* [CVE-2026-97929][MODERATE REGULAR] ALSA: usbusx2y: validate URB actual_length in interrupt callback
@ 2026-09-25 12:01 21% AL-KERNEL
0 siblings, 0 replies; 1+ results
From: AL-KERNEL @ 2026-09-25 12:01 UTC (permalink / raw)
To: kernel-cve
CVE: CVE-2026-97929
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: ALSA: usbusx2y: validate URB actual_length in interrupt callback
Commit: c156584999bf15118f523ef6c6fedc5b21f46bd9
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=c156584999bf15118f523ef6c6fedc5b21f46bd9
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-97929
Analysis date: Fri, 25 Sep 2026 08:01:39 -0400
ActionableScore: 2
ActionableScore lower bound: unknown
Actionable bucket: Ordinary Moderate
Manual review required: NO
Summary:
No one-sentence report phrase was found.
======================================================================
ABOUT THIS REPORT
======================================================================
The original Linux kernel CVE announcement for CVE-2026-97929 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-97929
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 REGULAR
Manual review required: NO
A detailed explanation of the methodology and priority rules is included
at the end of this message.
======================================================================
AL-KERNEL CLASSIFICATION RESULT
======================================================================
CVE-2026-97929 MODERATE https://www.kernelcve.org/list/?q=CVE-2026-97929 CHECK WITH IMPACT FROM ORIG NN MODERATE 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:N/A:N';*CWE-457;CWE-908;*CWE-200;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:N/A:N';BEST CVSS score: '4.7';DESCR 'The ALSA usbusx2y interrupt callback processes a fixed size input buffer without first verifying that the USB interrupt transfer returned USX2Y_IN04_SIZE bytes. A short transfer can therefore leave part of the kmalloc allocated buffer uninitialized while the callback continues to process it and copies derived data into the mmap accessible ctl_snapshot array. A local process with access to the affected ALSA device and its mapped control interface may read residual kernel heap data. For the CVSS the PR:L value is used because exploitation requires a local user or process that can access the ALSA mmap interface, even when the short transfer is produced by a controlled or malfunctioning USB device. The issue is not directly network reachable and requires the affected usbusx2y hardware or an equivalent controllable USB setup. Impact is an information disclosure with no supported integrity or availability impact. Repeated short transfers could potentially expose sensitive heap remnants, so manual review of the practical disclosure scope and device access policy is appropriate.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 2) SKIP CVE-2026-97929 UNKNOWN SKIP The Fixes patch not applied yet, so unlikely that actual: url YES NO NO unknown MAYBE READ USB SIMPLEFIX HARDWARE LINUS - - checked
======================================================================
ACTIONABLESCORE ANALYSIS
======================================================================
ActionableScore=2
PrimitiveClass=CLASS_C
RealUAF=NO
HostAdminRequired=NO
NamespaceScopedPrivilege=NO
ImportantCandidate=NO
ManualReview=RECOMMENDED
AutoDowngradeAllowed=YES
1. ActionableScore
* Raw conservative score: 2
* Conservative score: 2
* Raw paranoid score: 2
* Paranoid score: 2
* No floor or cap was applied.
* Final recommended bucket: **Ordinary Moderate**::
2. Signal breakdown
Positive signals:
* +1 Firmware-mediated external influence. A short transfer produced by the USB device reaches the vulnerable interrupt callback.
* +1 Local unprivileged trigger. A local process with permission to use the ALSA mmap control interface can read `ctl_snapshot` without host-admin-equivalent privilege.
* +1 Practical exploit chain. The established chain is short USB transfer, processing of the uninitialized buffer tail, copying into `ctl_snapshot`, and local mmap readback.
* +1 Confidentiality plausible. Residual kernel heap data is copied into a userspace-accessible mapping.
Negative signals:
* -2 Physical-only or rare hardware-dependent path. Exploitation requires an affected usbusx2y USB device or an equivalent controllable USB setup capable of producing short interrupt transfers.
Important non-awarded signals:
* No UAF, OOB write, post-free access, refcount mutation, or active-object lifetime violation is established.
* No controlled kernel write, controlled reclaim, integrity impact, privilege escalation, or availability impact is demonstrated.
* Remote network reachability is not established.
* No additional point is awarded for repeated leakage because repetition does not create a distinct primitive.
* Memory-layout-invariant scoring is not added separately because the `actual_length` mismatch is the same fact already underlying the disclosure chain.
* The paranoid score is not increased to model unspecified sensitive data. The amount and security value of leaked heap remnants remain unresolved.
3. Reachability analysis
The complete attack model requires a local process that can mmap the affected ALSA control interface and a compatible USB device that returns a short interrupt transfer. This can be below host-admin privilege where audio-device access is granted to an ordinary desktop or audio-group user.
The operation is not namespace-capability based, and an attacker-created user or network namespace does not provide access to the USB or ALSA device. No sysctl or boot-time prerequisite is identified, but the relevant driver and hardware must be present. There is no race. The trigger depends on device behavior rather than timing.
A malfunctioning device can cause accidental disclosure. Deliberate exploitation additionally requires control over, or reliable influence on, the USB transfer behavior and access to the resulting mmap data.
4. Primitive and severity interpretation
The exact primitive is processing of uninitialized bytes in the unwritten tail of a fixed-size `kmalloc` buffer, followed by transfer of resulting data into a userspace-accessible snapshot array. This is fixed buffer storage, not an active structured-object UAF.
The demonstrated consequence is a limited local kernel heap information disclosure. The practical scope depends on how much of the uninitialized tail reaches `ctl_snapshot`, whether values are transformed before copying, and what heap contents occupy the allocation.
Theoretical disclosure of sensitive heap remnants is possible, but there is no evidence of substantial arbitrary kernel disclosure, memory corruption, integrity impact, LPE, or host crash. The issue is therefore CLASS_C rather than an Important-preserving CLASS_A primitive.
ImportantCandidate is NO because the established primitive is a hardware-dependent, bounded disclosure with no broader exploitation mechanism. AutoDowngradeAllowed is YES because no unresolved corruption, lifetime, ownership, or authorization-boundary primitive remains. Manual review is still recommended to confirm the exact number and form of exposed bytes.
5. One-sentence report phrase
A short USB interrupt transfer can cause the ALSA usbusx2y callback to copy residual kernel heap data into a locally mmap accessible control snapshot, resulting in a hardware-dependent information disclosure.
6. Manual review recommendation
MANUAL CHECK RECOMMENDED
Confirm the exact bytes copied into `ctl_snapshot`, any transformation applied to them, ALSA device permissions, and whether a programmable USB device can trigger repeatable disclosure.
7. Call-site confidence
Call-site confidence: high
======================================================================
UPSTREAM PATCH SUMMARY
======================================================================
Patch: ALSA: usbusx2y: validate URB actual_length in interrupt callback
Commit: c156584999bf15118f523ef6c6fedc5b21f46bd9
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=c156584999bf15118f523ef6c6fedc5b21f46bd9
Commit description:
i_usx2y_in04_int() processes the interrupt URB data without checking
urb->actual_length. A short transfer from a malfunctioning device
would cause the handler to process uninitialized heap data from the
kmalloc-allocated in04_buf, which is then copied to the mmap-accessible
ctl_snapshot[] array.
Fix by using kzalloc() for in04_buf to zero-initialize the buffer,
and adding an actual_length check to skip processing on short
transfers while still resubmitting the URB.
Fixes: 1da177e ("Linux-2.6.12-rc2")
Cc: [email protected]
Signed-off-by: Tristan Madani <[email protected]>
Link: https://patch.msgid.link/[email protected]
Signed-off-by: Takashi Iwai <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>
Changed files:
sound/usb/usx2y/usbusx2y.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=c156584999bf15118f523ef6c6fedc5b21f46bd9
======================================================================
DETAILED REPORT METHODOLOGY
======================================================================
The original Linux kernel CVE announcement for CVE-2026-97929 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-97929
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:L/I:N/A:N
The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:N/A:N
The Best / paranoid CVSS score: 4.7
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: unknown
Paranoid ActionableScore: 2
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 REGULAR
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 [email protected] (and both
send reply to CVE record itself too and see "reply" button below for howto reply).
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