[CVE-2026-74325][MODERATE 7.0] wifi: mt76: use kfree_rcu for offchannel link in mt76_put_vif_phy_link [ Upstream

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

CVE: CVE-2026-74325
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: wifi: mt76: use kfree_rcu for offchannel link in mt76_put_vif_phy_link [ Upstream
Commit: c7a83899203ed36696a2d35ddd03c0f522874a63
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=c7a83899203ed36696a2d35ddd03c0f522874a63
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74325
Analysis date: Sat, 15 Aug 2026 04:13:19 -0400
ActionableScore: 5
ActionableScore lower bound: 3
Actionable bucket: Strong Important candidate / Actionable Moderate at minimum**:: Actionable Moderate at minimum. Not enough evidence for Strong Important without reclaim, write-after-free, callback control, or object replacement.
Manual review required: YES

Summary:
An RCU lifetime bug in mt76 offchannel link removal can let the TX datapath dereference a freed `mlink` object after `kfree()`, causing a kernel crash and requiring manual review for possible UAF exploitability beyond DoS.

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

The original Linux kernel CVE announcement for CVE-2026-74325 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74325

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.

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

CVE-2026-74325	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-416;CWE-362;*CWE-672;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '7';DESCR 'mt76 offchannel link removal can create an RCU use after free because rcu_assign_pointer clears mvif offchannel_link but the object is then released with kfree while existing RCU readers may still hold the old pointer. The TX datapath can dereference mlink wcid or mlink idx under rcu_read_lock after another context has freed the same mlink object, which can crash the kernel and may create a memory corruption candidate. For the CVSS the PR:L is used for the paranoid score because reliable triggering may be possible for a local user or local service that can generate WiFi activity while the system performs offchannel or remain_on_channel operations, even if full administrative control is not always required in real deployments. The issue is not directly reachable from the Internet, but a nearby WiFi peer may influence the TX path on affected mt76 hardware while the vulnerable lifetime race is controlled by local wireless state changes. Impact is at least local denial of service via kernel crash and in worst case may allow confidentiality or integrity impact due to kernel UAF behavior, so this 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 UAF NETWORK  DECREASED_TO_MODERATE70_BASED_ON_ACTIONABLESCORELOWERTHAN6 DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5	YES	NO	checked

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

ActionableScore=5
ActionableScoreLower=3

## 1. ActionableScore

* Conservative score: **3**
* Paranoid score: **5**
* Final recommended bucket: **Strong Important candidate / Actionable Moderate at minimum**:: Actionable Moderate at minimum. Not enough evidence for Strong Important without reclaim, write-after-free, callback control, or object replacement.

## 2. Signal breakdown

Conservative signals:

* **Memory corruption, weak primitive: +1**
  This is an RCU lifetime UAF candidate. Existing RCU readers may still dereference `mlink` after `kfree()`, but the patch shows read dereferences of `mlink->wcid` and `mlink->idx`, not an attacker-controlled write or callback hijack.

* **Real lifetime corruption: +1**
  `rcu_assign_pointer(..., NULL)` is followed by plain `kfree(mlink)`, while readers use `rcu_dereference()` under `rcu_read_lock()`. This is a real RCU lifetime mismatch.

* **Reliable kernel crash / strong DoS: +1**
  Dereferencing freed memory in the TX datapath can plausibly crash the kernel.

* **Hard or unreliable race / special timing required: -1**
  The issue requires a timing window between offchannel link removal and TX-side RCU access.

* **Local unprivileged or low-privileged trigger concern: +1**
  A local user or local network-management service may be able to generate WiFi activity while offchannel or remain-on-channel operations occur. Full host-root is not necessarily required in all practical deployments.

Paranoid additional interpretation:

* **Weak LPE concern / UAF review sensitivity: +1**
  Not counted as strong LPE. However, because this is a kernel UAF in a driver TX path, manual review is justified to check whether object reuse or controlled reclaim is possible in the real allocator context.

Paranoid cap reasoning:

* This matches the race-dependent RCU UAF class. No write-after-free, callback dispatch, type confusion, refcount takeover, or attacker-controlled reclaim is shown. Therefore the conservative score stays low, and the paranoid score is capped at **5**.

## 3. Reachability analysis

The affected path is in the mt76 WiFi driver offchannel link cleanup. Triggering requires affected mt76 hardware, offchannel or remain-on-channel state transitions, and concurrent TX datapath activity. A nearby WiFi peer may influence traffic timing, but the vulnerable lifetime transition is primarily controlled by local wireless state changes, so this is not treated as directly Internet-reachable.

Namespaces and containers generally do not make raw WiFi device control broadly available, but desktop or embedded systems often delegate wireless operations to local services such as NetworkManager or wpa_supplicant. This supports PR:L style practical concern rather than PR:H in all environments.

Call-site confidence: **medium**. The commit message identifies the relevant TX datapath example, but the full caller code is not included in the supplied diff.

## 4. Severity interpretation

This is more than an ordinary Moderate correctness issue because it is a real RCU use-after-free in kernel driver code. Realistic demonstrated impact is most likely kernel crash or device/host instability. Theoretical escalation is possible in the broad sense that kernel UAF bugs can sometimes be developed further, but the patch does not show a concrete reclaim, overwrite, callback, type confusion, or arbitrary memory access primitive.

Overall this should be treated as **Actionable Moderate at minimum**, not auto-closed as low-risk DoS. It is not a strong Important candidate on the provided evidence alone.

## 5. One-sentence report phrase

An RCU lifetime bug in mt76 offchannel link removal can let the TX datapath dereference a freed `mlink` object after `kfree()`, causing a kernel crash and requiring manual review for possible UAF exploitability beyond DoS.

## 6. Manual review recommendation

**MANUAL CHECK REQUIRED**

Reason: this is a real RCU UAF in a wireless TX path. The proven impact is likely DoS, but the UAF class and allocator-reuse uncertainty make it unsuitable for automatic closure.

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

Patch: wifi: mt76: use kfree_rcu for offchannel link in mt76_put_vif_phy_link [ Upstream
Commit: c7a83899203ed36696a2d35ddd03c0f522874a63
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=c7a83899203ed36696a2d35ddd03c0f522874a63

Changed files:
  drivers/net/wireless/mediatek/mt76/channel.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=c7a83899203ed36696a2d35ddd03c0f522874a63

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

The original Linux kernel CVE announcement for CVE-2026-74325 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74325

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).