[CVE-2026-43279][MODERATE 7.0] ALSA: usb-audio: Add sanity check for OOB writes at silencing [ Upstream

[CVE-2026-43279][MODERATE 7.0] ALSA: usb-audio: Add sanity check for OOB writes at silencing [ Upstream

[AL-KERNEL]

CVE: CVE-2026-43279
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: ALSA: usb-audio: Add sanity check for OOB writes at silencing [ Upstream
Commit: fa01973bb79d70c4736b6a4b2de99fbb2cbc8d1f
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=fa01973bb79d70c4736b6a4b2de99fbb2cbc8d1f
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-43279
Analysis date: Wed, 03 Jun 2026 16:00:09 -0400
ActionableScore: 6
ActionableScore lower bound: 3
Actionable bucket: Strong Important candidate / Actionable Moderate at minimum
Manual review required: YES

Summary:
An OOB write in ALSA USB audio silent URB preparation can be triggered by an inconsistent USB audio implicit feedback setup, causing at least a kernel crash and requiring manual review because the kernel memory overwrite may have impact beyond DoS.

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

The original Linux kernel CVE announcement for CVE-2026-43279 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-43279

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-2026-43279	MODERATE	CHECK	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H';*CWE-787;*CWE-20;CWE-119;Other CVSS 'AV:P/AC:L/PR:N/UI:R/S:U/C:L/I:L/A:H';BEST CVSS score: '7.8';DESCR 'An OOB write can occur in the ALSA USB audio playback path because prepare_silent_urb can copy packet length data and silence bytes into the URB transfer buffer without first proving that the computed packet layout fits ctx buffer_size. A malicious or inconsistent USB audio device configuration can make the capture side packet sizing differ from the playback side, especially in implicit feedback mode, and this can corrupt kernel memory during silent URB preparation before real playback data is available. The most direct impact is a kernel crash or Oops. In worst case the OOB write primitive may allow confidentiality or integrity impact and should not be treated as a simple DoS only bug without manual review. For the CVSS the PR:L is used in the paranoid score because a local user who can access an already attached affected USB audio device may be able to trigger playback URB preparation without administrator privileges. The issue is not network reachable and practical exploitation usually requires physical access to a crafted USB audio device or local access to a system where such a device is already present.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 5)	YES	WRITE OOB DANGER USB KERNEL_PANIC_PLUS_UAF HARDWARE LINUS KPANIC PACKET  KPANIC DECREASED_TO_MODERATE70_BASED_ON_ACTIONABLESCORELOWERTHAN7	NO	NO	checked

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

ActionableScore=6
ActionableScoreLower=3

## 1. ActionableScore

* Conservative score: 3
* Paranoid score: 6
* Final recommended bucket: **Strong Important candidate / Actionable Moderate at minimum**::

## 2. Signal breakdown

Conservative signals:

* Firmware-mediated external influence: +1. The malformed or inconsistent USB audio device setup can influence packet sizing and URB preparation.
* Local unprivileged trigger: +1. If the affected USB audio device is already attached and accessible, a local user may be able to initiate playback without admin privileges.
* Constrained kernel buffer overwrite: +1. The bug is an OOB write into a URB transfer buffer, but the written data is mostly packet length metadata and silence bytes, not clearly attacker-chosen arbitrary payload.
* Reliable kernel crash / strong DoS: +1. The commit explicitly says the overflow can result in a crash and the fix covers a kernel Oops.
* Physical-only or rare hardware-only condition: -2. Realistic triggering generally requires a crafted or inconsistent USB audio device and implicit feedback playback conditions.
* Broad/common subsystem: +1. USB audio is a common Linux desktop and workstation subsystem, although this specific implicit feedback path is narrower.

Paranoid additional interpretation:

* Generic memory corruption: +2 instead of only constrained overwrite. The patch prevents OOB writes in kernel memory, and OOB writes require manual review even if payload and target control are unclear.
* Weak LPE concern: +1. Privilege escalation is not demonstrated, but kernel OOB write bugs can sometimes be exploitable beyond DoS depending on adjacent objects and allocator layout.
* Confidentiality impact plausible: +1. Only in the paranoid interpretation, due to possible corruption side effects from kernel memory overwrite.
* Integrity impact plausible: +1. Only in the paranoid interpretation, because OOB write may corrupt adjacent kernel state.
* Availability impact realistic: +1 is effectively covered by the strong DoS signal, so it is not double-counted separately in the conservative score.

## 3. Reachability analysis

The bug is not network reachable. The most realistic trigger is a local system with an affected USB audio device configuration, especially involving implicit feedback mode where capture-side packet sizing differs from playback-side assumptions.

A local user may be able to trigger the vulnerable path by starting playback if the device is already present and accessible through normal audio permissions. Physical access or control over the USB device strongly improves attacker control, so the conservative view treats this as hardware-mediated and partially physical. Namespaces and containers usually do not matter unless audio device nodes are passed through into the container.

The path is not an admin-only ioctl or CAP_SYS_ADMIN path in the usual playback case, but practical exploitability depends on device availability and audio permissions.

## 4. Severity interpretation

This is more than an ordinary Moderate because the patch fixes an explicit kernel OOB write. The realistic demonstrated impact is kernel Oops or crash, and the overwrite appears constrained because the data copied is packet length metadata plus silence bytes rather than an arbitrary attacker-controlled payload.

The paranoid interpretation is Actionable Moderate because OOB writes in kernel memory can sometimes become privilege escalation primitives after allocator and object-layout analysis. However, the patch does not demonstrate arbitrary write, UAF reclaim, function pointer corruption, or a reliable privilege escalation path, so it should not be treated as a clear High/Critical issue from the patch alone.

## 5. One-sentence report phrase

An OOB write in ALSA USB audio silent URB preparation can be triggered by an inconsistent USB audio implicit feedback setup, causing at least a kernel crash and requiring manual review because the kernel memory overwrite may have impact beyond DoS.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

Reason: this is a concrete kernel OOB write, not just a warning or validation cleanup. The most likely impact is DoS, but the memory corruption class and local user trigger through an already attached device make it unsafe to auto-close without reviewing overwrite bounds, payload control, adjacent allocations, and realistic device access.

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

Patch: ALSA: usb-audio: Add sanity check for OOB writes at silencing [ Upstream
Commit: fa01973bb79d70c4736b6a4b2de99fbb2cbc8d1f
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=fa01973bb79d70c4736b6a4b2de99fbb2cbc8d1f

Changed files:
  sound/usb/endpoint.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=fa01973bb79d70c4736b6a4b2de99fbb2cbc8d1f

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

The original Linux kernel CVE announcement for CVE-2026-43279 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-43279

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:L/PR:N/UI:R/S:U/C:L/I:L/A:H
  The Best / paranoid CVSS vector: AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
  The Best / paranoid CVSS score: 7.8

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: 3
  Paranoid ActionableScore: 6

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).