[CVE-2026-45847][LOW] net: remove WARN_ON_ONCE when accessing forward path array [ Upstream

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

CVE: CVE-2026-45847
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: net: remove WARN_ON_ONCE when accessing forward path array [ Upstream
Commit: 548244c2f542aa0ad49453e9306e715a3877bc44
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=548244c2f542aa0ad49453e9306e715a3877bc44
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-45847
Analysis date: Thu, 28 May 2026 01:04:56 -0400
ActionableScore: 1
ActionableScore lower bound: unknown
Actionable bucket: Ordinary Moderate / Low-like
Manual review required: NO

Summary:
A sufficiently long locally configured forwarding path could trigger a `WARN_ON_ONCE` in `dev_fwd_path()`, but the bounds check still returned `NULL`, limiting impact to warning-driven availability effects such as `panic_on_warn`.

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

The original Linux kernel CVE announcement for CVE-2026-45847 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-45847

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: LOW
Manual review required: NO

A detailed explanation of the methodology and priority rules is included
at the end of this message.

======================================================================
AL-KERNEL CLASSIFICATION RESULT
======================================================================

CVE-2026-45847	LOW	CHECK	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:L';CWE-617;CWE-703;CWE-755;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '2.5';DESCR 'dev_fwd_path could hit a reachable WARN_ON_ONCE when userspace constructs a forwarding path longer than NET_DEVICE_PATH_STACK_MAX, especially with IPIP tunnel stacking. The bounds check still returns NULL, so the patch context does not show an out-of-bounds access or memory corruption primitive. For the CVSS the PR:L is used for the paranoid score only when reduced privilege users have delegated CAP_NET_ADMIN or network namespace control to create long virtual device paths. The issue is not directly network reachable and requires local control plane configuration. Impact is limited to a kernel warning or possible availability impact on systems configured to panic on warnings.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate / Low-like (with actual score 1) 	MAYBE	REMOTE SIMPLEFIX  DECREASED_TO_MODERATE_REGULAR_FROM_MODERATE7_BASED_ON_GUESSCVSS DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_ACTIONABLESCORELESSTHAN3	-	-	checked

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

ActionableScore=1

## 1. ActionableScore

* Conservative score: 1
* Paranoid score: 1
* Final recommended bucket: **Ordinary Moderate / Low-like**::

## 2. Signal breakdown

Triggered signals:

* Availability impact realistic: +1. The only supported impact is a reachable `WARN_ON_ONCE`, which may matter on systems configured with `panic_on_warn`.

Subtracting / limiting factors:

* Requires admin/root/CAP_NET_ADMIN in typical deployments: -2. Building long virtual forwarding paths or IPIP tunnel stacks normally requires network administration privileges.
* No remote reachable signal. Packet traffic alone does not create the forwarding path.
* No memory corruption. The bounds check still returns `NULL` and does not access `stack->path[k]` when `k >= NET_DEVICE_PATH_STACK_MAX`.
* No confidentiality or integrity impact.
* No privilege escalation primitive.

I keep the effective score at 1 rather than negative because reachable kernel warnings can still have operational availability relevance under `panic_on_warn`.

## 3. Reachability analysis

The bug is reachable only through local network control-plane configuration that builds a sufficiently long forwarding path, more likely with IPIP tunnel stacking. In normal deployments this requires `CAP_NET_ADMIN` or equivalent administrative control.

Namespaces and containers can lower practical access if a container is granted network namespace control or delegated `CAP_NET_ADMIN`, but the result is still only a warning path with a safe `NULL` return. The path is not default-triggerable by ordinary remote packets.

## 4. Severity interpretation

This behaves like Low / ordinary Moderate at most. It is a warning-removal patch, not a memory safety fix. The realistic impact is warning noise or a panic only on hardened/debug systems configured to panic on warnings.

There is no theoretical memory corruption supported by the diff because the array bounds check remains in place.

## 5. One-sentence report phrase

A sufficiently long locally configured forwarding path could trigger a `WARN_ON_ONCE` in `dev_fwd_path()`, but the bounds check still returned `NULL`, limiting impact to warning-driven availability effects such as `panic_on_warn`.

## 6. Manual review recommendation

NO MANUAL CHECK NEEDED

This can be auto-closed for security triage unless the deployment treats `panic_on_warn` as a critical availability exposure. No memory corruption, information leak, privilege escalation, or network-triggered attack path is supported.

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

Patch: net: remove WARN_ON_ONCE when accessing forward path array [ Upstream
Commit: 548244c2f542aa0ad49453e9306e715a3877bc44
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=548244c2f542aa0ad49453e9306e715a3877bc44

Changed files:
  net/core/dev.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=548244c2f542aa0ad49453e9306e715a3877bc44

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

The original Linux kernel CVE announcement for CVE-2026-45847 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-45847

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:N/I:N/A:L
  The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:L
  The Best / paranoid CVSS score: 2.5

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: unknown
  Paranoid ActionableScore: 1

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: LOW
KPANIC detected for this report: NO
Published priority for this report (same as in Subject): LOW

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).