[CVE-2026-46090][MODERATE 7.0] ALSA: aloop: Fix peer runtime UAF during format-change stop [ Upstream

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

CVE: CVE-2026-46090
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: ALSA: aloop: Fix peer runtime UAF during format-change stop [ Upstream
Commit: 03f52a9c170431e8f10e156b9dc0dae80b3e9198
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=03f52a9c170431e8f10e156b9dc0dae80b3e9198
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-46090
Analysis date: Fri, 26 Jun 2026 14:43:13 -0400
ActionableScore: 5
ActionableScore lower bound: 4
Actionable bucket: Actionable Moderate at minimum
Manual review required: YES

Summary:
A race in ALSA snd-aloop can leave the playback trigger path holding a stale peer substream pointer while a concurrent close detaches or frees the peer runtime, causing a local kernel UAF that is at least a DoS and should be manually reviewed for LPE potential.

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ABOUT THIS REPORT
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The original Linux kernel CVE announcement for CVE-2026-46090 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-46090

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-2026-46090	MODERATE	CHECK	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-667;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '7';DESCR 'ALSA aloop has a race where loopback_check_format can decide to stop a running peer capture stream after dropping cable lock while a concurrent close can clear cable streams and detach or free the peer runtime. This can leave the playback trigger path with a stale peer substream pointer and create a use-after-free condition in the local kernel audio path. For the CVSS the PR:L is used because a local user or service with access to ALSA loopback PCM devices can potentially trigger the bug without full administrator privileges. The issue is not network reachable and requires local interaction with the snd-aloop PCM device. Impact is at least a local denial of service via kernel crash and in worst case may allow privilege escalation because the primitive is a kernel use-after-free race. For the paranoid score, choose the highest still-defensible interpretation supported by the bug class and patch context, with preference for manual-review sensitivity over autoclosed false negatives.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate at minimum (with actual score 5)	YES	LOCK INIT UAF HARDWARE LINUS SYZBOT KPANIC 	NO	NO	guess

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ACTIONABLESCORE ANALYSIS
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ActionableScore=5
ActionableScoreLower=4

## 1. ActionableScore

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

## 2. Signal breakdown

Triggered signals:

* Local unprivileged trigger: +1
  A local user or local service with access to ALSA loopback PCM devices can plausibly trigger playback/capture open, format change, stop, and close paths.

* Memory corruption, weak/indirect corruption candidate: +1
  The patch and commit explicitly describe a stale peer substream pointer and peer runtime UAF. However, this is a race-only UAF without shown reclaim, overwrite, callback dispatch, type confusion, or refcount takeover, so the race-UAF downgrade rule applies.

* Real lifetime corruption: +1
  The bug is a concrete lifetime mismatch: snd_pcm_stop() runs after dropping cable->lock while concurrent close can detach or free the peer runtime.

* Reliable kernel crash / strong DoS: +1
  A stale runtime/substream pointer in ALSA PCM stop handling is a credible kernel crash path, and the bug was reported by syzbot.

* Hard or timing-dependent race: -1 for conservative score
  Triggering requires a race between format-change stop and concurrent close. For paranoid scoring, this penalty is relaxed because syzbot coverage implies the race is practically reachable under stress.

* Broad/local subsystem exposure: +1 for paranoid score
  ALSA device nodes are common local interfaces. snd-aloop itself is not always loaded by default, but once available it is reachable through ordinary local PCM operations.

Not awarded:

* No remote/network trigger.
* No strong LPE bonus.
* No confidentiality or integrity bonus in the conservative score.
* No high-control API bonus, because ALSA object configuration alone does not demonstrate allocator control, callback control, or controlled reclaim.

## 3. Reachability analysis

The bug is local-only and requires interaction with the ALSA snd-aloop PCM device. A realistic trigger requires one side changing playback parameters so loopback_check_format() stops a running capture peer, while another thread closes the peer stream and frees or detaches its runtime. This is not network reachable.

Privileges depend on device-node permissions. On many systems, /dev/snd access is granted to local desktop users, audio group members, or service processes, so PR:L is the practical assumption. It should not be treated as PR:H unless snd-aloop is restricted to administrators only. Containers may matter if /dev/snd or snd-aloop devices are passed through to the container, but this is not a default container exposure.

snd-aloop is not necessarily loaded by default, which limits exposure compared with core ALSA paths. However, when enabled, the path is reachable via normal local audio operations.

## 4. Severity interpretation

This is stronger than an ordinary Moderate cleanup because it is an explicit kernel UAF race in a local device interface. Conservative handling should treat it as a borderline manual-review issue with local DoS as the demonstrated impact.

Theoretical privilege escalation is possible in the broad sense that kernel UAF races can sometimes become LPE, but this patch does not show attacker-controlled reclaim, write-after-free, callback hijack, type confusion, or refcount takeover. Therefore the main score should not classify it as a Strong Important candidate solely from the UAF label. The paranoid score reaches Actionable Moderate at minimum to avoid auto-closing a real lifetime-corruption bug.

## 5. One-sentence report phrase

A race in ALSA snd-aloop can leave the playback trigger path holding a stale peer substream pointer while a concurrent close detaches or frees the peer runtime, causing a local kernel UAF that is at least a DoS and should be manually reviewed for LPE potential.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

Reason: this is an explicitly described kernel UAF race with local reachability. Even though the patch does not demonstrate a strong exploitation primitive, lifetime corruption in kernel object paths should not be auto-closed.

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

Patch: ALSA: aloop: Fix peer runtime UAF during format-change stop [ Upstream
Commit: 03f52a9c170431e8f10e156b9dc0dae80b3e9198
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=03f52a9c170431e8f10e156b9dc0dae80b3e9198

Changed files:
  sound/drivers/aloop.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=03f52a9c170431e8f10e156b9dc0dae80b3e9198

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

The original Linux kernel CVE announcement for CVE-2026-46090 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-46090

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: 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).