[CVE-2026-63831][IMPORTANT] mac802154: llsec: add skb_cow_data() before in-place crypto

[CVE-2026-63831][IMPORTANT] mac802154: llsec: add skb_cow_data() before in-place crypto

[AL-KERNEL]

CVE: CVE-2026-63831
Priority: IMPORTANT
AL-KERNEL base severity: IMPORTANT
KPANIC flag: YES
Patch: mac802154: llsec: add skb_cow_data() before in-place crypto
Commit: 3a2b378b3a9ca75d3518d879148d2ad25b5714a9
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=3a2b378b3a9ca75d3518d879148d2ad25b5714a9
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-63831
Analysis date: Sun, 19 Jul 2026 10:19:20 -0400
ActionableScore: 8
ActionableScore lower bound: 5
Actionable bucket: Strong Important candidate / Actionable Moderate at minimum
Manual review required: YES

Summary:
mac802154 LLSEC performs in-place crypto on skb data that may be shared with other clones, allowing adjacent 802.15.4 traffic to cause shared skb corruption and possible use-after-free leading to kernel crash or worse memory-corruption impact.

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

The original Linux kernel CVE announcement for CVE-2026-63831 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-63831

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: IMPORTANT
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-2026-63831	IMPORTANT	CHECK WITH IMPACT FROM ORIG NN MODERATE	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:A/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H';*CWE-416;CWE-362;*CWE-664;*CWE-787;Other CVSS 'AV:A/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:H';BEST CVSS score: '7.5';DESCR 'mac802154 LLSEC can perform in-place crypto on skb data that is still shared with other skb clones. On the RX path a received 802.15.4 frame may be cloned before it is passed to multiple subscribers, and later LLSEC decrypt may modify the shared buffer through the crypto scatterlist. This can silently corrupt data visible to other clones and in the worst case can become a use-after-free when another clone releases the shared backing storage while crypto still writes through it. For the CVSS the PR:N is used for the paranoid score because an attacker does not need a local account if they can inject or influence reachable 802.15.4 traffic in the adjacent WPAN environment. The issue is adjacent-network reachable rather than Internet remote. Impact is at least denial of service via kernel crash and data corruption, with a defensible worst case of confidentiality and integrity impact because the bug class includes shared skb memory corruption and UAF reports.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 7)	YES	DANGER UAF SKB KERNEL_PANIC_PLUS_UAF IPV6 KPANIC  KPANIC INCREASED_TO_HIGH_BASED_ON_GUESSCVSS	NO	NO	checked

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

ActionableScore=8
ActionableScoreLower=5

## 1. ActionableScore

* Conservative score: 5
* Paranoid score: 8
* Final recommended bucket: **Strong Important candidate / Actionable Moderate at minimum**::

## 2. Signal breakdown

Triggered signals:

* Remote reachable / network-triggerable: +2
  The vulnerable path is reachable through IEEE 802.15.4 traffic when mac802154 LLSEC is enabled. This is adjacent-network reachable, not Internet remote.

* Generic memory corruption, strong corruption primitive: +2
  The commit explicitly describes shared skb data corruption and slab-use-after-free reports.

* Real lifetime corruption: +1
  The bug can involve writes through skb data that may already have been freed by another clone.

* Reliable kernel crash / strong DoS: +1
  KASAN/KMSAN slab-use-after-free and kernel crashes are explicitly mentioned.

* Weak LPE concern: +1, paranoid only
  UAF with kernel writes into freed/shared skb backing storage is a plausible escalation concern, but no controlled reclaim or exploit primitive is demonstrated.

* Dirty-Pipe-like shared ownership/COW concern: +1, paranoid only
  The root issue is missing copy-on-write isolation before in-place writes to data shared by skb clones. This is not page-cache corruption, so it should not receive the full Dirty-Pipe-like +2 treatment.

* Confidentiality impact plausible: +1, paranoid only
  Possible only as a consequence of kernel memory corruption. Not demonstrated.

* Integrity impact plausible: +1
  Silent corruption of data visible to other skb clones is directly described.

Subtracted signals:

* Hard or unreliable race / special timing required: -1
  The strongest UAF scenario depends on concurrent clone lifetime and freeing behavior.

* Rare AND difficult-to-reach subsystem/configuration: -1
  Requires IEEE 802.15.4 with LLSEC/security enabled, which is not a broad default networking path.

## 3. Reachability analysis

An attacker does not need a local account if they can inject or influence reachable IEEE 802.15.4 traffic in the adjacent WPAN environment. This supports PR:N in a CVSS-style paranoid interpretation, but the exposure is adjacent-network rather than general Internet remote.

The vulnerable path depends on mac802154 LLSEC being configured and active. This is not a common default server exposure, but it is realistic for systems using 802.15.4 security. Namespaces are not the main factor here because the primary trigger can be external radio traffic rather than a local userspace API.

Call-site confidence: high. The patch shows the exact encrypt and decrypt call sites and places skb_cow_data() immediately before in-place crypto.

## 4. Severity interpretation

This is not an ordinary Moderate cleanup. The patch addresses an skb ownership and lifetime violation where in-place crypto can modify shared data and can lead to use-after-free. Realistic impact includes adjacent-network DoS and data corruption under specific LLSEC traffic conditions.

The conservative score treats this as Actionable Moderate because the subsystem is niche and the strongest UAF condition has timing/configuration requirements. The paranoid score reaches Strong Important candidate because the patch context explicitly identifies kernel UAF and shared skb memory corruption, which should not be auto-closed without manual review.

## 5. One-sentence report phrase

mac802154 LLSEC performs in-place crypto on skb data that may be shared with other clones, allowing adjacent 802.15.4 traffic to cause shared skb corruption and possible use-after-free leading to kernel crash or worse memory-corruption impact.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

Reason: the patch explicitly fixes shared skb memory corruption and reported slab-use-after-free, and the trigger can be adjacent-network reachable in affected 802.15.4 LLSEC deployments.

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

Patch: mac802154: llsec: add skb_cow_data() before in-place crypto
Commit: 3a2b378b3a9ca75d3518d879148d2ad25b5714a9
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=3a2b378b3a9ca75d3518d879148d2ad25b5714a9

Commit description:

llsec_do_encrypt_unauth(), llsec_do_encrypt_auth(),
llsec_do_decrypt_unauth(), and llsec_do_decrypt_auth() all perform
in-place cryptographic transformations on skb data.  They build a
scatterlist with sg_init_one() pointing into the skb's linear data area
and then pass the same scatterlist as both src and dst to the crypto API
(e.g. crypto_skcipher_encrypt/decrypt, crypto_aead_encrypt/decrypt).

On the RX path, __ieee802154_rx_handle_packet() clones the received skb
before handing it to each subscriber via ieee802154_subif_frame().  The
cloned skb shares the same underlying data buffer via reference
counting.  When llsec_do_decrypt() subsequently modifies this shared
buffer in place, it corrupts data that other clones -- potentially
belonging to other sockets or subsystems -- still reference.

On the TX path, similar data sharing can occur when an skb's head has
been cloned (skb_cloned() returns true).

The fix is to call skb_cow_data() before performing any in-place crypto
operation.  skb_cow_data() ensures that the skb's data area is not
shared: if the skb head is cloned or the data spans multiple fragments,
it copies the data into a private buffer that can be safely modified in
place.  This is the same pattern used by:

  - ESP (net/ipv4/esp4.c, net/ipv6/esp6.c)
  - MACsec (drivers/net/macsec.c)
  - WireGuard (drivers/net/wireguard/receive.c)
  - TIPC (net/tipc/crypto.c)

Without this guard, in-place crypto on shared skb data leads to:
  - Silent data corruption of other skb clones
  - Use-after-free when the crypto API scatterwalk writes through a
    page that has already been freed by another clone's kfree_skb()
  - Kernel crashes under concurrent 802.15.4 traffic with security
    enabled (KASAN/KMSAN reports slab-use-after-free)

Found by 0sec ( https://0sec.ai ) using automated source analysis.

Fixes: 4c14a2f ("mac802154: add llsec decryption method")
Fixes: 03556e4 ("mac802154: add llsec encryption method")
Cc: stable@vger.kernel.org
Reported-by: Doruk Tan Ozturk <doruk@0sec.ai>
Closes: https://lore.kernel.org/linux-wpan/20260525161806.96158-1-doruk@0sec.ai/
Reviewed-by: Alexander Lobakin <aleksander.lobakin@intel.com>
Signed-off-by: Doruk Tan Ozturk <doruk@0sec.ai>
Closes: <link to your mail on lore>
Link: https://lore.kernel.org/20260526183726.56100-1-doruk@0sec.ai
Signed-off-by: Stefan Schmidt <stefan@datenfreihafen.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  net/ipv4/esp4.c
  net/ipv6/esp6.c
  drivers/net/macsec.c
  drivers/net/wireguard/receive.c
  net/tipc/crypto.c
  net/mac802154/llsec.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=3a2b378b3a9ca75d3518d879148d2ad25b5714a9

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

The original Linux kernel CVE announcement for CVE-2026-63831 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-63831

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:A/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:H
  The Best / paranoid CVSS vector: AV:A/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H
  The Best / paranoid CVSS score: 7.5

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: 5
  Paranoid ActionableScore: 8

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: IMPORTANT
KPANIC detected for this report: YES
Published priority for this report (same as in Subject): IMPORTANT

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).