstream

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

CVE: CVE-2026-72419
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: netfilter: nf_nat: avoid invalid nat_net pointer use on failed nf_nat_init() [ Upstream
Commit: 359d8ff97362a4662356104540e4814bff9dad7c
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=359d8ff97362a4662356104540e4814bff9dad7c
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72419
Analysis date: Sat, 15 Aug 2026 15:47:41 -0400
ActionableScore: 7
ActionableScore lower bound: 4
Actionable bucket: Strong Important candidate / Actionable Moderate at minimum
Manual review required: YES

Summary:
A failed built-in `nf_nat_init()` can leave `nat_net_id` stale after per-net id reuse, causing nf_nat to interpret another per-net object as `struct nat_net` and triggering a local type-confusion/OOB access through nftables NAT control operations.

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ABOUT THIS REPORT
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The original Linux kernel CVE announcement for CVE-2026-72419 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72419

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-2026-72419	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-843;CWE-125;*CWE-787;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:L/I:L/A:H';BEST CVSS score: '7';DESCR 'A failed built-in nf_nat_init() can leave nat_net_id stale after unregister_pernet_subsys releases the per-net id for reuse. Later nft_chain_nat.ko or another dependent netfilter component may still call nf_nat_register_fn, causing net_generic() to return an object of a different type such as synproxy_net instead of nat_net. This is a type confusion that produced a KASAN slab OOB access and may crash the kernel or corrupt adjacent kernel memory depending on the exact access pattern. For the CVSS the PR:L is used for the paranoid score because delegated CAP_NET_ADMIN, container root, or a restricted service account may be enough to reach the nft NAT control path in some deployments. The issue is not directly network reachable and is triggered through local netfilter control plane operations. Impact is at least local denial of service via kernel crash and in the worst case may allow confidentiality or integrity impact due to kernel type confusion and OOB access.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 6)	YES	REMOTE READ KASAN OOB INIT BPF NETFILTER LEAK HARDWARE TEST  KPANIC INCREASED_FROM_LOW_BASED_ON_REQUIREMANUALCHECK KPANIC INCREASED_TO_HIGH_BASED_ON_ACTIONABLESCOREHIGHEREQTHAN6 DECREASED_TO_MODERATE7_BASED_ON_FALSEPOSCHECKOFKP	YES	NO	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=7
ActionableScoreLower=4

## 1. ActionableScore

* Conservative score: **4**
* Paranoid score: **7**
* Final recommended bucket: **Strong Important candidate / Actionable Moderate at minimum**::

## 2. Signal breakdown

Paranoid scoring signals:

* **Generic memory corruption / type confusion: +2**
  `net_generic()` may return a different per-net object type, e.g. `struct synproxy_net` instead of `struct nat_net`, producing a documented KASAN slab OOB access.

* **Weak LPE concern: +1**
  The primitive is not an arbitrary write, but it is invalid struct interpretation in kernel networking state, with possible follow-on corruption in register/unregister paths.

* **Real lifetime corruption: +1**
  `nat_net_id` survives after `unregister_pernet_subsys()` releases the per-net id, allowing stale id reuse.

* **Reliable kernel crash / strong DoS: +1**
  The report shows a reproducible KASAN slab-out-of-bounds access from `iptables`/nf_tables NAT setup.

* **Integrity impact plausible: +1**
  The wrong per-net object may be used by NAT registration/unregistration logic, so this is more than a pure read-only bounds issue.

* **Broad/common subsystem: +1**
  Netfilter/NAT/nf_tables are widely deployed kernel networking components, although this specific failure mode is configuration dependent.

* **Common networking/netfilter control path: +1**
  The trigger path is nfnetlink/nf_tables control plane, not packet RX, but it is still a central networking configuration path.

Subtractions:

* **Rare/configuration-dependent condition: -1**
  Requires built-in `nf_nat`, failed `nf_nat_init()` during BPF kfunc registration, and later dependent NAT code still being reachable.

Conservative-only reductions:

* **Requires admin/root/CAP_NET_ADMIN in typical deployments: -2**
  Normal triggering requires nftables/iptables NAT control operations.

* **Constrained or not demonstrated arbitrary corruption: -1**
  The report shows OOB/type confusion, but not a controlled overwrite, reclaim primitive, or demonstrated LPE chain.

## 3. Reachability analysis

The bug is triggered locally through netfilter control-plane operations such as adding NAT chains via nf_tables/iptables. In typical host deployments this requires root or `CAP_NET_ADMIN`, so the conservative score is reduced. In containerized or delegated-network-admin environments, `CAP_NET_ADMIN` may be available to a reduced-privilege actor, so the paranoid score should not treat this as full host-root only.

The issue is **not directly network reachable**. Packet traffic alone is not enough. The unusual precondition is that built-in `nf_nat_init()` must fail and leave code/static state callable by dependent modules while the per-net id has been released and possibly reused.

## 4. Severity interpretation

This is not an ordinary Moderate cleanup bug. The patch prevents an explicit **type confusion** and **slab OOB access** caused by stale per-net id reuse. Realistic exploitation evidence currently supports local crash/DoS most strongly, but the object-type confusion in a core networking subsystem is sufficient for manual review and paranoid Important-candidate handling.

Theoretical LPE is not proven, because there is no demonstrated arbitrary write, controlled object replacement, or exploit chain. However, the bug class and affected register/unregister paths justify treating it as **Actionable Moderate at minimum**, with **Strong Important candidate** status for paranoid triage.

## 5. One-sentence report phrase

A failed built-in `nf_nat_init()` can leave `nat_net_id` stale after per-net id reuse, causing nf_nat to interpret another per-net object as `struct nat_net` and triggering a local type-confusion/OOB access through nftables NAT control operations.

## 6. Manual review recommendation

**MANUAL CHECK REQUIRED**

Reason: this is an explicit kernel type-confusion/OOB access in netfilter per-net state, with plausible corruption beyond simple DoS, even though the normal trigger requires privileged netfilter control access and unusual initialization-failure conditions.

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

Patch: netfilter: nf_nat: avoid invalid nat_net pointer use on failed nf_nat_init() [ Upstream
Commit: 359d8ff97362a4662356104540e4814bff9dad7c
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=359d8ff97362a4662356104540e4814bff9dad7c

Changed files:
  net/netfilter/nf_nat_core.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=359d8ff97362a4662356104540e4814bff9dad7c

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

The original Linux kernel CVE announcement for CVE-2026-72419 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72419

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:L/I:L/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: 4
  Paranoid ActionableScore: 7

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).