[CVE-2026-64570][MODERATE 7.0] wifi: mac80211: fix fils_discovery double free on alloc failure [ Upstream

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

CVE: CVE-2026-64570
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: wifi: mac80211: fix fils_discovery double free on alloc failure [ Upstream
Commit: e2c55079155a953db669ca1986a985fa286bad95
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=e2c55079155a953db669ca1986a985fa286bad95
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64570
Analysis date: Wed, 05 Aug 2026 05:22:11 -0400
ActionableScore: 5
ActionableScore lower bound: 3
Actionable bucket: Strong Important candidate / Actionable Moderate at minimum
Manual review required: YES

Summary:
A local CAP_NET_ADMIN reachable mac80211 FILS discovery update can leave a stale RCU pointer after allocation failure, causing a later update or AP teardown to double-free the same object and potentially crash the kernel.

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

The original Linux kernel CVE announcement for CVE-2026-64570 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64570

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-2026-64570	MODERATE	CHECK WITH IMPACT FROM ORIG NN IMPORTANT	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-415;*CWE-416;CWE-703;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '7';DESCR 'mac80211 FILS discovery update can double-free an RCU object when ieee80211_set_fils_discovery() queues the old template with kfree_rcu() before allocating the replacement and kzalloc() then fails. The stale link u ap fils_discovery pointer can be reused by a later update or AP teardown and the same rcu_head can be queued again, leading to KASAN double-free in RCU softirq processing and likely kernel crash. For the CVSS the PR:L value is used in the paranoid score because CAP_NET_ADMIN may be delegated to a reduced-privilege service, container root, or WiFi management process rather than full host root. The issue is local control-plane only and is not directly network reachable through WiFi frames. Impact is at least local denial of service via kernel crash and in worst case may allow confidentiality or integrity impact due to double-free memory corruption, so it should be reviewed manually.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 4)	YES	REMOTE OOB DANGER UAF  DECREASED_TO_MODERATE70_BASED_ON_ACTIONABLESCORELOWERTHAN7 DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5	YES	NO	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=5
ActionableScoreLower=3

## 1. ActionableScore

* Conservative score: 3
* Paranoid score: 5
* Final recommended bucket: **Strong Important candidate / Actionable Moderate at minimum**::

## 2. Signal breakdown

Conservative signals:

* Memory corruption, strong corruption primitive: +2. The patch fixes a confirmed double free of an RCU-freed kmalloc object.
* Real lifetime corruption: +1. The old FILS discovery object remains referenced after being queued for kfree_rcu().
* Reliable kernel crash / strong DoS: +1. The commit shows KASAN catching a double-free in rcu_free_sheaf().
* Broad/common subsystem exposure: +1. mac80211 is a common WiFi subsystem, although this specific AP/FILS path is narrower.
* Hard or special triggering condition: -1. Triggering requires kzalloc() failure after the old object was queued for RCU free.
* Privilege-gated control path: -1 conservative practical penalty. The operation normally requires CAP_NET_ADMIN or control of a WiFi management component.

Paranoid-only signals:

* Weak LPE concern: +1. Double-free memory corruption can sometimes become exploitable if object reuse is controllable, but the patch does not demonstrate reclaim, callback control, or arbitrary write.
* Confidentiality impact plausible: +1 paranoid only.
* Integrity impact plausible: +1 paranoid only.
* Same privilege and allocation-failure penalties retained: -2 total.

No remote/network-triggerable bonus is applied. This is not directly triggerable by WiFi frames.

## 3. Reachability analysis

The likely trigger is local control-plane access to mac80211 AP configuration, probably through nl80211/cfg80211 paths requiring CAP_NET_ADMIN or a privileged WiFi management service. Namespace delegation can matter if a reduced-privilege container, service account, or sandboxed root can control the relevant wireless interface, but this is not normally reachable by an arbitrary unprivileged user. The affected code is not a packet receive path and does not appear directly network-triggerable. Reliable exploitation also depends on inducing allocation failure at the right point and then causing a later update or AP teardown.

Call-site confidence: high. The patch and commit directly identify ieee80211_set_fils_discovery(), the stale pointer, the later ieee80211_stop_ap() path, and the observed RCU double-free.

## 4. Severity interpretation

This is more than an ordinary Moderate correctness bug because it is a real double-free/lifetime issue in kernel memory. Realistically, the most demonstrated impact is local DoS through allocator/RCU double-free detection or kernel crash. Theoretical escalation is possible because double-free is a memory corruption class, but the patch does not show attacker-controlled reclaim, replacement object control, callback dispatch, or arbitrary write. Therefore the conservative score stays borderline, while the paranoid score reaches Actionable Moderate.

## 5. One-sentence report phrase

A local CAP_NET_ADMIN reachable mac80211 FILS discovery update can leave a stale RCU pointer after allocation failure, causing a later update or AP teardown to double-free the same object and potentially crash the kernel.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED. YES REQUIRES MANUAL CHECK.

Reason: confirmed double-free memory corruption with RCU lifetime involvement should not be auto-closed, even though practical exploitation appears gated by CAP_NET_ADMIN and allocation-failure timing.

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

Patch: wifi: mac80211: fix fils_discovery double free on alloc failure [ Upstream
Commit: e2c55079155a953db669ca1986a985fa286bad95
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=e2c55079155a953db669ca1986a985fa286bad95

Changed files:
  mm/slub.c
  kernel/rcu/tree.c
  kernel/softirq.c
  net/mac80211/cfg.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=e2c55079155a953db669ca1986a985fa286bad95

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

The original Linux kernel CVE announcement for CVE-2026-64570 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64570

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: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: 3
  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: NO
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).