[CVE-2026-63870][MODERATE REGULAR] ieee802154: 6lowpan: only accept IPv6 packets in lowpan_xmit() [ Upstream

[CVE-2026-63870][MODERATE REGULAR] ieee802154: 6lowpan: only accept IPv6 packets in lowpan_xmit() [ Upstream

[AL-KERNEL]

CVE: CVE-2026-63870
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: ieee802154: 6lowpan: only accept IPv6 packets in lowpan_xmit() [ Upstream
Commit: af07fffbd53ddc3ec3c2a4ca914f27899fa89bca
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=af07fffbd53ddc3ec3c2a4ca914f27899fa89bca
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-63870
Analysis date: Sun, 19 Jul 2026 11:02:33 -0400
ActionableScore: 4
ActionableScore lower bound: 2
Actionable bucket: Borderline Moderate / manual review recommended
Manual review required: YES

Summary:
A non IPv6 skb queued to an ieee802154 6LoWPAN interface can cause `lowpan_xmit()` to use uninitialized `lowpan_addr_info`, potentially leading to malformed transmission behavior or limited kernel data disclosure, but exploitation appears local or configuration dependent rather than directly remote.

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

The original Linux kernel CVE announcement for CVE-2026-63870 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-63870

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 REGULAR
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-2026-63870	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:L/I:L/A:H';*CWE-457;CWE-908;*CWE-200;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:N/A:L';BEST CVSS score: '5.8';DESCR 'The 6LoWPAN transmit path can use uninitialized lowpan_addr_info when a non IPv6 skb is queued to a 6LoWPAN interface. The header creation path may return without initializing this metadata, while lowpan_xmit() later treats it as valid input for header construction. This is primarily a local or locally configured network stack issue rather than a directly remote packet processing flaw. For the CVSS the PR:L is used because triggering requires a local process or delegated capability able to inject or route a non IPv6 packet through the 6LoWPAN transmit path. Impact is at least a local denial of service or malformed transmit behavior, with possible limited confidentiality impact if uninitialized kernel data is copied into an outgoing frame. The paranoid score keeps the same bug class and raises impact only to the highest still defensible interpretation for manual review sensitivity.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline Moderate / manual review recommended (with actual score 3)	YES	INIT SIMPLEFIX SKB LINUS TEST IPV6 SYZBOT PACKET  INCREASED_FROM_LOW_BASED_ON_REQUIREMANUALCHECK DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5	NO	NO	checked

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

ActionableScore=4
ActionableScoreLower=2

## 1. ActionableScore

* Conservative score: 2
* Paranoid score: 4
* Final recommended bucket: **Borderline Moderate / manual review recommended**::

## 2. Signal breakdown

Conservative signals:
* Local trigger: +1. A local process or locally configured test path can queue a non IPv6 skb through a 6LoWPAN interface.
* Weak indirect corruption candidate: +1. The bug uses uninitialized `lowpan_addr_info` as transmit metadata, but the patch does not show UAF, OOB write, arbitrary write, or controlled object replacement.
* Confidentiality impact plausible: +1. Uninitialized kernel metadata may influence or be copied into an outgoing frame.
* Rare and difficult to reach subsystem/configuration: -1. 6LoWPAN over ieee802154 is not a broad default path and triggering needs unusual interface setup.

Paranoid additional signals:
* Integrity impact plausible: +1. Uninitialized address metadata may affect header construction or packet destination semantics.
* Availability impact plausible: +1. Malformed transmit behavior or driver/network stack errors are possible, but no reliable crash primitive is shown.
* Same rare configuration penalty remains: -1.

No strong memory corruption, no Dirty Pipe like primitive, no demonstrated LPE path, and no direct remote reachability are supported by the patch.

## 3. Reachability analysis

The realistic trigger is local or locally configured: a non IPv6 packet must be queued for transmission on a 6LoWPAN interface. This likely requires either local packet injection plus an existing misconfigured 6LoWPAN device, or administrative/delegated network setup such as CAP_NET_ADMIN in a namespace. It is not a normal remote receive path and should not be scored as directly network reachable. Namespace setups may reduce practical privileges if untrusted users can create or control the relevant netdev topology, but typical production exposure is limited.

Call-site confidence: medium. The commit explains the relevant call path from header creation to `lowpan_xmit()`, but the full caller graph is not present in the provided diff.

## 4. Severity interpretation

This behaves more like a borderline Moderate issue than an Important-class vulnerability. The strongest supported primitive is use of uninitialized kernel data in a network transmit metadata path. Theoretical confidentiality or malformed packet effects are plausible, but there is no evidence of attacker-controlled memory corruption, privilege escalation, arbitrary write, UAF reclaim, or a reliable host crash. Manual review is still useful because uninitialized kernel data can sometimes become an information disclosure depending on the exact transmitted header contents.

## 5. One-sentence report phrase

A non IPv6 skb queued to an ieee802154 6LoWPAN interface can cause `lowpan_xmit()` to use uninitialized `lowpan_addr_info`, potentially leading to malformed transmission behavior or limited kernel data disclosure, but exploitation appears local or configuration dependent rather than directly remote.

## 6. Manual review recommendation

MANUAL CHECK RECOMMENDED

Reason: the issue is not strong enough for Important by itself, but uninitialized kernel data is used in a network transmit path, so the possible information disclosure surface should be manually checked before auto-closing.

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

Patch: ieee802154: 6lowpan: only accept IPv6 packets in lowpan_xmit() [ Upstream
Commit: af07fffbd53ddc3ec3c2a4ca914f27899fa89bca
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=af07fffbd53ddc3ec3c2a4ca914f27899fa89bca

Changed files:
  net/bluetooth/6lowpan.c
  net/ieee802154/6lowpan/tx.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=af07fffbd53ddc3ec3c2a4ca914f27899fa89bca

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

The original Linux kernel CVE announcement for CVE-2026-63870 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-63870

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:L/UI:N/S:U/C:L/I:N/A:L
  The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:H
  The Best / paranoid CVSS score: 5.8

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: 2
  Paranoid ActionableScore: 4

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 REGULAR

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).