[CVE-2026-74497][MODERATE 7.0] ALSA: usb-audio: Clamp frame size in implicit-feedback mode

[CVE-2026-74497][MODERATE 7.0] ALSA: usb-audio: Clamp frame size in implicit-feedback mode

[AL-KERNEL]

CVE: CVE-2026-74497
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: ALSA: usb-audio: Clamp frame size in implicit-feedback mode
Commit: 56ac3e7c90f6b45969c3fd07a98fad760ffd6901
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=56ac3e7c90f6b45969c3fd07a98fad760ffd6901
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74497
Analysis date: Sat, 15 Aug 2026 18:38:24 -0400
ActionableScore: 5
ActionableScore lower bound: 3
Actionable bucket: Actionable Moderate at minimum
Manual review required: NO

Summary:
A malicious USB audio device can send an oversized implicit feedback sync packet that causes ALSA usb-audio to queue playback packet sizes above the endpoint frame limit, leading to at least denial of service and a constrained memory-safety concern.

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

The original Linux kernel CVE announcement for CVE-2026-74497 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74497

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: NO

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-2026-74497	MODERATE	CHECK WITH IMPACT FROM ORIG NN LOW	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:P/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:H';CWE-1284;*CWE-20;*CWE-787;Other CVSS 'AV:P/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '5.7';DESCR 'An oversized implicit feedback sync packet from a connected USB audio device can make snd_usb_handle_sync_urb() calculate a frame count larger than ep maxframesize. That unbounded frame count is stored in out_packet packet_size and can later enter the playback endpoint queue, potentially causing transfers beyond the endpoint hardware frame limit. For the CVSS the PR:N because the attacker only needs control of a connected USB audio device and does not need a local user account on the victim system. The issue is not network reachable and requires physical or device level access. Impact is at least denial of service through broken USB audio transfer handling or a kernel fault. For the paranoid score, limited confidentiality or integrity impact is kept because the bug is an unchecked size propagation into transfer sizing logic, but the patch does not prove a reliable privilege escalation primitive.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate at minimum (with actual score 4)	YES	USB SIMPLEFIX HARDWARE LINUS PACKET  INCREASED_FROM_LOW_BASED_ON_REQUIREMANUALCHECK DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5	NO	NO	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=5
ActionableScoreLower=3

## 1. ActionableScore

* Conservative score: 3
* Paranoid score: 5
* Final recommended bucket: **Actionable Moderate at minimum**::

## 2. Signal breakdown

Conservative signals:

* Firmware/device-mediated external influence: +1. A connected USB audio device controls the implicit feedback sync packet length.
* Reliable kernel crash / strong DoS: +1. The unbounded frame count can enter playback endpoint queueing and may drive transfers beyond endpoint limits.
* Broad/common subsystem exposure: +1. USB audio is a common desktop and workstation subsystem.
* Physical-only or device-only condition: -2. The attacker needs a malicious or compromised USB audio device, not network access.
* Availability impact realistic: +1. A malformed device can plausibly break audio transfer handling or trigger a kernel fault.

Paranoid additional signals:

* Constrained kernel transfer/buffer sizing corruption candidate: +1. The bug propagates an unchecked device-controlled size into transfer sizing logic, but no arbitrary target or payload is shown.
* Privileged kernel/device-management path: +1. The affected path is kernel USB audio endpoint handling, close to device transfer management.
* Confidentiality impact plausible: +1. Only for paranoid scoring, because oversized transfer sizing could theoretically affect adjacent kernel/device data handling.
* Integrity impact plausible: +1. Only for paranoid scoring, due to possible constrained memory safety impact, not a proven LPE primitive.
* Constrained primitive uncertainty: -1. The patch does not show attacker-controlled overwrite target, UAF, object replacement, or arbitrary write.

Net result: conservative 3, paranoid 5.

## 3. Reachability analysis

The bug can be triggered by a connected USB audio device that sends an oversized implicit feedback sync packet. No local user account is required on the victim, but the attack is not network reachable and requires physical access, malicious peripheral access, or a compromised device path. Containers and namespaces do not materially reduce the physical/device requirement. The subsystem is commonly available, but the affected path requires USB audio implicit-feedback behavior, so exposure depends on the device and active audio stream configuration.

Call-site confidence: medium. The patch shows the unchecked value being stored into `out_packet->packet_size[i]`, and the commit states that it propagates to the playback endpoint queue, but the full downstream transfer construction path is not included.

## 4. Severity interpretation

This is more than an ordinary low-risk validation fix because device-controlled packet sizing crosses into kernel playback transfer preparation. Realistically, the demonstrated impact is DoS from invalid transfer sizing or kernel fault. Theoretical memory corruption concern is limited and constrained. The patch does not demonstrate UAF, arbitrary write, attacker-controlled reclaim, callback control, or a strong privilege-escalation primitive. Therefore this is best treated as Actionable Moderate for manual triage, not a strong Important candidate by default.

## 5. One-sentence report phrase

A malicious USB audio device can send an oversized implicit feedback sync packet that causes ALSA usb-audio to queue playback packet sizes above the endpoint frame limit, leading to at least denial of service and a constrained memory-safety concern.

## 6. Manual review recommendation

MANUAL CHECK RECOMMENDED

Reason: the issue is device-reachable and involves unchecked device-controlled transfer sizing in kernel USB audio code, but the provided patch does not prove a strong memory corruption or privilege escalation primitive.

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

Patch: ALSA: usb-audio: Clamp frame size in implicit-feedback mode
Commit: 56ac3e7c90f6b45969c3fd07a98fad760ffd6901
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=56ac3e7c90f6b45969c3fd07a98fad760ffd6901

Commit description:

snd_usb_handle_sync_urb() scales received sync packet sizes by the sender's
stride and stores the result directly in out_packet->packet_size[i]. If a
connected USB device sends an oversized sync packet, this frame count can
exceed ep->maxframesize.

The un-clamped frame count then propagates to the playback endpoint queue,
potentially driving packet transfers beyond the endpoint's hardware frame
limits.

Cap the calculated frame count against ep->maxframesize in
snd_usb_handle_sync_urb() to prevent oversized packets from entering the
playback queue.

Fixes: 28acb12 ("ALSA: usb-audio: use sender stride for implicit feedback")
Cc: stable@vger.kernel.org
Assisted-by: Jetski:Gemini-3.6-Flash
Signed-off-by: Sonali Pradhan <sonalipradhan@google.com>
Link: https://patch.msgid.link/20260728202432.2354994-1-sonalipradhan@google.com
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

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=56ac3e7c90f6b45969c3fd07a98fad760ffd6901

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

The original Linux kernel CVE announcement for CVE-2026-74497 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74497

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:N/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS vector: AV:P/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:H
  The Best / paranoid CVSS score: 5.7

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: 3
  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: NO
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).