[CVE-2026-90116][MODERATE REGULAR] ALSA: mtpav: shut down output timer before card teardown [ Upstream

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

CVE: CVE-2026-90116
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: ALSA: mtpav: shut down output timer before card teardown [ Upstream
Commit: 392c985c6b03dfdf4904c0d464f18735ca3c4df8
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=392c985c6b03dfdf4904c0d464f18735ca3c4df8
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-90116
Analysis date: Fri, 18 Sep 2026 03:20:00 -0400
ActionableScore: 3
ActionableScore lower bound: unknown
Actionable bucket: Borderline / manual review recommended
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-2026-90116 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-90116

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 REGULAR
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-2026-90116	MODERATE	https://www.kernelcve.org/list/?q=CVE-2026-90116 CHECK WITH IMPACT FROM ORIG NN MODERATE	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:H/UI:N/S:U/C:L/I:L/A:H';BEST CVSS score: '7';DESCR 'A race in the ALSA mtpav driver allows snd_mtpav_output_timer to continue using card private state while snd_mtpav_free tears that state down. The previous timer deletion does not wait for an active callback and does not prevent that callback from rearming the timer, so execution can continue against released memory and create a use after free condition. For the CVSS the PR:L value is used for the paranoid score because a local user with access to the ALSA MIDI interface may keep the output timer active while card teardown is initiated independently by device management, module removal, or hardware removal. AC:H applies because successful triggering depends on winning a narrow race between the timer callback and teardown. The issue is not network reachable. Impact is at least a local denial of service through a kernel crash and may include privilege escalation if the freed card state or embedded timer is reused in a controllable way.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline / manual review recommended (with actual score 3)  SKIP CVE-2026-90116 UNKNOWN SKIP The Fixes patch not applied yet, so unlikely that actual: url YES  NO NO unknown 	MAYBE	INIT SIMPLEFIX TIMER HARDWARE LINUS  INCREASED_TO_MODERATE7_BASED_ON_GUESSCVSS DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN4	-	-	checked

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

ActionableScore=3
PrimitiveClass=CLASS_B
RealUAF=YES
HostAdminRequired=UNKNOWN
NamespaceScopedPrivilege=NO
ImportantCandidate=NO
ManualReview=RECOMMENDED
AutoDowngradeAllowed=YES

1. ActionableScore

* Raw conservative score: 3
* Conservative score: 3
* Raw paranoid score: 3
* Paranoid score: 3
* No floor or cap was applied.
* Final recommended bucket: **Borderline / manual review recommended**::

2. Signal breakdown

* +2 Real UAF / active lifetime violation. A running timer callback can access the card-private `mtpav` state after teardown has allowed that state to be released.
* +1 Reliable kernel crash / strong DoS. Continued callback execution against released driver state, including an embedded timer, realistically supports an Oops or kernel crash.
* No race penalty. Concurrency with teardown is required, but the supplied evidence does not establish that the timing is sufficiently narrow, improbable, or difficult to repeat for the dedicated -1.
* No privilege penalty. Card teardown may require administrative device or module management, but the complete trigger privilege is not positively established by the supplied context.
* No hardware penalty. The driver is hardware-specific, but the supplied evidence does not sufficiently establish a physical-only or rare-hardware prerequisite for the vulnerable lifecycle itself.
* No structured stale-object leverage point. The callback rearms the embedded timer and accesses structured state, but attacker-controlled reclaim, replacement contents, callback selection, pointer control, or another useful post-reuse operation is not established.
* No weak or strong LPE point. Timer rearming extends the stale access but does not independently establish controlled corruption useful beyond a crash.
* No extra Availability point. Repeated callback execution and timer rearming describe the same potential crash consequence.
* No Confidentiality or Integrity points. Disclosure, directed modification, and attacker-controlled post-free data are not demonstrated.
* Controlled reclaim and arbitrary kernel read or write are not demonstrated.
* Remote reachability is not established.
* No concrete repeated release/refcount operation exists. `timer_delete()` followed by callback rearming is not a second `put`, `free`, or refcount mutation on the exact same lifetime reference.
* The dedicated repeated-release +1 was not awarded.
* Paranoid repeated-refcount leverage was not awarded.
* FLOOR 5 was not applied because this is a fixed driver-context asynchronous teardown UAF without demonstrated attacker-controlled reuse or a second lifetime/refcount release.

3. Reachability analysis

A user with access to the ALSA MIDI device may be able to activate or keep the output timer active. The vulnerable condition additionally requires card teardown while the callback is running. The supplied patch does not establish whether the same below-host-admin actor can initiate that teardown, so `HostAdminRequired` remains `UNKNOWN`.

ALSA card teardown and this physical device state are not user-namespace or network-namespace operations, so the complete trigger is not namespace scoped. No network trigger is present. The path depends on the `mtpav` driver and associated device configuration, but the available context is insufficient for a formal rare-hardware penalty.

The race involves callback execution concurrent with teardown. It may be encouraged by keeping the timer active, but direct attacker control over both sides of the race is not established.

4. Primitive and severity interpretation

The exact primitive is asynchronous post-teardown use of card-private driver state. The callback can also rearm an embedded timer after ordinary timer deletion has returned. This is a real Class B lifetime violation.

The affected storage is a fixed driver context rather than a demonstrated attacker-controlled replacement object. The stale use occurs specifically during card teardown. It is stronger than a plain invalid pointer because continued timer activity is possible, but no useful reclaim, callback hijack, disclosure, directed write, or repeated release primitive is established.

This is category A in the cleanup distinction: an asynchronous stale-object access associated with teardown. It is not category B repeated lifetime corruption because there is no concrete second free, put, release, or refcount decrement.

The demonstrated practical consequence is denial of service through a kernel fault. Privilege escalation remains theoretical and unsupported by a concrete exploitation mechanism. Therefore `ImportantCandidate=NO`. Automatic downgrade is allowed because this is presently a constrained crash-oriented Class B UAF, although manual review remains recommended to confirm teardown reachability and inspect the complete callback operations.

Likely operational severity is Moderate.

5. One-sentence report phrase

A race between the ALSA mtpav output timer and card teardown can leave a callback accessing and rearming a timer in released card-private state, creating a local use-after-free with kernel crash potential but no demonstrated controlled exploitation primitive.

6. Manual review recommendation

MANUAL CHECK RECOMMENDED

Confirm who can initiate complete card teardown and inspect all fields consumed or modified by `snd_mtpav_output_timer()` before treating the issue as definitively crash-only.

7. Call-site confidence

Call-site confidence: medium

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

Patch: ALSA: mtpav: shut down output timer before card teardown [ Upstream
Commit: 392c985c6b03dfdf4904c0d464f18735ca3c4df8
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=392c985c6b03dfdf4904c0d464f18735ca3c4df8

Changed files:
  sound/drivers/mtpav.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=392c985c6b03dfdf4904c0d464f18735ca3c4df8

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

The original Linux kernel CVE announcement for CVE-2026-90116 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-90116

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:H/UI:N/S:U/C:L/I:L/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: unknown
  Paranoid ActionableScore: 3

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 REGULAR

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).