[CVE-2026-74661][MODERATE 7.0] mac802154: fix netdev use-after-free in beacon worker

[CVE-2026-74661][MODERATE 7.0] mac802154: fix netdev use-after-free in beacon worker

[AL-KERNEL]

CVE: CVE-2026-74661
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: mac802154: fix netdev use-after-free in beacon worker
Commit: fe820dcc1d8ff77783a9d2bcc93b98c99ac6d517
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=fe820dcc1d8ff77783a9d2bcc93b98c99ac6d517
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74661
Analysis date: Sat, 22 Aug 2026 14:59:18 -0400
ActionableScore: 5
ActionableScore lower bound: 4
Actionable bucket: Actionable Moderate at minimum
Manual review required: YES

Summary:
A race in the mac802154 beacon worker can leave `sdata` and embedded `wpan_dev` referenced after RCU protection is dropped and the netdev private area is freed during teardown, causing a local UAF that can crash the kernel and may warrant further review for possible privilege escalation.

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ABOUT THIS REPORT
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The original Linux kernel CVE announcement for CVE-2026-74661 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74661

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-2026-74661	MODERATE	CHECK WITH IMPACT FROM ORIG NN MODERATE	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H';*CWE-416;CWE-362;*CWE-664;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '7';DESCR 'A use after free race exists in the mac802154 beacon worker because it derives sdata and the embedded wpan_dev from local beacon_req under RCU, then drops the RCU read lock and continues using the derived netdev private data. If beacon stop or interface teardown clears the beacon request while the worker is already running, the worker can dereference freed netdev private memory. For the CVSS the PR:L is used for the paranoid score because a local process with delegated network administration or IEEE 802.15.4 management capability may be able to start or stop beaconing and tear down the interface, while full host root is not always required in containerized or service managed deployments. The issue is not directly network reachable and is triggered through local control plane operations rather than packet traffic. Impact is at least local denial of service via kernel crash and in the worst case may allow confidentiality or integrity impact due to UAF based memory corruption, so it should be reviewed manually.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate at minimum (with actual score 5)  SKIP CVE-2026-74661 UNKNOWN SKIP The Fixes patch not applied yet, so unlikely that actual: url YES  NO NO unknown 	MAYBE	UAF HARDWARE LINUS KPANIC 	-	-	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=5
ActionableScoreLower=4

## 1. ActionableScore

* Conservative score: 4
* Paranoid score: 5
* Final recommended bucket: **Actionable Moderate at minimum**

## 2. Signal breakdown

Conservative signals:

* Memory corruption, weak/indirect corruption candidate: +1
  The patch fixes an explicit use-after-free race, but does not show attacker-controlled reclaim, overwrite, callback control, or type confusion.

* Real lifetime corruption: +1
  The beacon worker drops RCU protection and continues using `sdata` and embedded `wpan_dev` after interface teardown can free the netdev private area.

* Reliable kernel crash / strong DoS: +1
  Dereferencing freed netdev private memory can realistically crash the kernel.

* Availability impact realistic: +1
  The impact is host-level kernel crash or severe instability, not only a harmless warning.

* Privileged kernel/device-management lifetime path: +1
  The bug is in network device lifetime handling with async workqueue execution and netdev teardown.

* Hard or unreliable race / special timing required: -1
  Exploitation requires the beacon worker to overlap with beacon stop or interface teardown.

* Requires CAP_NET_ADMIN or equivalent in typical deployments: -1
  Beaconing and interface teardown normally require network administration privileges, but delegated netns/container setups may reduce this below full host root.

Paranoid additional signal:

* Weak LPE concern: +1
  The UAF affects netdev private data used after RCU lifetime loss. No strong exploit primitive is demonstrated, but kernel netdev object lifetime UAFs deserve manual review for possible reclaim or object reuse paths.

## 3. Reachability analysis

The bug is locally reachable through IEEE 802.15.4/mac802154 control-plane operations involving beaconing and interface teardown. It is not directly network-triggerable by packet traffic. In typical deployments, triggering requires CAP_NET_ADMIN or a privileged network-management context. In containers or delegated network namespaces, a less trusted actor may have enough network administration capability to exercise the affected path without full host-root privileges. The subsystem is not universally enabled or commonly exposed, and realistic exploitation requires a race window between a running beacon worker and teardown.

Call-site confidence: medium. The patch and commit describe the lifetime violation clearly, but the full downstream uses of `sdata` and `wpan_dev` after the RCU unlock are not fully shown in the supplied snippet.

## 4. Severity interpretation

This is stronger than an ordinary Moderate because it is an explicit UAF race in kernel network object lifetime handling. Realistically, the demonstrated impact is local DoS through kernel crash. Theoretical privilege escalation is possible in the paranoid model because freed netdev private memory may be reused, but the patch does not demonstrate attacker-controlled reclaim, write-after-free, type confusion, or callback hijacking. Therefore this should be treated as Actionable Moderate at minimum, not auto-closed, but not a strong Important candidate without additional exploitability evidence.

## 5. One-sentence report phrase

A race in the mac802154 beacon worker can leave `sdata` and embedded `wpan_dev` referenced after RCU protection is dropped and the netdev private area is freed during teardown, causing a local UAF that can crash the kernel and may warrant further review for possible privilege escalation.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

Reason: explicit UAF race in network device lifetime handling. The known impact is DoS, but the object lifetime pattern is security-relevant enough to require manual review for reclaim, reuse, or write-after-free possibilities.

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

Patch: mac802154: fix netdev use-after-free in beacon worker
Commit: fe820dcc1d8ff77783a9d2bcc93b98c99ac6d517
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=fe820dcc1d8ff77783a9d2bcc93b98c99ac6d517

Commit description:

mac802154_beacon_worker() reads local->beacon_req under RCU and derives
the sub-interface from the request, but then drops the RCU read lock and
continues to use both sdata and the embedded wpan_dev.

mac802154_stop_beacons_locked() cancels only pending beacon work, clears
local->beacon_req and frees the request.  A beacon worker that is already
running can therefore continue after interface teardown and dereference
the freed netdev private area.

The scan worker already pins the netdev before leaving RCU.  Apply the
same lifetime rule to the beacon worker: take a netdev reference while
the request is still protected by RCU, and release it on all paths that
continue after the reference is acquired.

Fixes: 3accf47 ("mac802154: Handle basic beaconing")
Cc: stable@vger.kernel.org
Reported-by: Vega <vega@nebusec.ai>
Signed-off-by: Zihan Xi <zihanx@nebusec.ai>
Reviewed-by: Miquel Raynal <miquel.raynal@bootlin.com>
Link: https://patch.msgid.link/e9a3909c7a6281967961773ca841e860b8ecf40e.1785596603.git.zihanx@nebusec.ai
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  net/mac802154/scan.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=fe820dcc1d8ff77783a9d2bcc93b98c99ac6d517

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

The original Linux kernel CVE announcement for CVE-2026-74661 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74661

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:H
  The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/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: 4
  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: 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).