[CVE-2026-63866][IMPORTANT] wifi: mt76: mt7996: Clear wcid pointer in mt7996_mac_sta_deinit_link() [ Upstream

[CVE-2026-63866][IMPORTANT] wifi: mt76: mt7996: Clear wcid pointer in mt7996_mac_sta_deinit_link() [ Upstream

[AL-KERNEL]

CVE: CVE-2026-63866
Priority: IMPORTANT
AL-KERNEL base severity: IMPORTANT
KPANIC flag: YES
Patch: wifi: mt76: mt7996: Clear wcid pointer in mt7996_mac_sta_deinit_link() [ Upstream
Commit: 455a48685feebf2d9c1656caad77f9ba1da7b06e
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=455a48685feebf2d9c1656caad77f9ba1da7b06e
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-63866
Analysis date: Sun, 19 Jul 2026 11:32:31 -0400
ActionableScore: 7
ActionableScore lower bound: 5
Actionable bucket: Strong Important candidate / Actionable Moderate at minimum
Manual review required: YES

Summary:
A stale RCU-published WCID pointer in the mt7996 station link deinit path can remain reachable after WCID cleanup, making this an adjacent-network UAF candidate with likely DoS impact and possible higher impact if stale object reuse is feasible.

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

The original Linux kernel CVE announcement for CVE-2026-63866 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-63866

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.

======================================================================
AL-KERNEL CLASSIFICATION RESULT
======================================================================

CVE-2026-63866	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-825;*CWE-664;Other CVSS 'AV:A/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '7.5';DESCR 'A stale WCID pointer in the mt7996 station link deinit path can remain in dev mt76 wcid after a station link is removed and the WCID is cleaned up. Later TX RX or RCU based lookup paths may observe the old pointer and access freed or reinitialized station state, making this a use after free candidate rather than a pure logic bug. A wireless peer in radio range may influence station link add remove and disconnect flows, especially on an AP using mt7996 hardware, so the practical attack surface is adjacent network rather than Internet reachable. For the CVSS the PR:N because the paranoid score treats the trigger as possible from a wireless peer without local code execution or an account on the target. Impact is at least denial of service via crash and in worst case may include confidentiality or integrity impact if the stale pointer can be turned into usable memory corruption.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 7)  SKIP CVE-2026-63866 UNKNOWN SKIP No affected files built, so skip this CVE NO  - - unknown 	MAYBE	REMOTE SIMPLEFIX NETWORK KPANIC  KPANIC INCREASED_TO_HIGH_BASED_ON_GUESSCVSS	-	-	checked

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

ActionableScore=7
ActionableScoreLower=5

## 1. ActionableScore

* Conservative score: 5
* Paranoid score: 7
* Final recommended bucket: **Strong Important candidate / Actionable Moderate at minimum**::

## 2. Signal breakdown

Conservative score signals:

* Remote reachable / network-triggerable: +2
  Wireless peer behavior can plausibly influence station link removal paths on an AP or wireless device using mt7996. This is adjacent-network reachable, not Internet-reachable.
* Memory corruption, weak/indirect corruption candidate: +1
  The patch clears an RCU-published WCID pointer before cleanup. Leaving it stale is a plausible stale-pointer/UAF candidate, but the provided patch does not show reclaim control, overwrite, or callback control.
* Real lifetime corruption: +1
  The bug is a lifetime/order issue: a pointer remains published in `dev->mt76.wcid[]` while the WCID is being cleaned up.
* Reliable kernel crash / strong DoS: +1
  Later TX/RX or RCU lookup paths can plausibly dereference the stale WCID pointer and crash the kernel.

Paranoid additional interpretation:

* Generic memory corruption, stronger UAF candidate: +1 additional over conservative
  The stale WCID pointer is in a shared driver lookup table and may be reachable after cleanup, so manual review should treat it as a real UAF candidate.
* Weak LPE concern: +1
  No exploit primitive is demonstrated, but stale pointer reuse in a network-adjacent kernel driver path can sometimes become more than DoS if object reuse is controllable.

No extra points were added for public Internet exposure, arbitrary write, confirmed info leak, or demonstrated privilege escalation.

## 3. Reachability analysis

A realistic trigger would likely require a system with affected MediaTek mt7996 Wi-Fi hardware and station link add/remove or disconnect activity. The attacker model is best described as adjacent network: a wireless peer in radio range may be able to influence connection teardown or station removal behavior, especially against an AP.

No local Linux account is required in the paranoid interpretation if the trigger is reachable through wireless peer behavior. This is not a generic Internet remote issue. It is hardware and role dependent, and exposure depends on whether the affected driver is used in AP/client scenarios where untrusted peers can cause station lifecycle transitions.

Namespaces and containers are not the main factor here because the likely trigger is via wireless protocol behavior rather than a local userspace control-plane API. Call-site confidence: medium. The immediate patch shows the stale pointer cleanup site, but the full reader paths of `dev->mt76.wcid[]` are not included in the input.

## 4. Severity interpretation

This is more than an ordinary Moderate cleanup because the patch removes a stale RCU-published pointer before WCID cleanup. The realistic impact is likely kernel crash or device/host DoS. The theoretical risk is higher because stale pointer lifetime bugs in network-adjacent driver paths can become UAF exploitation candidates, even though this patch alone does not demonstrate reclaim control, write-after-free, or privilege escalation.

Conservative handling: Actionable Moderate.
Paranoid handling: Strong Important candidate for manual review.

## 5. One-sentence report phrase

A stale RCU-published WCID pointer in the mt7996 station link deinit path can remain reachable after WCID cleanup, making this an adjacent-network UAF candidate with likely DoS impact and possible higher impact if stale object reuse is feasible.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

Reason: the patch fixes a stale pointer in a network-adjacent Wi-Fi driver lifetime path. Even though only DoS is clearly supported by the provided diff, the UAF candidate should not be auto-closed without checking WCID lookup readers, RCU grace-period behavior, station teardown ordering, and whether wireless peers can reliably trigger reuse after cleanup.

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

Patch: wifi: mt76: mt7996: Clear wcid pointer in mt7996_mac_sta_deinit_link() [ Upstream
Commit: 455a48685feebf2d9c1656caad77f9ba1da7b06e
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=455a48685feebf2d9c1656caad77f9ba1da7b06e

Changed files:
  drivers/net/wireless/mediatek/mt76/mt7996/main.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=455a48685feebf2d9c1656caad77f9ba1da7b06e

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

The original Linux kernel CVE announcement for CVE-2026-63866 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-63866

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:N/I:N/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: 7

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).