[CVE-2026-43341][MODERATE 7.0] net/ipv6: ioam6: prevent schema length wraparound in trace fill [ Upstream

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

CVE: CVE-2026-43341
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: net/ipv6: ioam6: prevent schema length wraparound in trace fill [ Upstream
Commit: e96d48b37708d53cbdc47f6f60b0714fc4a5f596
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=e96d48b37708d53cbdc47f6f60b0714fc4a5f596
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-43341
Analysis date: Thu, 24 Sep 2026 17:40:47 -0400
ActionableScore: 6
ActionableScore lower bound: 5
Actionable bucket: Actionable Moderate / Strong Important candidate requiring manual review
Manual review required: YES

Summary:
No one-sentence report phrase was found.

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ABOUT THIS REPORT
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The original Linux kernel CVE announcement for CVE-2026-43341 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-43341

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-2026-43341	MODERATE	https://www.kernelcve.org/list/?q=CVE-2026-43341 CHECK WITH IMPACT FROM ORIG NN IMPORTANT	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H';CWE-190;*CWE-787;CWE-122;Other CVSS 'AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H';BEST CVSS score: '9.8';DESCR 'An integer wraparound in ioam6_fill_trace_data can occur because the schema trace length is stored in a u8 value. A schema with bit 22 enabled and the maximum payload makes the calculated length wrap from 256 to 0, bypassing the remaining trace buffer space check. The subsequent trace fill writes the schema header and payload beyond the allocated trace area in an skb. A remote IPv6 sender may reach this path when IOAM6 processing is enabled and a matching large schema is configured on the target. For the CVSS the PR:N because a remote sender does not need an account or local privileges on the target after the vulnerable IOAM6 configuration is deployed. The base score uses AC:H because the required IOAM6 namespace and large schema configuration are specialized conditions outside the attacker control. Impact may include kernel crash and memory corruption. Confidentiality integrity and availability impact are rated High for the paranoid score because the patch demonstrates an out of bounds kernel write. This is not normally exposed to the public Internet because IOAM6 is generally used in controlled IPv6 network domains.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate / Strong Important candidate requiring manual review (with actual score 6)	MAYBE	REMOTE SIMPLEFIX NETWORK LINUS IPV6 KPANIC  DECREASED_TO_MODERATE7_BASED_ON_FALSEPOSCHECKOFDH	-	-	checked

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

ActionableScore=6
ActionableScoreLower=5
PrimitiveClass=CLASS_B
RealUAF=NO
HostAdminRequired=NO
NamespaceScopedPrivilege=UNKNOWN
ImportantCandidate=YES
ManualReview=REQUIRED
AutoDowngradeAllowed=NO

1. ActionableScore

* Raw conservative score: 3
* Conservative score: 5
* Raw paranoid score: 4
* Paranoid score: 6
* Applied conservative manual-review safety floor: 3 -> 5. A concrete kernel out-of-bounds write of up to approximately 1024 bytes remains unresolved beyond a simple invalid read or WARN.
* Applied paranoid manual-review safety floor: 4 -> 6. The stronger interpretation remains within the demonstrated overwrite class and does not assume arbitrary kernel write or privilege escalation.
* Final recommended bucket: **Actionable Moderate / Strong Important candidate requiring manual review**::

2. Signal breakdown

Positive signals:

* +1 Constrained kernel buffer overwrite. The schema length wraps from 256 to 0, bypasses the remaining-space validation, and causes the schema header and full schema payload to be copied beyond the intended IOAM trace area in an skb.
* +1 Realistic kernel crash or strong DoS. A write beyond an skb trace buffer can corrupt adjacent skb or kernel memory and can realistically lead to an Oops, panic, or network-stack instability.
* +1 Remote packet reachability under enabled IOAM6 processing. A remote IPv6 sender can provide the IOAM trace packet that reaches the vulnerable fill path once the target is deployed with a matching IOAM6 namespace and schema.
* +1 Paranoid only. The vulnerable destination is an skb associated with attacker-supplied network traffic. The attacker does not control an arbitrary kernel address, but the write occurs in packet-processing memory and the exact overwrite position depends on attacker-provided packet layout and trace-space conditions.

Negative or non-awarded signals:

* No controlled reclaim, object substitution, callback control, arbitrary kernel write, or directed target selection is demonstrated.
* No privilege escalation, confidentiality disclosure, integrity compromise of a protected object, or public exploit is supplied.
* No UAF, double free, refcount mutation, or stale lifetime operation is present.
* No additional Availability point is awarded. The likely crash or DoS effect is counted only once.
* No common networking core-path bonus is awarded. IOAM6 is IPv6 networking functionality, but this specific IOAM trace schema path is not established as broadly deployed or normally exercised.
* No niche-subsystem penalty is applied. The supplied evidence does not establish that IOAM6 is unreachable by an attacker once a target operator has enabled it.
* No hard-race penalty is applied. This is deterministic integer truncation and bounds-check bypass, not a timing race.

3. Reachability analysis

The immediate trigger is a specially formed IPv6 IOAM trace packet processed by the target. The remote sender does not need a local account, CAP_NET_ADMIN, or host administrator privileges after the target has deployed the relevant IOAM6 configuration. Therefore, HostAdminRequired is NO for the packet sender threat model.

The vulnerable path depends on IOAM6 being enabled and on a matching namespace and schema being configured with bit 22 and the maximum schema payload. Such configuration is likely performed through the IOAM Generic Netlink control plane and normally requires administrative control when it is created. However, this is a target deployment prerequisite rather than a privilege the remote attacker must possess to send the triggering packet.

NamespaceScopedPrivilege is UNKNOWN. The supplied patch does not show the Generic Netlink capability checks, the namespace ownership model for IOAM6 namespaces and schemas, or whether an attacker can create every required configuration element in an attacker-controlled network namespace. The remote packet path itself is independent of local namespace privileges once the vulnerable configuration exists.

No special hardware, firmware interaction, race timing, or physical access is required by the demonstrated arithmetic failure.

4. Primitive and severity interpretation

The exact primitive is a concrete integer-wraparound-driven out-of-bounds write. The u8 variable sclen stores a calculated encoded schema length. With schema bit 22 enabled and a 1020-byte payload, the encoded length becomes 256 and wraps to zero. The zero value bypasses the remaining-space check, while the later fill operation still copies the full schema header and payload.

This is not a UAF and does not involve a stale object or destructor path. It is an overwrite of memory associated with an skb trace buffer. The patch directly establishes a buffer overrun, but does not establish attacker-controlled overwrite bytes, arbitrary target selection, controlled replacement of kernel objects, callback invocation, or a post-corruption privilege-escalation primitive.

The write is materially more serious than an invalid dereference or a validation-only failure because it can overwrite beyond the intended kernel packet buffer region. However, the supplied evidence does not prove that the attacker can select the adjacent kernel object, preserve execution after corruption, read corrupted memory back, or obtain arbitrary kernel read or write capability.

PrimitiveClass is CLASS_B. The patch establishes real kernel memory corruption, but the corruption remains constrained because the copied schema contents are generated according to the configured IOAM schema and the destination is adjacent to the trace area in an skb rather than an attacker-selected kernel address.

ImportantCandidate is YES because a concrete network-reachable kernel out-of-bounds write exists and its practical exploitation leverage requires analysis of the complete IOAM6 trace-building path, skb allocation layout, schema payload generation, and deployment configuration. AutoDowngradeAllowed is NO because automatically treating this as an ordinary crash-only issue would discard an established kernel overwrite primitive.

Likely operational severity is at least remote denial of service for enabled IOAM6 deployments. The possibility of confidentiality, integrity, or privilege impact is unresolved rather than demonstrated. The paranoid score preserves this unresolved kernel-memory-corruption concern without claiming arbitrary write or proven escalation.

5. One-sentence report phrase

An integer wraparound in IOAM6 trace schema length calculation can bypass skb trace-buffer bounds validation and cause a remote IPv6 packet to write a schema header and payload beyond the intended kernel buffer when a matching IOAM6 schema is configured.

6. Manual review recommendation

MANUAL CHECK REQUIRED

A concrete kernel out-of-bounds write is established. Review the IOAM6 configuration and namespace setup path, the exact schema payload sources, skb allocation and expansion behavior, and whether external IPv6 peers can reach IOAM6 trace processing.

7. Call-site confidence

Call-site confidence: medium

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

Patch: net/ipv6: ioam6: prevent schema length wraparound in trace fill [ Upstream
Commit: e96d48b37708d53cbdc47f6f60b0714fc4a5f596
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=e96d48b37708d53cbdc47f6f60b0714fc4a5f596

Changed files:
  net/ipv6/ioam6.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=e96d48b37708d53cbdc47f6f60b0714fc4a5f596

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

The original Linux kernel CVE announcement for CVE-2026-43341 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-43341

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:H/I:H/A:H
  The Best / paranoid CVSS vector: AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
  The Best / paranoid CVSS score: 9.8

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).