[CVE-2026-46037][MODERATE 7.0] ipv4: icmp: validate reply type before using icmp_pointers

[CVE-2026-46037][MODERATE 7.0] ipv4: icmp: validate reply type before using icmp_pointers

[AL-KERNEL]

CVE: CVE-2026-46037
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: ipv4: icmp: validate reply type before using icmp_pointers
Commit: 92e7c209036dcc0e8ffdf806fdfd3645b263bea5
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=92e7c209036dcc0e8ffdf806fdfd3645b263bea5
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-46037
Analysis date: Wed, 27 May 2026 10:03:39 -0400
ActionableScore: 5
ActionableScore lower bound: 3
Actionable bucket: Actionable Moderate at minimum
Manual review required: YES

Summary:
A remotely reachable IPv4 ICMP Extended Echo reply path can index `icmp_pointers[]` out of bounds, causing a constrained kernel OOB read with likely DoS impact and requiring manual review due to network exposure.

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

The original Linux kernel CVE announcement for CVE-2026-46037 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-46037

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.

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

CVE-2026-46037	MODERATE	CHECK	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-129;*CWE-20;Other CVSS 'AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '7';DESCR 'An out of bounds read can occur in the IPv4 ICMP reply path because ICMP_EXT_ECHOREPLY may be used as an index into icmp_pointers even though that type is outside the traditional ICMP type range covered by the array. A remote host may reach this path by causing an RFC 8335 Extended Echo reply if the target is configured to answer such PROBE traffic and filtering allows it. For the CVSS the PR:N is used because no local privileges are needed once the ICMP PROBE reply path is reachable over the network. AC:H is used because practical triggering depends on Extended Echo response configuration and network policy. Impact is primarily denial of service or invalid kernel memory read behavior. In the worst still defensible case the out of bounds read may cause limited confidentiality or integrity concern through wrong metadata interpretation, but the patch does not support an out of bounds write, UAF, or privilege escalation primitive.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate at minimum (with actual score 4)	YES	REMOTE SIMPLEFIX NETWORK LINUS  DECREASED_TO_MODERATE70_BASED_ON_ACTIONABLESCORELOWERTHAN7 DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5	NO	NO	checked

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

ActionableScore=5
ActionableScoreLower=3

## 1. ActionableScore

* Conservative score: 3
* Paranoid score: 5
* Final recommended bucket: **Actionable Moderate at minimum**::

## 2. Signal breakdown

Conservative signals:

* Remote reachable / network-triggerable: +2
  The affected path is in IPv4 ICMP reply generation and may be reachable by remote ICMP Extended Echo PROBE traffic if the target responds to RFC 8335 probes.

* Common networking core path: +1
  This is IPv4 ICMP handling, not a niche local-only driver path.

* Weak corruption: +0
  The primitive is an out-of-bounds read from `icmp_pointers[]`, not an OOB write, UAF, double free, or controlled overwrite.

* Corruption primitive highly constrained or read-only: -1
  The observed access is a small read of the `.error` field from an out-of-range array entry, with no attacker-controlled payload or write target.

* Availability impact plausible: +1
  Invalid kernel memory reads in a network path may cause warnings, KASAN findings, incorrect behavior, or crash depending on layout and build.

Paranoid additional signals:

* Broad/default/common subsystem exposure: +1
  IPv4 ICMP is broadly deployed, even though this specific Extended Echo path may depend on configuration and filtering.

* Confidentiality or integrity concern weakly plausible: +1
  The OOB read may influence metadata interpretation such as whether `nf_ct_attach()` is called, but there is no demonstrated disclosure path or write primitive.

## 3. Reachability analysis

A remote host may trigger the vulnerable path by causing the kernel to generate an RFC 8335 Extended Echo Reply using `ICMP_EXT_ECHOREPLY`, which is outside the valid range for `icmp_pointers[]`. This requires the target to support and answer Extended Echo PROBE traffic and for ICMP filtering or policy not to block it.

No local account is required once the network path is reachable. Namespaces and containers are not central to triggering this issue, although containerized networking policy may affect whether such packets reach the host stack. This is not ordinary local netlink or ioctl control-plane exposure.

## 4. Severity interpretation

This is best treated as Actionable Moderate rather than Important. The bug is network reachable in a core IPv4 ICMP path, which makes it unsuitable for automatic low-priority closure.

However, the actual primitive shown by the patch is a constrained OOB read used as a boolean metadata check. There is no evidence of OOB write, UAF, arbitrary write, object lifetime corruption, or a practical LPE path. Realistic impact is most likely DoS or incorrect conntrack attachment behavior, while broader C/I impact remains speculative.

## 5. One-sentence report phrase

A remotely reachable IPv4 ICMP Extended Echo reply path can index `icmp_pointers[]` out of bounds, causing a constrained kernel OOB read with likely DoS impact and requiring manual review due to network exposure.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

Reason: this is a network-reachable OOB read candidate in a core IPv4 ICMP path. It is not clearly Important based on the patch alone, but it should not be auto-closed because reachability and adjacent-memory effects need confirmation.

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

Patch: ipv4: icmp: validate reply type before using icmp_pointers
Commit: 92e7c209036dcc0e8ffdf806fdfd3645b263bea5
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=92e7c209036dcc0e8ffdf806fdfd3645b263bea5

Commit description:

Extended echo replies use ICMP_EXT_ECHOREPLY as the outbound reply type.
That value is outside the range covered by icmp_pointers[], which only
describes the traditional ICMP types up to NR_ICMP_TYPES.

Avoid consulting icmp_pointers[] for reply types outside that range, and
use array_index_nospec() for the remaining in-range lookup. Normal ICMP
replies keep their existing behavior unchanged.

Fixes: d329ea5 ("icmp: add response to RFC 8335 PROBE messages")
Cc: stable@kernel.org
Reported-by: Yuan Tan <yuantan098@gmail.com>
Reported-by: Yifan Wu <yifanwucs@gmail.com>
Reported-by: Juefei Pu <tomapufckgml@gmail.com>
Reported-by: Xin Liu <bird@lzu.edu.cn>
Signed-off-by: Ruide Cao <caoruide123@gmail.com>
Signed-off-by: Ren Wei <n05ec@lzu.edu.cn>
Reviewed-by: Simon Horman <horms@kernel.org>
Link: https://patch.msgid.link/0dace90c01a5978e829ca741ef684dbd7304ce62.1776628519.git.caoruide123@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  net/ipv4/icmp.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=92e7c209036dcc0e8ffdf806fdfd3645b263bea5

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

The original Linux kernel CVE announcement for CVE-2026-46037 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-46037

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: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: 3
  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).