[CVE-2026-72443][MODERATE 7.0] ALSA: usb-audio: Kill MIDI 2.0 URBs before freeing endpoints [ Upstream

[CVE-2026-72443][MODERATE 7.0] ALSA: usb-audio: Kill MIDI 2.0 URBs before freeing endpoints [ Upstream

[AL-KERNEL]

CVE: CVE-2026-72443
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: ALSA: usb-audio: Kill MIDI 2.0 URBs before freeing endpoints [ Upstream
Commit: bcdd5a7363bdd287253c406a9c0205f5722058e7
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=bcdd5a7363bdd287253c406a9c0205f5722058e7
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72443
Analysis date: Sun, 16 Aug 2026 02:46:02 -0400
ActionableScore: 5
ActionableScore lower bound: 4
Actionable bucket: Actionable Moderate at minimum
Manual review required: YES

Summary:
A malicious or faulty USB MIDI 2.0 device can trigger a probe error path where submitted input URBs complete after endpoint storage has been freed, causing a slab use-after-free in `input_urb_complete()` and likely kernel crash, with only weak theoretical privilege-escalation concern.

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

The original Linux kernel CVE announcement for CVE-2026-72443 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72443

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-2026-72443	MODERATE	CHECK WITH IMPACT FROM ORIG NN MODERATE	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-664;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 slab use after free can occur in the ALSA usb audio MIDI 2.0 input path when submitted input URBs are not killed before endpoint storage and coherent URB buffers are freed. A malicious or faulty USB MIDI 2.0 device can reach this during probe by starting input streams and then causing a later setup failure, allowing input_urb_complete to run with a stale urb context. For the CVSS the PR:N is used because no software privilege on the victim is required when the attacker can present the malicious USB device. The issue is not network reachable in the normal model and requires physical USB access or an equivalent local USB emulation path. Impact is at least denial of service via kernel crash and in the paranoid case may include confidentiality and integrity impact because the primitive is a real use after free in kernel completion context.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate at minimum (with actual score 5)	YES	READ DANGER USB INIT ERRORPATH UAF HARDWARE LINUS KPANIC 	NO	NO	checked

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

ActionableScore=5
ActionableScoreLower=4

## 1. ActionableScore

* Conservative score: **4**
* Paranoid score: **5**
* Final recommended bucket: **Actionable Moderate at minimum**

## 2. Signal breakdown

Conservative signals:

* **Firmware-mediated or external device influence: +1**
  A malicious or faulty USB MIDI 2.0 device can influence the probe and URB completion behavior.

* **Generic memory corruption, strong primitive: +2**
  The report shows a real KASAN slab-use-after-free in `input_urb_complete()` after endpoint storage and coherent URB buffers were freed.

* **Real lifetime corruption: +1**
  Submitted URBs outlive the endpoint object and complete after teardown.

* **Reliable kernel crash / strong DoS: +1**
  The observed failure is a KASAN slab-use-after-free and likely kernel crash or panic depending on config.

* **Privileged kernel/device-management memory corruption path: +1**
  The bug is in USB driver endpoint and URB lifetime management, a trusted kernel device path.

Negative signals:

* **Physical-only or rare hardware-only condition: -2**
  Normal exploitation requires physical USB access or an equivalent USB device emulation path.

* **Hard or unreliable race / special timing required: -1**
  The bug depends on probe error ordering versus outstanding URB completion timing.

Paranoid additional signal:

* **Weak LPE concern: +1**
  This is a real UAF in an asynchronous completion path, and the stale endpoint can be dereferenced or used for resubmission. There is no demonstrated reclaim or controlled overwrite, so this is only a weak LPE concern.

## 3. Reachability analysis

The realistic attacker is someone who can present a malicious or faulty USB MIDI 2.0 device to the system. No local software privilege is required in the physical attack model, but the attacker needs physical USB access or an equivalent local USB emulation mechanism. The path is not network reachable in the normal model.

Namespaces and containers do not significantly lower the requirement, because the trigger is device probe and USB HCD completion behavior rather than an ordinary namespaced syscall interface. The affected driver is in a common USB audio subsystem, but MIDI 2.0 endpoint creation is more specific than generic USB audio playback or capture.

## 4. Severity interpretation

This is stronger than an ordinary Moderate crash bug because it is a confirmed kernel UAF in an async completion path. Realistic impact is most likely denial of service through a crash during device probe or teardown. Theoretical memory corruption potential exists because freed endpoint state is accessed from completion context, but the patch and report do not show attacker-controlled reclaim, arbitrary write, type confusion, or a reliable privilege escalation primitive.

Therefore the conservative handling is borderline manual review, while the paranoid handling is Actionable Moderate and should not be auto-closed.

## 5. One-sentence report phrase

A malicious or faulty USB MIDI 2.0 device can trigger a probe error path where submitted input URBs complete after endpoint storage has been freed, causing a slab use-after-free in `input_urb_complete()` and likely kernel crash, with only weak theoretical privilege-escalation concern.

## 6. Manual review recommendation

**MANUAL CHECK REQUIRED**

Reason: confirmed UAF in kernel USB completion context, physical attack surface, and possible but unproven escalation potential.

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

Patch: ALSA: usb-audio: Kill MIDI 2.0 URBs before freeing endpoints [ Upstream
Commit: bcdd5a7363bdd287253c406a9c0205f5722058e7
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=bcdd5a7363bdd287253c406a9c0205f5722058e7

Changed files:
  sound/usb/midi2.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=bcdd5a7363bdd287253c406a9c0205f5722058e7

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

The original Linux kernel CVE announcement for CVE-2026-72443 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72443

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: 4
  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: YES
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).