[CVE-2026-68405][LOW] wifi: mac80211: free AP_VLAN bc_buf SKBs outside IRQ lock [ Upstream

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

CVE: CVE-2026-68405
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: wifi: mac80211: free AP_VLAN bc_buf SKBs outside IRQ lock [ Upstream
Commit: be9dfcb0654c1f6c0fce7ba2a909683bb6f1e0ef
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=be9dfcb0654c1f6c0fce7ba2a909683bb6f1e0ef
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-68405
Analysis date: Mon, 10 Aug 2026 15:51:46 -0400
ActionableScore: 2
ActionableScore lower bound: 0
Actionable bucket: Ordinary Moderate / Low-like
Manual review required: NO

Summary:
mac80211 AP_VLAN teardown can free TX status SKBs while holding an IRQ disabled bc_buf lock, allowing a local privileged or delegated CAP_NET_ADMIN actor to trigger a softirq warning and possible DoS on panic_on_warn systems.

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

The original Linux kernel CVE announcement for CVE-2026-68405 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-68405

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: LOW
Manual review required: NO

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
======================================================================

CVE-2026-68405	LOW	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:N/I:N/A:H';CWE-667;CWE-362;CWE-703;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '4.7';DESCR 'mac80211 AP_VLAN stop can call ieee80211_free_txskb() while holding ps bc_buf lock with IRQs disabled. For SKBs with TX status state this free path can report a dropped frame through cfg80211 and nl80211 and can reach netlink tap transmit, which may trigger a softirq warning in an invalid context. The realistic impact is local denial of service only, mainly a kernel warning or crash on systems configured to panic on warnings. For the CVSS the PR:L is used for the paranoid score because some deployments may delegate CAP_NET_ADMIN to a container root or service account that is less privileged than full host root. The issue is not directly network reachable because the decisive operation is AP_VLAN interface stop through the local control plane, although wireless traffic may help create queued SKBs before the stop path runs.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate / Low-like (with actual score 1)	YES	REMOTE INIT SKB HARDWARE PACKET  DECREASED_TO_MODERATE_REGULAR_FROM_MODERATE7_BASED_ON_GUESSCVSS_AND_CIANNH DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_ACTIONABLESCORELESSTHAN3	NO	NO	checked

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

ActionableScore=2
ActionableScoreLower=0

## 1. ActionableScore

* Conservative score: 0
* Paranoid score: 2
* Final recommended bucket: **Ordinary Moderate / Low-like**

## 2. Signal breakdown

Conservative signals:

* Requires admin/root/CAP_NET_ADMIN in typical deployments: -2. Stopping or managing AP_VLAN interfaces is normally a local wireless control-plane operation requiring administrative network privileges.
* Hard or special timing/state required: -1. The warning requires AP_VLAN stop while suitable multicast or management SKBs with TX status state are present in the parent AP bc_buf.
* Availability impact realistic: +1. The described failure is a kernel softirq warning, with crash mainly on panic_on_warn systems.
* No memory corruption signal: +0. The patch moves skb freeing outside an IRQ-disabled spinlock. It does not show UAF, OOB write, double free, object replacement, callback corruption, or attacker-controlled overwrite.

Paranoid signals:

* Reliable kernel crash / strong DoS: +1. Counted only for environments where WARN_ON can become a host crash through panic_on_warn or strict production policies.
* Broad/common subsystem exposure: +1. mac80211 is a common WiFi subsystem, although this specific AP_VLAN path is configuration dependent.
* CAP_NET_ADMIN delegation penalty reduced: 0 instead of -2. In some deployments CAP_NET_ADMIN may be delegated to container root or a service account, so the trigger may be less privileged than full host root.
* Special AP_VLAN and queued SKB state still limits exploitability: no extra escalation signal.

No signals for privilege escalation, confidentiality, integrity, generic memory corruption, real lifetime corruption, or network-triggerable exploitation are supported by the patch.

## 3. Reachability analysis

The decisive trigger is local control-plane AP_VLAN stop, not packet reception alone. A remote wireless client may help create queued SKBs, but cannot directly perform the vulnerable stop operation without local administrative control of the WiFi interface. In typical deployments this requires root or CAP_NET_ADMIN. Namespaces or containers can matter only if CAP_NET_ADMIN or WiFi device control is delegated, which justifies the paranoid interpretation but not an Important-class score. The affected configuration is not a default ordinary client path, because it depends on AP mode with AP_VLAN behavior and queued TX-status SKBs.

## 4. Severity interpretation

This behaves like an ordinary Moderate or Low-like local DoS issue. The theoretical worst case is a local crash on systems configured to panic on warnings. Realistic exploitation evidence points to invalid-context freeing and a softirq warning, not memory corruption or privilege escalation. There is no demonstrated UAF reclaim, stale object reuse, write-after-free, type confusion, arbitrary write, or information disclosure primitive.

## 5. One-sentence report phrase

mac80211 AP_VLAN teardown can free TX status SKBs while holding an IRQ disabled bc_buf lock, allowing a local privileged or delegated CAP_NET_ADMIN actor to trigger a softirq warning and possible DoS on panic_on_warn systems.

## 6. Manual review recommendation

NO MANUAL CHECK NEEDED.

This can be auto-closed for urgent manual triage purposes unless the target product commonly delegates WiFi AP_VLAN management to untrusted users or runs with panic_on_warn enabled.

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

Patch: wifi: mac80211: free AP_VLAN bc_buf SKBs outside IRQ lock [ Upstream
Commit: be9dfcb0654c1f6c0fce7ba2a909683bb6f1e0ef
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=be9dfcb0654c1f6c0fce7ba2a909683bb6f1e0ef

Changed files:
  kernel/softirq.c
  net/mac80211/iface.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=be9dfcb0654c1f6c0fce7ba2a909683bb6f1e0ef

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

The original Linux kernel CVE announcement for CVE-2026-68405 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-68405

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:L
  The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS score: 4.7

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: 0
  Paranoid ActionableScore: 2

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: LOW
KPANIC detected for this report: NO
Published priority for this report (same as in Subject): LOW

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).