[CVE-2026-98266][MODERATE REGULAR] ALSA: core: Fix potential UAF after asynchronous card release

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

CVE: CVE-2026-98266
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: ALSA: core: Fix potential UAF after asynchronous card release
Commit: 5c0df40aa577e405c458e44e8d458dd78407f4af
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=5c0df40aa577e405c458e44e8d458dd78407f4af
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98266
Analysis date: Sat, 10 Oct 2026 16:00:32 -0400
ActionableScore: 4
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-2026-98266 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98266

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-2026-98266	MODERATE	https://www.kernelcve.org/list/?q=CVE-2026-98266 CHECK WITH IMPACT FROM ORIG NN MODERATE | AEGIS IMPACT MODERATE_KPANIC AEGIS_AS=4 LEGACY=MODERATE RESULT=DIFF (independent Legacy and Aegis differ; FINAL: MODERATE, Aegis: MODERATE_KPANIC)	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:L/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '7';DESCR 'A race in the ALSA sound card lifecycle can leave in flight tasks accessing card dev after the underlying device has been released during asynchronous card destruction. The issue affects paths using snd_card_free_when_closed such as USB audio disconnect handling and can produce a use after free followed by a kernel crash. For the CVSS the PR:L value is used because a local user or process can access an ALSA device and keep operations in flight, although reliable triggering also depends on a concurrent device disconnect or removal event. AC:H reflects the race window between disconnect, asynchronous release, and an existing task that still uses card dev. The issue is not network reachable. Impact is at least a local denial of service via kernel crash and in the worst case may allow confidentiality, integrity, or privilege impact if the freed device memory can be reclaimed and influenced before the stale access completes. This use after free should be reviewed manually because the exact access type and reclaim control determine whether exploitation can progress beyond denial of service.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline / manual review recommended (with actual score 4)	MAYBE	UAF HARDWARE LINUS  DECREASED_TO_MODERATEREG_BASED_ON_FALSEPOSCHECKOFKP	-	-	checked

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

ActionableScore=4
PrimitiveClass=CLASS_B
RealUAF=YES
HostAdminRequired=UNKNOWN
NamespaceScopedPrivilege=NO
ImportantCandidate=NO
ManualReview=RECOMMENDED
AutoDowngradeAllowed=YES
RequiresHostUID0=UNKNOWN
AuthorizationDecisionBypass=NO
ProtectedResourceImpact=NONE
B4PendingReview=NO
B4PendingConfirmed=NO

1. ActionableScore

* Raw conservative score: 3
* Conservative score: 4
* Raw paranoid score: 3
* Paranoid score: 4
* Applied conservative REAL UAF FLOOR 4: 3 -> 4.
* Applied paranoid REAL UAF FLOOR 4: 3 -> 4.
* Final recommended bucket: **Borderline / manual review recommended**::

2. Signal breakdown

* +2 Real UAF. During asynchronous card release, the parent `card->dev` can reach the end of its lifetime while an already running task still accesses it.
* +1 Reliable kernel crash concern. Dereferencing the released `struct device` can realistically cause a kernel fault or KASAN failure.
* +0 Local unprivileged trigger. Access to ALSA device nodes may be available to a desktop or audio-session user, but the evidence does not establish that this actor can perform the complete trigger, including device disconnection.
* +0 Structured stale-object leverage. `struct device` is an active structured object, but the supplied context does not identify which stale fields are consumed or establish useful post-reuse processing.
* +0 Strong or weak LPE leverage. Controlled reclaim, attacker-shaped replacement contents, callback consumption, directed read or write, and privilege escalation are not demonstrated.
* +0 Extra availability. The same possible kernel crash is not counted twice.
* +0 Race penalty. A concurrent disconnect and in-flight operation are required, but the evidence does not establish that the timing is sufficiently narrow or uncontrollable to justify -1.
* +0 Hardware penalty. USB audio is an example of the asynchronous path, but it is common hardware and the underlying ALSA core lifetime defect is not shown to be rare-hardware-only.
* B5-R does not apply. No retry-accumulated heap OOB write exists.
* B3-PENDING does not apply. No shared-backing write is established.
* B4-PENDING does not apply. There is no authorization decision or DENY-to-ALLOW transition.

Repeated-release checks:

* The vulnerable code does not show an initial release performed through `card->dev`.
* No exact dangling reference reaches a second `put_device()` or equivalent lifetime mutation.
* The added `put_device()` balances the new `get_device()` and is not a second stale release.
* Concrete repeated release/refcount +1 was not awarded.
* Paranoid repeated-refcount leverage +1 was not awarded.
* FLOOR 5 was not applied because no repeated lifetime mutation or meaningful post-reuse processing is established.

3. Reachability analysis

A process with access to an ALSA device can potentially keep an operation in flight while asynchronous card destruction occurs. USB audio disconnection is the concrete example, but the evidence does not establish whether an ordinary user can independently initiate the complete disconnect sequence. It also does not prove that host-administrator powers are mandatory, so `HostAdminRequired` remains `UNKNOWN`.

No capability or user-namespace path is involved, and ALSA device access does not make the trigger namespace-scoped. A sound device and driver using `snd_card_free_when_closed()` must already exist. No network trigger exists. The race requires an in-flight access overlapping device disconnection, but its practical repeatability is unresolved.

4. Primitive and severity interpretation

The exact primitive is a stale post-lifetime dereference of the parent `struct device` through `card->dev`. This is an active structured-object UAF rather than a fixed stale transfer buffer. The stale use occurs in an in-flight task, not solely inside the card destructor, but the supplied call sites do not show what fields or operations are reached after the lifetime violation.

There is no concrete repeated release or refcount mutation through the dangling pointer. The patch instead introduces lifetime ownership by taking a device reference during card initialization and dropping that valid reference when the card is finally destroyed.

The issue is therefore `CLASS_B`, with kernel crash as the supported consequence. Controlled reclaim, useful object substitution, disclosure, arbitrary write, callback hijacking, and privilege escalation remain speculative. Because the demonstrated path is a constrained asynchronous UAF without identified exploitation leverage, it is not independently an Important candidate and automatic Moderate-like downgrade remains permissible after recommended human confirmation.

5. One-sentence report phrase

Asynchronous ALSA card destruction can release the parent device while an in-flight task still accesses `card->dev`, creating a local race-driven use-after-free with a realistic kernel-crash impact but no demonstrated reclaim, write, disclosure, or privilege-escalation primitive.

6. Manual review recommendation

MANUAL CHECK RECOMMENDED

Confirm the actual stale `card->dev` call sites and whether an ordinary ALSA user can reliably combine an in-flight operation with device disconnection, but current evidence does not require Important preservation.

7. Call-site confidence

Call-site confidence: medium

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

Patch: ALSA: core: Fix potential UAF after asynchronous card release
Commit: 5c0df40aa577e405c458e44e8d458dd78407f4af
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=5c0df40aa577e405c458e44e8d458dd78407f4af

Commit description:

Usually a sound driver releases the resources assigned to the card via
snd_card_free(), and it synchronizes with the whole release procedure.
However, when the card is released asynchronously via
snd_card_free_when_closed() like USB-audio driver, the situation is
slightly different; although the snd_card_disconnect() call at the
disconnection guarantees that any newer accesses will be gated, the
in-flight tasks might be still accessing to the underlying card->dev
device even after the disconnection, which would cause a
use-after-free in the end, as reported by fuzzers.

For addressing the bug above, this patch takes the refcount of
card->dev at initialization of the card object, and releases at its
destructor.   This assures the availability of the card->dev in its
whole lifecycle.

Reported-by: Farhad Alemi <farhad.alemi@berkeley.edu>
Closes: https://lore.kernel.org/CA+0ovChexj4TrZL_2iG_P0WBEbZc5+73GfB3DkciQi=R8pZOnA@mail.gmail.com
Closes: https://lore.kernel.org/CA+0ovCgQUQNN=Z1tJTouiCsDaXR5M-3-SQEGk-cpPXQkM5Xh+w@mail.gmail.com
Cc: <stable@vger.kernel.org>
Link: https://patch.msgid.link/20260912162150.455144-1-tiwai@suse.de
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  sound/core/init.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=5c0df40aa577e405c458e44e8d458dd78407f4af

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

The original Linux kernel CVE announcement for CVE-2026-98266 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98266

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:L/UI:N/S:U/C:N/I:N/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: 4

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).