[CVE-2026-64490][IMPORTANT] ALSA: virtio: Validate control metadata from the device

[CVE-2026-64490][IMPORTANT] ALSA: virtio: Validate control metadata from the device

[AL-KERNEL]

CVE: CVE-2026-64490
Priority: IMPORTANT
AL-KERNEL base severity: IMPORTANT
KPANIC flag: YES
Patch: ALSA: virtio: Validate control metadata from the device
Commit: 3243563f99ef5d3949b934bd6390a5679405d0e1
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=3243563f99ef5d3949b934bd6390a5679405d0e1
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64490
Analysis date: Sat, 25 Jul 2026 13:14:34 -0400
ActionableScore: 7
ActionableScore lower bound: 6
Actionable bucket: Strong Important candidate / Actionable Moderate at minimum
Manual review required: YES

Summary:
A malicious virtio sound device can provide invalid ALSA control type or count metadata that drives out-of-bounds access and memcpy operations in the guest kernel, causing at least guest DoS and potentially memory corruption.

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

The original Linux kernel CVE announcement for CVE-2026-64490 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64490

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: IMPORTANT
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-2026-64490	IMPORTANT	CHECK WITH IMPACT FROM ORIG NN LOW	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H';*CWE-20;CWE-129;*CWE-787;CWE-125;Other CVSS 'AV:L/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:H';BEST CVSS score: '8.4';DESCR 'ALSA virtio control handling trusted metadata returned by the virtio sound device. An invalid control type can index g_v2a_type_map out of bounds, and an oversized count can drive loops and memcpy operations beyond fixed virtio_snd_ctl_value and snd_ctl_elem_value arrays. This is a device to guest attack surface rather than a packet network issue. For the CVSS the PR:N is used because no credentials inside the target guest are required once a malicious or compromised virtio sound device is attached. Impact is at least guest kernel denial of service and in worst case may allow confidentiality or integrity impact due to out of bounds access and possible memory corruption.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 7)	YES	OOB VIRT ERRORPATH HARDWARE LINUS KPANIC  KPANIC INCREASED_TO_HIGH_BASED_ON_GUESSCVSS	YES	NO	checked

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

ActionableScore=7
ActionableScoreLower=6

## 1. ActionableScore

* Conservative score: 6
* Paranoid score: 7
* Final recommended bucket: **Strong Important candidate / Actionable Moderate at minimum**::

## 2. Signal breakdown

* Firmware-mediated external influence: +1. The metadata is supplied by a virtio sound device, so the attacker model is a buggy or malicious device or device model influencing the guest kernel.
* Generic memory corruption, strong corruption primitive: +2. The commit explicitly describes out-of-bounds access from invalid control type and oversized count, including indexing g_v2a_type_map and sizing loops or memcpy against fixed-size arrays.
* Reliable kernel crash / strong DoS: +1. OOB access in kernel ALSA control paths can realistically crash the guest kernel.
* Privileged kernel/device-management memory corruption path: +1. The corruption occurs in a trusted kernel driver path consuming device-provided metadata.
* Confidentiality impact plausible: +1. OOB reads from invalid type/count handling may expose adjacent kernel data depending on call path.
* Integrity impact plausible: +1. Oversized count used for memcpy/loops against fixed-size structures creates a plausible write-side corruption concern.
* Rare/configuration-dependent exposure: -1. The vulnerable path requires virtio-snd to be present and configured, which is common in some VM desktop environments but not a default server-wide exposure.

Paranoid score adds stronger guest-kernel compromise concern from device-controlled OOB access, raising practical triage from Actionable Moderate to Strong Important candidate.

## 3. Reachability analysis

The direct attacker is a malicious or compromised virtio sound device, hypervisor device model, or firmware-like device endpoint supplying invalid ALSA control metadata to the guest. No network reachability is shown. No credentials inside the guest are required once the malicious device is attached, but the affected guest must use virtio-snd and expose the control parsing path. Ordinary local namespaces do not materially reduce the requirement because the primary input comes from the virtio device, not from a container-local interface. Call-site confidence: high, because the commit identifies the affected functions and the patch validates metadata before ALSA controls are exposed.

## 4. Severity interpretation

This is not an ordinary Moderate validation bug. The patch context explicitly identifies OOB access and memcpy or loop sizing against fixed-size kernel structures. Realistic impact is at least guest kernel DoS, while the technically defensible worst case includes guest kernel memory corruption with confidentiality and integrity impact. The exploitability is constrained by the need for a malicious or buggy virtio-snd device, so it is not a broad remote issue, but it should not be auto-closed.

## 5. One-sentence report phrase

A malicious virtio sound device can provide invalid ALSA control type or count metadata that drives out-of-bounds access and memcpy operations in the guest kernel, causing at least guest DoS and potentially memory corruption.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED. The issue involves device-controlled metadata reaching OOB array indexing and memcpy-sized operations in kernel ALSA virtio control handling, which is enough for Important-candidate review even though the exposure is device-to-guest rather than network-facing.

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

Patch: ALSA: virtio: Validate control metadata from the device
Commit: 3243563f99ef5d3949b934bd6390a5679405d0e1
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=3243563f99ef5d3949b934bd6390a5679405d0e1

Commit description:

virtio-snd control handling trusts the device-provided control type and
value count returned by the device.

That metadata is then used directly to index g_v2a_type_map[] in
virtsnd_kctl_info(), and to size loops and memcpy() operations in
virtsnd_kctl_get() and virtsnd_kctl_put() against fixed-size
virtio_snd_ctl_value and snd_ctl_elem_value arrays.

A buggy or malicious device can therefore trigger out-of-bounds access by
advertising an invalid control type or an oversized value count.

Validate control type and count once in virtsnd_kctl_parse_cfg(), before
querying enumerated items or exposing the control to ALSA.

Fixes: d6568e3 ("ALSA: virtio: add support for audio controls")
Cc: stable@vger.kernel.org
Signed-off-by: Cássio Gabriel <cassiogabrielcontato@gmail.com>
Link: https://patch.msgid.link/20260507-alsa-virtio-validate-kctl-info-v1-1-7404fb12ec37@gmail.com
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  sound/virtio/virtio_kctl.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=3243563f99ef5d3949b934bd6390a5679405d0e1

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

The original Linux kernel CVE announcement for CVE-2026-64490 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64490

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:L/PR:N/UI:N/S:U/C:L/I:L/A:H
  The Best / paranoid CVSS vector: AV:L/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
  The Best / paranoid CVSS score: 8.4

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: 6
  Paranoid ActionableScore: 7

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: IMPORTANT
KPANIC detected for this report: YES
Published priority for this report (same as in Subject): IMPORTANT

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).