[CVE-2026-68193][MODERATE REGULAR] wifi: mt76: mt7925: drop TXRX_NOTIFY on non-mmio buses

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

CVE: CVE-2026-68193
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: wifi: mt76: mt7925: drop TXRX_NOTIFY on non-mmio buses
Commit: 0c8c4cd0ca60b45c4b05a39e3769b8473d6836eb
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=0c8c4cd0ca60b45c4b05a39e3769b8473d6836eb
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-68193
Analysis date: Mon, 10 Aug 2026 15:43:07 -0400
ActionableScore: 3
ActionableScore lower bound: 1
Actionable bucket: Borderline Moderate. Manual check required for adjacent wireless or firmware mediated reachability
Manual review required: YES

Summary:
A TXRX_NOTIFY event on mt7925 non-mmio devices can reach a NULL tx_cleanup callback in the RX worker and crash the kernel, with practical impact depending on whether the event can be induced by firmware, malicious hardware, or adjacent wireless activity.

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

The original Linux kernel CVE announcement for CVE-2026-68193 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-68193

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 REGULAR
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-2026-68193	MODERATE	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:N/I:N/A:H';**CWE-476;*CWE-20;CWE-754;Other CVSS 'AV:P/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:H';BEST CVSS score: '5.3';DESCR 'A NULL function pointer dereference in the mt7925 RX path can occur because PKT_TYPE_TXRX_NOTIFY is an MMIO only event but it was handled on non-mmio buses as well. On USB devices mt7925_mac_tx_free can reach mt76_queue_tx_cleanup() and then queue_ops tx_cleanup, which is NULL for this bus type, causing a kernel crash in the RX worker. For the CVSS the PR:N is used in the paranoid score because the attacker model does not require a local account on the victim if the trigger is a malicious attached device or a possible adjacent wireless condition. The issue is not clearly reachable from normal network traffic and practical exploitation likely requires a malicious or faulty USB WiFi device, compromised firmware, or a still unconfirmed adjacent wireless trigger. Impact is denial of service only via kernel crash.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline Moderate. Manual check required for adjacent wireless or firmware mediated reachability (with actual score 2)	YES	REMOTE DANGER NULLPTR INIT SIMPLEFIX NETWORK SKB DMAorINTERRUPT HARDWARE  DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5	YES	NO	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=3
ActionableScoreLower=1

## 1. ActionableScore

* Conservative score: 1
* Paranoid score: 3
* Final recommended bucket: **Borderline Moderate. Manual check required for adjacent wireless or firmware mediated reachability**

## 2. Signal breakdown

Conservative scoring:

* Firmware-mediated external influence: +1. The bad event is generated in the mt7925 RX path and may depend on device or firmware behavior rather than ordinary local code.
* Reliable kernel crash / strong DoS: +1. The commit shows a direct NULL function pointer call through queue_ops->tx_cleanup and a kernel NULL pointer dereference in mt76u_rx_worker.
* Physical-only or rare hardware-only condition: -1. The issue is specific to mt7925 on non-mmio buses such as USB and is not shown to be triggerable by normal WiFi traffic.

Paranoid scoring:

* Firmware-mediated external influence: +1. A malicious or compromised device or firmware could plausibly emit TXRX_NOTIFY on a non-mmio bus.
* Reliable kernel crash / strong DoS: +1. The crash path is explicit and direct.
* Availability impact realistic: +1. If the event can be induced repeatedly, the result is host kernel crash or repeated system-wide DoS.
* No generic memory corruption points. This is a NULL function pointer dereference to address 0, not UAF, OOB write, type confusion, or controlled callback corruption.
* No privilege escalation points. The patch does not show attacker-controlled reclaim, write primitive, object replacement, or function pointer control.

## 3. Reachability analysis

The most realistic trigger is a faulty, malicious, or compromised mt7925 USB device or firmware sending an MMIO-only TXRX_NOTIFY event on a non-mmio bus. A local user account is not clearly required in that model, but physical device control or firmware influence may be required.

Normal remote network reachability is not demonstrated. The patch does not prove that crafted WiFi frames from an adjacent attacker can force the device to emit this event. That uncertainty is why the conservative score stays low while the paranoid score keeps the issue in manual-review territory.

Namespaces and containers do not materially lower the privilege requirement unless a container can control the affected USB WiFi device or trigger firmware behavior. The affected path is hardware and driver specific, not a broad default kernel networking path.

## 4. Severity interpretation

This behaves primarily like a driver-specific DoS issue, not an Important-class memory corruption vulnerability. The crash primitive is strong and explicit, but the exploit primitive is limited to a NULL callback invocation with no evidence of controlled memory corruption, confidentiality impact, integrity impact, or LPE.

The main triage question is reachability. If further review shows that adjacent WiFi traffic can reliably trigger TXRX_NOTIFY on USB mt7925 devices, the issue becomes an Actionable Moderate wireless-adjacent DoS. If only malicious hardware or faulty firmware can trigger it, it remains ordinary Moderate or Low-like.

## 5. One-sentence report phrase

A TXRX_NOTIFY event on mt7925 non-mmio devices can reach a NULL tx_cleanup callback in the RX worker and crash the kernel, with practical impact depending on whether the event can be induced by firmware, malicious hardware, or adjacent wireless activity.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

Manual review is needed to determine whether TXRX_NOTIFY can be induced by crafted adjacent WiFi traffic or only by faulty or malicious device firmware. This distinction controls whether the bug is merely hardware-mediated DoS or an actionable wireless-adjacent DoS.

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

Patch: wifi: mt76: mt7925: drop TXRX_NOTIFY on non-mmio buses
Commit: 0c8c4cd0ca60b45c4b05a39e3769b8473d6836eb
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=0c8c4cd0ca60b45c4b05a39e3769b8473d6836eb

Commit description:

PKT_TYPE_TXRX_NOTIFY is an mmio-only event, but mt7925_rx_check() and
mt7925_queue_rx_skb() dispatch it to mt7925_mac_tx_free() on every bus.
mt7925_mac_tx_free() cleans the DMA tx queues with
mt76_queue_tx_cleanup(), which calls queue_ops->tx_cleanup(). Only the
mmio queue ops implement that callback; on USB it is NULL, so a
TXRX_NOTIFY there calls a NULL pointer in the RX worker:

  BUG: kernel NULL pointer dereference, address: 0000000000000000
  RIP: 0010:0x0
  Call Trace:
   mt7925_mac_tx_free+0x58/0x350 [mt7925_common]
   mt7925_rx_check+0xe2/0x130 [mt7925_common]
   mt76u_rx_worker+0x1b9/0x620 [mt76_usb]

Drop the event on non-mmio buses via mt76_is_mmio(), as in
commit 5683e14 ("wifi: mt76: connac: do not check WED status for
non-mmio devices").

Fixes: c948b5d ("wifi: mt76: mt7925: add Mediatek Wi-Fi7 driver for mt7925 chips")
Cc: stable@vger.kernel.org
Signed-off-by: Devin Wittmayer <lucid_duck@justthetip.ca>
Link: https://patch.msgid.link/20260627191336.20223-3-lucid_duck@justthetip.ca
Signed-off-by: Felix Fietkau <nbd@nbd.name>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  drivers/net/wireless/mediatek/mt76/mt7925/mac.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=0c8c4cd0ca60b45c4b05a39e3769b8473d6836eb

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

The original Linux kernel CVE announcement for CVE-2026-68193 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-68193

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:P/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS vector: AV:A/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS score: 5.3

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: 1
  Paranoid ActionableScore: 3

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 REGULAR

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).