[CVE-2026-46136][LOW] wifi: mt76: mt7921: fix a potential clc buffer length underflow

[CVE-2026-46136][LOW] wifi: mt76: mt7921: fix a potential clc buffer length underflow

[AL-KERNEL]

CVE: CVE-2026-46136
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: wifi: mt76: mt7921: fix a potential clc buffer length underflow
Commit: e451c325b000b9a0081fd93bc6d103d6943d4b55
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=e451c325b000b9a0081fd93bc6d103d6943d4b55
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-46136
Analysis date: Thu, 28 May 2026 13:13:22 -0400
ActionableScore: 2
ActionableScore lower bound: 1
Actionable bucket: Ordinary Moderate / Low-like
Manual review required: NO

Summary:
A mt7921 CLC power table length underflow can make the driver parse with an invalid remaining buffer length, causing a near infinite loop, invalid power settings, or WiFi initialization failure without evidence of memory corruption or privilege escalation.

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ABOUT THIS REPORT
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The original Linux kernel CVE announcement for CVE-2026-46136 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-46136

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
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CVE-2026-46136	LOW	CHECK	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:P/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H';CWE-190;CWE-125;*CWE-835;*CWE-20;Other CVSS 'AV:P/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '4.6';DESCR 'mt7921 CLC power table parsing could underflow buf_len when a rule length made offset larger than the remaining buffer. This can make the parser continue with an invalid remaining length, leading to a near infinite loop, invalid power settings, or WiFi driver initialization failure. For the CVSS the PR:N is used because a malformed firmware or CLC table does not require privileges on the victim once the affected device path is active. The issue is not directly network reachable and is better treated as firmware or device data mediated input. Impact is mainly availability loss for the affected WiFi device path, with no demonstrated information disclosure, write primitive, or privilege escalation.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate / Low-like (with actual score 2) 	MAYBE	REMOTE OOB SIMPLEFIX NETWORK  DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5 DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_ACTIONABLESCORELESSTHAN3	-	-	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=2
ActionableScoreLower=1

## 1. ActionableScore

* Conservative score: **1**
* Paranoid score: **2**
* Final recommended bucket: **Ordinary Moderate / Low-like**::

## 2. Signal breakdown

* Firmware or device-data mediated influence: **+1**. The problematic CLC power table data appears to come from device or firmware calibration data, not from ordinary remote network packets.
* Availability impact realistic: **+1 paranoid**. The underflow can lead to an almost infinite loop, invalid power settings, or WiFi driver initialization failure.
* Weak OOB / parsing issue: **+0**. The patch prevents `buf_len` underflow and possible invalid parsing, but it does not show an OOB write, UAF, controlled overwrite, or data disclosure.
* Rare or device-specific exposure: **-1 conservative**. The issue is specific to mt7921 CLC table parsing and requires affected MediaTek WiFi hardware and relevant table contents.
* No confidentiality or integrity signal: **+0**. No leak path, write primitive, privilege escalation, or policy bypass is shown.

## 3. Reachability analysis

The bug is reached during mt7921 WiFi driver CLC country power table parsing, likely during device initialization or regulatory power setup. A normal remote WiFi peer is not shown to control the CLC table, so this should not be treated as network-triggerable packet parsing. Namespaces and containers do not materially change reachability because the input is device or firmware data. Realistic exploitation requires affected hardware and malformed or unexpected CLC table contents.

## 4. Severity interpretation

This behaves like a **Low-like or ordinary Moderate** issue. The practical impact is driver initialization failure or device-level DoS. Although an integer underflow may cause invalid parsing, the patch context does not support memory corruption, privilege escalation, or information disclosure. It should not be treated as Important without additional evidence that an attacker can control the CLC table or turn the invalid parsing into a stronger primitive.

## 5. One-sentence report phrase

A mt7921 CLC power table length underflow can make the driver parse with an invalid remaining buffer length, causing a near infinite loop, invalid power settings, or WiFi initialization failure without evidence of memory corruption or privilege escalation.

## 6. Manual review recommendation

**NO MANUAL CHECK NEEDED**

The issue is device-data mediated and appears limited to availability impact in a hardware-specific WiFi driver path, with no demonstrated leak, write primitive, or LPE path.

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

Patch: wifi: mt76: mt7921: fix a potential clc buffer length underflow
Commit: e451c325b000b9a0081fd93bc6d103d6943d4b55
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=e451c325b000b9a0081fd93bc6d103d6943d4b55

Commit description:

The buf_len is used to limit the iterations for retrieving the country
power setting and may underflow under certain conditions due to changes
in the power table in CLC.

This underflow leads to an almost infinite loop or an invalid power
setting resulting in driver initialization failure.

Cc: stable@vger.kernel.org
Fixes: fa6ad88 ("wifi: mt76: mt7921: fix country count limitation for CLC")
Signed-off-by: Leon Yen <leon.yen@mediatek.com>
Signed-off-by: Ming Yen Hsieh <mingyen.hsieh@mediatek.com>
Link: https://patch.msgid.link/20251009020158.1923429-1-mingyen.hsieh@mediatek.com
Signed-off-by: Felix Fietkau <nbd@nbd.name>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  drivers/net/wireless/mediatek/mt76/mt7921/mcu.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=e451c325b000b9a0081fd93bc6d103d6943d4b55

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

The original Linux kernel CVE announcement for CVE-2026-46136 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-46136

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:N/S:U/C:N/I:N/A:L
  The Best / paranoid CVSS vector: AV:P/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS score: 4.6

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: 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).