[CVE-2026-97931][MODERATE 7.0] ALSA: us122l: Prevent write upgrades for read mappings [ Upstream

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

CVE: CVE-2026-97931
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: ALSA: us122l: Prevent write upgrades for read mappings [ Upstream
Commit: 64a87950239867682cde128020e1a47088295e5c
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=64a87950239867682cde128020e1a47088295e5c
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-97931
Analysis date: Fri, 25 Sep 2026 11:16:37 -0400
ActionableScore: 5
ActionableScore lower bound: 4
Actionable bucket: Actionable Moderate / Strong Important candidate requiring manual review
Manual review required: YES

Summary:
No one-sentence report phrase was found.

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

The original Linux kernel CVE announcement for CVE-2026-97931 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-97931

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-2026-97931	MODERATE	https://www.kernelcve.org/list/?q=CVE-2026-97931 CHECK WITH IMPACT FROM ORIG NN MODERATE	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-284;*CWE-416;*CWE-787;CWE-269;Other CVSS 'AV:L/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:H';BEST CVSS score: '7.8';DESCR 'An ALSA us122l hwdep read buffer mapping can be created with PROT_READ while retaining VM_MAYWRITE. A local process that can open the hwdep device with O_RDWR can later use mprotect() to make the mapping writable and modify struct usb_stream data including read_size. A modified read_size can cause mappings beyond the intended read allocation and can make usb_stream_free call free_pages_exact on pages outside the allocation. This creates a plausible kernel memory corruption condition with potential use after free or invalid free consequences. For the CVSS the PR:L metric reflects that the attacker needs local access to the affected hwdep device rather than full administrative privileges. The issue is not network reachable. Impact is at least local denial of service and may include confidentiality integrity and privilege escalation consequences due to the invalid page free primitive. YES REQUIRES MANUAL CHECK';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate / Strong Important candidate requiring manual review (with actual score 5)	YES	READ USB INIT SIMPLEFIX HARDWARE LINUS  KPANIC INCREASED_TO_HIGH_BASED_ON_GUESSCVSS DECREASED_TO_MODERATE7_BASED_ON_FALSEPOSCHECKOFKP	NO	NO	checked

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

ActionableScore=5
ActionableScoreLower=4
PrimitiveClass=CLASS_A
RealUAF=NO
HostAdminRequired=NO
NamespaceScopedPrivilege=NO
ImportantCandidate=YES
ManualReview=REQUIRED
AutoDowngradeAllowed=NO

1. ActionableScore

* Raw conservative score: 4
* Conservative score: 4
* Raw paranoid score: 5
* Paranoid score: 5
* Final recommended bucket: **Actionable Moderate / Strong Important candidate requiring manual review**::

Conservative arithmetic: Strong corruption primitive +2. Concrete authorization bypass +2. Local below-host-admin trigger +1. Reliable kernel crash or strong DoS +1. Rare hardware requirement -2. Total 4.

Paranoid arithmetic: Conservative 4. Plausible user-visible disclosure through access to pages beyond the intended allocation +1. Total 5.

No floor or cap was applied.

2. Signal breakdown

* +2 Strong corruption primitive. The attacker can use an initially read-only hwdep mmap mapping and later upgrade it with mprotect because VM_MAYWRITE remains set. This allows modification of usb_stream read_size, a kernel-resident allocation boundary used by both the fault handler and usb_stream_free.
* +2 Concrete authorization decision bypass. The driver explicitly rejects initially writable mappings but fails to prevent the later mprotect write upgrade. This changes an intended denied write access into an allowed writable mapping.
* +1 Local below-host-admin trigger. A process allowed to open the ALSA hwdep node O_RDWR can perform mmap and mprotect without requiring host-root privilege. Device-node access may be delegated through normal audio-device permissions.
* +1 Reliable kernel crash or strong DoS. A modified read_size can cause free_pages_exact to release pages outside the intended allocation, which can corrupt allocator state or cause a kernel fault.
* -2 Rare hardware requirement. The vulnerable path is specific to the ALSA US122L USB audio driver and requires the affected physical device and driver to be present.

Paranoid-only signal:

* +1 Plausible confidentiality impact. The commit states that modifying read_size can map and access pages beyond the allocation. Since this mapping is exposed to the local process, adjacent kernel-managed pages may become user-accessible. The exact data exposure depends on allocation layout and fault-handler behavior, so this is not counted conservatively.

Important non-awarded signals:

* No RealUAF point. The patch establishes an invalid free and potential later use-after-free consequences, but does not directly establish a stale dereference after the invalid free.
* No controlled reclaim or replacement point. The supplied context does not show controlled reuse of pages released outside the allocation.
* No arbitrary kernel write point. The attacker directly controls read_size and indirectly influences the freed range, but cannot select an arbitrary target address.
* No explicit privilege-escalation point. Privilege escalation is plausible from the invalid free primitive but is not demonstrated.
* No separate integrity point. Unauthorized mutation of kernel allocation metadata and the resulting invalid free are already counted as the strong corruption primitive.
* No additional availability point. The possible allocator corruption or crash is counted once as strong DoS.
* No remote-reachability point. This is a local hwdep device interface issue.

3. Reachability analysis

The attacker model is a local process that can open the affected ALSA hwdep device node with O_RDWR. The complete trigger consists of creating a read mapping with PROT_READ, upgrading protection with mprotect, changing the mapped usb_stream read_size field, and reaching either the read-buffer fault path or usb_stream_free.

Host-admin-equivalent privilege is not inherently required. Access to ALSA device nodes is commonly delegated to non-root users through audio-device permissions, session management, or an audio-related group. This is still an access prerequisite and may not be available to every local account.

The operation is not namespace-scoped. User namespaces or network namespaces do not provide the relevant ALSA hwdep device access or make the complete operation available.

The affected driver requires an attached and supported US122L-family USB audio device. This is a concrete hardware prerequisite and reduces broad deployment exposure, but it does not remove the seriousness of the corruption primitive on affected hosts. There is no race requirement.

4. Primitive and severity interpretation

The exact primitive is a writable upgrade of a mapping intended to expose a read-only USB stream buffer. The mapping includes the beginning of a struct usb_stream allocation, allowing the local process to alter read_size after the driver has validated the original mapping permissions.

This is not fixed stale storage and not a cleanup-only stale dereference. It is attacker-influenced active kernel metadata corruption. The modified read_size is consumed by the VMA fault handler to determine read-buffer page boundaries and by usb_stream_free to determine the range passed to free_pages_exact. The latter creates an invalid free primitive that may release kernel pages outside the original allocation.

There is no directly established use-after-free, so RealUAF is NO. However, the invalid free can create later allocator corruption, page ownership corruption, or use-after-free conditions. The patch-supported practical consequence is at least local kernel crash or corruption. Confidentiality exposure is plausible because the commit explicitly describes mapping and accessing pages beyond the allocation, but exact disclosure is not demonstrated.

The issue is CLASS_A because the attacker directly bypasses an intended write-protection boundary and controls a kernel allocation-size field that is subsequently used in an out-of-allocation free operation. Controlled reclaim, arbitrary kernel read or write, and privilege escalation are not demonstrated, so the score remains below Strong Important range. ImportantCandidate is YES because the invalid free primitive requires manual exploitation review and should not be automatically downgraded as an ordinary driver crash.

AutoDowngradeAllowed is NO because the patch establishes both a concrete permission bypass and a meaningful kernel memory-corruption primitive. The rare-device constraint reduces deployment exposure but does not make the issue safe for automatic closure.

5. One-sentence report phrase

A local process with O_RDWR access to an affected ALSA US122L hwdep device can upgrade a read-only mmap mapping with mprotect, modify usb_stream read_size, and trigger out-of-allocation page mapping or freeing that may corrupt kernel memory and cause a kernel crash.

6. Manual review recommendation

MANUAL CHECK REQUIRED

The patch establishes a direct mapping-permission bypass and an attacker-influenced invalid free outside the original allocation. Manual review should determine fault-handler mapping behavior, page-allocation layout constraints, and whether the freed range can be shaped into a practical use-after-free or controlled page-ownership corruption primitive.

7. Call-site confidence

Call-site confidence: medium

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

Patch: ALSA: us122l: Prevent write upgrades for read mappings [ Upstream
Commit: 64a87950239867682cde128020e1a47088295e5c
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=64a87950239867682cde128020e1a47088295e5c

Changed files:
  sound/usb/usx2y/us122l.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=64a87950239867682cde128020e1a47088295e5c

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

The original Linux kernel CVE announcement for CVE-2026-97931 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-97931

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:L/UI:N/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: 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).