[CVE-2026-72073][MODERATE 7.0] mmc: vub300: fix use-after-free on probe failure [ Upstream

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

CVE: CVE-2026-72073
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: mmc: vub300: fix use-after-free on probe failure [ Upstream
Commit: 5b82af744e06cd741938c3da54fdbe564a7e52d9
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=5b82af744e06cd741938c3da54fdbe564a7e52d9
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72073
Analysis date: Sun, 16 Aug 2026 06:01:40 -0400
ActionableScore: 5
ActionableScore lower bound: 2
Actionable bucket: Actionable Moderate at minimum
Manual review required: YES

Summary:
A race in the vub300 probe failure path can free the mmc host while timer-queued deadwork still references the same controller state, causing a physical-device-triggerable use-after-free and likely kernel crash.

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ABOUT THIS REPORT
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The original Linux kernel CVE announcement for CVE-2026-72073 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72073

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.

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AL-KERNEL CLASSIFICATION RESULT
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CVE-2026-72073	MODERATE	CHECK WITH IMPACT FROM ORIG NN IMPORTANT	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:P/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H';*CWE-416;CWE-362;*CWE-672;Other CVSS 'AV:P/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '6.4';DESCR 'A use after free race can occur in the mmc vub300 probe failure path when the inactivity timer has already been armed and mmc_add_host later fails. The timer callback may queue deadwork and hold a kref while the probe error path directly frees the mmc host and the backing vub300 storage, allowing queued work to access freed memory. For the CVSS the PR:N is used because no authenticated user privileges are required if the attacker can present a malicious or failing USB device to the target. The issue is not network reachable and normally requires physical or equivalent local USB device access. Impact is at least denial of service via kernel crash and in the paranoid case may include confidentiality and integrity impact because the bug class is UAF memory corruption.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate at minimum (with actual score 4)	YES	RACE ERRORPATH UAF TIMER LINUS  LOWERED_FROM_HIGH_BASED_ON_GUESSCVSS  DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5	YES	NO	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=5
ActionableScoreLower=2

## 1. ActionableScore

* Conservative score: 2
* Paranoid score: 5
* Final recommended bucket: **Actionable Moderate at minimum**::

## 2. Signal breakdown

Conservative signals:

* Firmware-mediated or device-mediated external influence: +1
  A malicious or failing USB vub300 device can plausibly influence probe timing and failure behavior.
* Memory corruption, weak primitive: +1
  This is a real UAF, but the trigger is race-dependent and no controlled reclaim, overwrite, or type confusion is shown.
* Real lifetime corruption: +1
  The probe error path bypasses the kref lifetime model and directly frees the backing mmc host while queued work may still hold references.
* Reliable kernel crash / strong DoS: +1
  If the race is hit, queued deadwork can dereference freed vub300 storage and crash the kernel.
* Hard or unreliable race / special timing required: -1
  mmc_add_host() must fail and take more than about one second after the inactivity timer is armed.
* Physical-only or rare hardware-only condition: -2
  Practical triggering normally requires physical or equivalent USB device access and the vub300 hardware path is uncommon.

Paranoid additional interpretation:

* Generic memory corruption, UAF class: +1 additional over conservative
  The freed object can be accessed asynchronously by workqueue context after mmc_free_host(), so manual review should not treat it as a pure NULL dereference.
* Confidentiality impact plausible: +1
  Not demonstrated, but UAF memory reuse can theoretically expose stale kernel data in some layouts.
* Integrity impact plausible: +1
  Not demonstrated, but UAF memory reuse can theoretically corrupt kernel object state.

Call-site confidence: high. The commit message gives the exact probe thread versus timer/workqueue sequence and the patch changes the relevant error path directly.

## 3. Reachability analysis

The bug is not network reachable. The realistic attacker model is physical or equivalent local device access, for example presenting a malicious, faulty, or timing-sensitive USB vub300 device that causes probe to arm the inactivity timer and later fail in mmc_add_host(). No local Linux user privileges are required if the attacker can physically attach the device, but exploitation depends on rare hardware and a narrow timing window. Namespaces and containers do not materially lower the requirement because the vulnerable path is USB device probing in the host kernel, not a namespaced userspace API.

## 4. Severity interpretation

This is not an ordinary resource leak or validation-only fix. It is a genuine lifetime bug with a queued work item accessing storage after the probe error path directly frees the mmc host. Realistic exploitation looks mostly like a difficult physical-device-triggered kernel crash, so the conservative score remains low. The paranoid score is higher because UAF in asynchronous workqueue context is a memory corruption class that should not be auto-closed without manual review, even though no strong LPE primitive is demonstrated.

## 5. One-sentence report phrase

A race in the vub300 probe failure path can free the mmc host while timer-queued deadwork still references the same controller state, causing a physical-device-triggerable use-after-free and likely kernel crash.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED. YES REQUIRES MANUAL CHECK.

Reason: this is a real UAF race in driver lifetime management, but practical severity depends heavily on whether the affected product exposes vub300 USB devices or similar physical-device attack paths.

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

Patch: mmc: vub300: fix use-after-free on probe failure [ Upstream
Commit: 5b82af744e06cd741938c3da54fdbe564a7e52d9
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=5b82af744e06cd741938c3da54fdbe564a7e52d9

Changed files:
  drivers/mmc/host/vub300.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=5b82af744e06cd741938c3da54fdbe564a7e52d9

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

The original Linux kernel CVE announcement for CVE-2026-72073 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72073

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:H/PR:N/UI:N/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS vector: AV:P/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H
  The Best / paranoid CVSS score: 6.4

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: 2
  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).