[CVE-2026-72391][LOW] net: phy: sfp: free mii_bus in sfp_i2c_mdiobus_destroy [ Upstream

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

CVE: CVE-2026-72391
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: net: phy: sfp: free mii_bus in sfp_i2c_mdiobus_destroy [ Upstream
Commit: 92dd9a522f01ef57f633a8c1953cf6d48ef2bcd5
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=92dd9a522f01ef57f633a8c1953cf6d48ef2bcd5
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72391
Analysis date: Sun, 16 Aug 2026 00:16:04 -0400
ActionableScore: 0
ActionableScore lower bound: unknown
Actionable bucket: Ordinary Moderate / Low-like
Manual review required: YES

Summary:
No one-sentence report phrase was found.

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

The original Linux kernel CVE announcement for CVE-2026-72391 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72391

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: YES

A detailed explanation of the methodology and priority rules is included
at the end of this message.

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

CVE-2026-72391	LOW	CHECK WITH IMPACT FROM ORIG NN MODERATE	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-401;*CWE-772;**CWE-400;Other CVSS 'AV:P/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '4.6';DESCR 'A memory leak in the SFP I2C MDIO bus teardown path occurs because sfp_i2c_mdiobus_destroy unregisters sfp i2c_mii but does not free the non devm mii_bus allocated by mdio_i2c_alloc. The leak is triggered when a copper or RollBall SFP module that created an MDIO bus is physically removed, because the hot removal path clears the only stored reference after unregistering the bus. For the CVSS the PR:N is used for the paranoid score because physical access to remove the module does not require OS privileges, while the attack vector remains physical rather than network reachable. Impact is resource exhaustion only after repeated module removal events. There is no evidence of UAF, OOB access, information disclosure, or privilege escalation.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate / Low-like (with actual score 0)  SKIP CVE-2026-72391 UNKNOWN SKIP No affected files built, so skip this CVE NO  - - unknown 	MAYBE	INIT SIMPLEFIX LEAK NETWORK  DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5 DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_ACTIONABLESCORELESSTHAN3	-	-	checked

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

ActionableScore=0

1. ActionableScore
* Conservative score: 0
* Paranoid score: 0
* Final recommended bucket: **Ordinary Moderate / Low-like**

2. Signal breakdown
* Availability impact realistic: +1. Repeated hot-removal of affected copper/RollBall SFP modules can leak `struct mii_bus` objects and may eventually contribute to memory pressure.
* Physical-only or rare hardware-only condition: -2. The trigger requires physical SFP module removal or equivalent hardware hotplug behavior.
* No remote/network-triggerable signal. Packet traffic alone does not appear to trigger the leak.
* No local unprivileged software trigger. A local user cannot normally cause this path without physical access or privileged device control.
* No memory corruption signal. The patch fixes a missing `mdiobus_free()` after `mdiobus_unregister()`, which is a resource leak, not UAF, OOB write, double free, or type confusion.
* No LPE signal. There is no attacker-controlled reclaim, overwrite, callback control, stale object reuse, or privilege boundary bypass.
* Call-site confidence: high. The commit identifies the allocation path, teardown path, and hot-removal condition.

3. Reachability analysis
The bug is reachable when a copper or RollBall SFP module creates an I2C MDIO bus and is then physically removed. Typical exploitation requires physical access to the hardware or privileged control over equivalent hotplug events. Namespaces and containers do not meaningfully lower the privilege requirement because this is not a normal namespace-exposed software API. The affected path is only relevant on systems with suitable SFP hardware and modules, so exposure is configuration and hardware dependent.

4. Severity interpretation
This behaves like a Low-like or ordinary Moderate resource leak, not an actionable Moderate or Important kernel vulnerability. The realistic impact is gradual resource exhaustion after repeated physical hot-removal events. Theoretical DoS exists, but there is no evidence of memory corruption, confidentiality impact, integrity impact, or privilege escalation.

5. One-sentence report phrase
A missing `mdiobus_free()` in the SFP I2C MDIO bus hot-removal path leaks `struct mii_bus` objects when affected copper or RollBall SFP modules are removed, with impact limited to potential resource exhaustion after repeated physical events.

6. Manual review recommendation
NO MANUAL CHECK NEEDED.
NO MANUAL CHECK REQUIRED COULD BE AUTOCLOSED.
This is a straightforward physical-triggered resource leak with no supported memory corruption or privilege escalation primitive.

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

Patch: net: phy: sfp: free mii_bus in sfp_i2c_mdiobus_destroy [ Upstream
Commit: 92dd9a522f01ef57f633a8c1953cf6d48ef2bcd5
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=92dd9a522f01ef57f633a8c1953cf6d48ef2bcd5

Changed files:
  drivers/net/phy/sfp.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=92dd9a522f01ef57f633a8c1953cf6d48ef2bcd5

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

The original Linux kernel CVE announcement for CVE-2026-72391 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72391

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: unknown
  Paranoid ActionableScore: 0

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).