[CVE-2026-90198][MODERATE REGULAR] ALSA: core: Fix use-after-free in snd_card_do_free() [ Upstream

[CVE-2026-90198][MODERATE REGULAR] ALSA: core: Fix use-after-free in snd_card_do_free() [ Upstream

[AL-KERNEL]

CVE: CVE-2026-90198
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: ALSA: core: Fix use-after-free in snd_card_do_free() [ Upstream
Commit: d3d67f680dbc23a5e5e3d3ecfdbf700465809877
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=d3d67f680dbc23a5e5e3d3ecfdbf700465809877
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-90198
Analysis date: Thu, 17 Sep 2026 21:47:07 -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.

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

The original Linux kernel CVE announcement for CVE-2026-90198 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-90198

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-2026-90198	MODERATE	https://www.kernelcve.org/list/?q=CVE-2026-90198 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:N/I:N/A:H';BEST CVSS score: '7';DESCR 'A use after free in ALSA snd_card_do_free can occur when a managed sound card is unbound while a userspace process still holds an open sound device file descriptor. The unbind path can wait for release_completion while the userspace close path drops the final reference and enters snd_card_do_free. After complete(card release_completion) wakes the unbind path, devres may free the memory containing struct snd_card while the close path continues and reads card managed from the freed object. For the CVSS the PR:L is used in the paranoid score because a local user with access to sound device files may be able to participate in the trigger when device lifetime is influenced by hotplug, delegated device management, or similar local mechanisms. The issue is not network reachable. Impact is at least local denial of service via kernel crash and in worst case may allow confidentiality or integrity impact due to kernel use after free memory corruption.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline / manual review recommended (with actual score 4)	YES	READ DANGER UAF HARDWARE LINUS SYZBOT  DECREASED_TO_MODERATEREG_BASED_ON_FALSEPOSCHECKOFKP	NO	NO	checked

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

ActionableScore=4
PrimitiveClass=CLASS_B
RealUAF=YES
HostAdminRequired=UNKNOWN
NamespaceScopedPrivilege=NO
ImportantCandidate=NO
ManualReview=RECOMMENDED
AutoDowngradeAllowed=YES

1. ActionableScore

* Raw conservative score: 3
* Conservative score: 4
* Raw paranoid score: 3
* Paranoid score: 4
* Applied conservative floor/cap: Real UAF floor 4 applied, 3 -> 4
* Applied paranoid floor/cap: Real UAF floor 4 applied, 3 -> 4
* Final recommended bucket: **Borderline / manual review recommended**::

2. Signal breakdown

* +2 Real UAF / lifetime violation: `struct snd_card` can be freed by the devres/unbind path after `complete(card->release_completion)`, while the close/release path continues and reads `card->managed`.
* +1 Reliable kernel crash / strong DoS: KASAN reports a use-after-free in `snd_card_do_free()` / `release_card_device()`, and the stale read is in kernel teardown context.
* +0 Local unprivileged trigger: a normal userspace process can hold and close a sound device fd, but the complete trigger also needs device unbind/lifetime teardown, and below-host-admin control of that stage is not established.
* +0 Concrete repeated release/refcount: not awarded. The visible stale operation is a read of `card->managed`. A later `kfree(card)` is control-flow dependent on the stale byte and is not established as a concrete deterministic second lifetime mutation.
* +0 Structured stale-object leverage: not awarded. `struct snd_card` is an active structured object, but the demonstrated stale use is cleanup/destructor-local and only reads a boolean after completion.
* +0 Weak LPE: not awarded separately because there is no demonstrated controlled reclaim, attacker-shaped replacement object, callback consumption, arbitrary write, or security-boundary bypass.
* +0 Confidentiality/Integrity: not awarded. C/I impact is possible only as a speculative UAF exploitation consequence, not as an established primitive.
* +0 Extra availability: not awarded because the same KASAN/Oops crash is already counted once.
* 0 negative race/timing penalty: not applied. The sequence is ordered once unbind waits for the open fd and the user closes it, rather than a narrow externally uncontrollable race.
* 0 host-admin penalty: not applied because host-admin-equivalent reachability for the complete trigger is not positively established from the supplied evidence.
* Important double-release check: first lifetime end is established via devres freeing after completion. Exact same reference survives in `snd_card_do_free()`. Second concrete lifetime/refcount mutation is not established. Dedicated +1 is withheld. FLOOR 5 is not applied.

3. Reachability analysis

The local userspace role is clear for holding an open ALSA device file descriptor and later closing it. The other required stage is unbinding or otherwise tearing down a managed sound card while that fd remains open. Normal sysfs driver unbind is host-admin controlled, but the supplied input does not fully resolve whether equivalent teardown can be attacker-induced through hotplug, delegated device management, test drivers, or another below-host-admin path.

Therefore `HostAdminRequired=UNKNOWN`, not YES and not NO. Namespace-scoped privilege is not supported by the supplied facts, so `NamespaceScopedPrivilege=NO`. No network path is involved. No special rare hardware requirement is established beyond an ALSA managed card path. The vulnerable ordering is reasonably reproducible once the teardown and open-fd condition exist, so no hard-race penalty is used.

4. Primitive and severity interpretation

The exact primitive is a real post-lifetime read from `struct snd_card` after the unbind/devres path may already have freed the memory. This is an active structured kernel object, but the demonstrated stale operation is cleanup/destructor-only and reads a single boolean field. The observed consequence is a KASAN use-after-free and likely local kernel crash/DoS.

This is CLASS_B because a real kernel lifetime violation is established. It is not CLASS_A because there is no controlled reclaim, no attacker-shaped replacement object, no arbitrary or directed write, no callback or ops pointer consumption, no disclosure path, and no demonstrated privilege escalation. It is not reduced to CLASS_C because the bug is an actual UAF, not merely an invalid state or NULL dereference.

ImportantCandidate=NO because the established primitive is constrained and crash-oriented, and meaningful exploitation leverage beyond the stale cleanup read is not established. AutoDowngradeAllowed=YES because this looks like a constrained cleanup/destructor UAF with no concrete repeated lifetime mutation and no demonstrated security-boundary primitive. Manual review is still recommended because it is a real kernel UAF and reachability of the unbind stage is not fully resolved.

5. One-sentence report phrase

A constrained ALSA managed-card teardown UAF can occur when device unbind races with a userspace file close, causing `snd_card_do_free()` to read `card->managed` after devres may have freed `struct snd_card`, with demonstrated impact of local kernel crash or DoS.

6. Manual review recommendation

MANUAL CHECK RECOMMENDED

Reason: real kernel UAF is established, but current evidence supports a constrained cleanup/destructor stale read and DoS rather than a concrete privilege-escalation primitive.

7. Call-site confidence

Call-site confidence: high

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

Patch: ALSA: core: Fix use-after-free in snd_card_do_free() [ Upstream
Commit: d3d67f680dbc23a5e5e3d3ecfdbf700465809877
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=d3d67f680dbc23a5e5e3d3ecfdbf700465809877

Changed files:
  sound/core/init.c:153

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=d3d67f680dbc23a5e5e3d3ecfdbf700465809877

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

The original Linux kernel CVE announcement for CVE-2026-90198 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-90198

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: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).