[CVE-2026-72442][MODERATE 7.0] netfilter: flowtable: fix and simplify IP6IP6 tunnel handling [ Upstream

[CVE-2026-72442][MODERATE 7.0] netfilter: flowtable: fix and simplify IP6IP6 tunnel handling [ Upstream

[AL-KERNEL]

CVE: CVE-2026-72442
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: netfilter: flowtable: fix and simplify IP6IP6 tunnel handling [ Upstream
Commit: 7f8d816a9aa2729d270418f00c9ef5e85bfc1b31
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=7f8d816a9aa2729d270418f00c9ef5e85bfc1b31
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72442
Analysis date: Sun, 16 Aug 2026 00:17:35 -0400
ActionableScore: 6
ActionableScore lower bound: 5
Actionable bucket: Actionable Moderate at minimum
Manual review required: YES

Summary:
An IP6IP6 netfilter flowtable fast-path bug failed to ensure the outer IPv6 header was linear in skb headroom before later packet processing, allowing remote traffic through a configured IPv6 tunnel flowtable path to potentially trigger a kernel crash or forwarding DoS.

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

The original Linux kernel CVE announcement for CVE-2026-72442 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72442

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-2026-72442	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:L/I:L/A:H';CWE-125;*CWE-20;CWE-754;Other CVSS 'AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '7';DESCR 'IP6IP6 handling in the netfilter flowtable fast path could examine an outer IPv6 header through skb_header_pointer without ensuring that the header was pulled into the linear skb head area required by later processing. A remote packet can potentially reach this path when nft flowtable acceleration and IP6IP6 tunnel offload are configured, especially in router or internal network deployments using IPv6 tunnels. For the CVSS the PR:N is used because the attacker does not need a local account on the victim and only needs packet reachability to the affected forwarding path. AC:H is used because reliable triggering depends on a specific nft flowtable and IP6IP6 tunnel configuration and on packet layout conditions. Impact is primarily denial of service through packet processing fault or kernel crash. For the paranoid score, limited confidentiality or integrity impact is kept possible due to a network reachable skb memory handling bug, but there is no strong evidence for an arbitrary write or stable privilege escalation primitive.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate at minimum (with actual score 7)  SKIP CVE-2026-72442 UNKNOWN SKIP The Fixes patch not applied yet, so unlikely that actual: d98103575dcdd3a730e0901ab457791a9ac6930c YES  NO NO unknown 	MAYBE	REMOTE DANGER NETWORK SKB IPV6 KPANIC PACKET  KPANIC INCREASED_TO_HIGH_BASED_ON_ACTIONABLESCOREHIGHEREQTHAN6 DECREASED_TO_MODERATE7_BASED_ON_FALSEPOSCHECKOFDH	-	-	checked

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

ActionableScore=6
ActionableScoreLower=5

## 1. ActionableScore

* Conservative score: 5
* Paranoid score: 6
* Final recommended bucket: **Actionable Moderate at minimum**::

## 2. Signal breakdown

Triggered signals:

* Remote reachable / network-triggerable: +2
  A forwarded IPv6 packet can reach the netfilter flowtable fast path when nft flowtable acceleration and IP6IP6 tunnel handling are configured.

* Memory layout invariant restoration: +1
  The patch replaces skb_header_pointer() with pskb_may_pull() to ensure the outer IPv6 header is actually linear in skb headroom before later direct skb header access.

* Reliable kernel crash / strong DoS concern: +1
  The bug can lead to invalid packet processing state and likely kernel fault or packet-processing failure in the forwarding path.

* Common networking core path or packet-processing path: +1
  The affected code is in netfilter flowtable packet forwarding logic.

Paranoid-only additional signal:

* Memory corruption, weak/indirect corruption candidate: +1
  This is not an OOB write or UAF, but it is an skb header linearization bug where later code may access packet data assuming a layout invariant that was not enforced.

Not awarded:

* No strong generic memory corruption +2
  The patch does not show UAF, double free, OOB write, arbitrary write, type confusion, or attacker-controlled overwrite.

* No privilege escalation plausible +2
  There is no demonstrated reclaim, write primitive, callback control, or object confusion.

* No C/I impact in conservative score
  Limited C/I concern is too speculative for the main score.

## 3. Reachability analysis

A remote sender may trigger the affected path by sending traffic through a system acting as a router or forwarding node with nft flowtable acceleration and IP6IP6 tunnel offload enabled. No local account on the victim is needed for the packet trigger itself, so PR:N is reasonable for CVSS-style reachability once the vulnerable forwarding path is exposed.

The configuration is not universal default desktop/server exposure. It requires netfilter flowtable plus IPv6 tunnel acceleration, likely in router, gateway, or internal network deployments. Namespaces mainly matter for configuring the vulnerable setup, which requires administrative network privileges, but the attacker who sends packets through an already configured forwarding path does not need those privileges.

## 4. Severity interpretation

This behaves like an actionable Moderate issue, with Important-candidate scrutiny justified only in paranoid triage because it is network reachable packet parsing in an skb fast path.

The realistic demonstrated impact is DoS or packet-processing fault. The theoretical concern is that an skb layout invariant violation in a central packet path can sometimes hide stronger memory access consequences, but the patch does not support treating this as strong memory corruption or LPE.

## 5. One-sentence report phrase

An IP6IP6 netfilter flowtable fast-path bug failed to ensure the outer IPv6 header was linear in skb headroom before later packet processing, allowing remote traffic through a configured IPv6 tunnel flowtable path to potentially trigger a kernel crash or forwarding DoS.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

Reason: network-reachable packet-processing path plus skb header linearization bug. Even though the demonstrated impact is mainly DoS, this should not be auto-closed without manual review.

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

Patch: netfilter: flowtable: fix and simplify IP6IP6 tunnel handling [ Upstream
Commit: 7f8d816a9aa2729d270418f00c9ef5e85bfc1b31
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=7f8d816a9aa2729d270418f00c9ef5e85bfc1b31

Changed files:
  net/ipv6/ip6_tunnel.c
  net/netfilter/nf_flow_table_ip.c
  tools/testing/selftests/net/netfilter/nft_flowtable.sh

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=7f8d816a9aa2729d270418f00c9ef5e85bfc1b31

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

The original Linux kernel CVE announcement for CVE-2026-72442 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72442

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:H
  The Best / paranoid CVSS vector: AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/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: 5
  Paranoid ActionableScore: 6

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).