[CVE-2026-64491][MODERATE 7.0] ALSA: usx2y: us144mkii: fix work UAF on disconnect

[CVE-2026-64491][MODERATE 7.0] ALSA: usx2y: us144mkii: fix work UAF on disconnect

[AL-KERNEL]

CVE: CVE-2026-64491
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: ALSA: usx2y: us144mkii: fix work UAF on disconnect
Commit: c071df05bcda0e47aac581d4b564b2bebcb1ff60
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=c071df05bcda0e47aac581d4b564b2bebcb1ff60
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64491
Analysis date: Sat, 25 Jul 2026 09:30:03 -0400
ActionableScore: 5
ActionableScore lower bound: 2
Actionable bucket: Actionable Moderate at minimum
Manual review required: YES

Summary:
A race in the ALSA usx2y USB audio disconnect path can allow a late URB completion to rearm work after cancellation, causing the work handler to run on a freed `tascam` structure and potentially crash the kernel, with paranoid concern for UAF-based escalation requiring manual review.

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

The original Linux kernel CVE announcement for CVE-2026-64491 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64491

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-2026-64491	MODERATE	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:H/A:H';*CWE-416;CWE-362;CWE-667;Other CVSS 'AV:P/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H';Other CVSS 'AV:P/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H';BEST CVSS score: '7';DESCR 'A race in the ALSA usx2y us144mkii USB audio disconnect path can allow a late URB completion to rearm capture or MIDI work after cancel_work_sync has already run. The queued work may then execute after snd_card_free() releases the card private tascam structure, resulting in a kernel use after free. The issue is not network reachable. The practical vector is physical access to the affected USB device or control of a malicious USB device that can influence disconnect and URB completion timing. For the CVSS the PR:N because triggering through a physical USB device does not require an OS account on the victim. Impact is at least denial of service via kernel crash. In the paranoid interpretation, this UAF may also allow confidentiality or integrity impact and should be reviewed manually.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate at minimum (with actual score 4)	YES	USB INIT UAF HARDWARE LINUS  DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5	YES	NO	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=5
ActionableScoreLower=2

## 1. ActionableScore

* Conservative score: **2**
* Paranoid score: **5**
* Final recommended bucket: **Actionable Moderate at minimum**::

The conservative score is low because the realistic trigger appears to require a specific USB audio device or malicious USB-device behavior plus a narrow disconnect race. The paranoid score is higher because the bug is a real kernel workqueue UAF after `snd_card_free()`, and kernel lifetime bugs of this class should not be auto-closed without manual review.

## 2. Signal breakdown

### Conservative signals

* **Firmware-mediated external influence: +1**
  A malicious or unusual USB device can plausibly influence URB completion timing.

* **Memory corruption, weak primitive: +1**
  This is a race-dependent UAF, but the patch does not show attacker-controlled reclaim, object replacement, arbitrary write, or type confusion.

* **Real lifetime corruption: +1**
  Work can be rearmed after cancellation and later run on the freed `tascam` structure.

* **Reliable kernel crash / strong DoS: +1**
  Workqueue execution on freed driver-private memory can realistically crash the kernel.

* **Hard or unreliable race / special timing required: -1**
  The vulnerable window is between `cancel_work_sync()` and `usb_kill_anchored_urbs()`.

* **Physical-only or rare hardware/device condition: -2**
  Practical triggering requires the affected Tascam USB audio path and disconnect/URB timing control.

### Paranoid signals

* **Local or device-adjacent trigger considered: +1**
  Under a paranoid model, a local user with access to the affected USB device or a malicious USB device can influence disconnect behavior.

* **Weak LPE concern: +1**
  The stale workqueue callback runs after the object is freed. No controlled reclaim is shown, so this is not strong LPE evidence.

* **Memory corruption, weak primitive: +1**
  Race-UAF downgrade applies. Treat as weak memory corruption rather than strong exploitation primitive.

* **Real lifetime corruption: +1**
  The bug is an async completion/workqueue lifetime mismatch.

* **Reliable kernel crash / strong DoS: +1**
  Kernel UAF in a work handler is a credible DoS.

* **Hard race: -1**
  Timing-sensitive disconnect race.

* **Paranoid cap applied: 5**
  Race-UAF rule caps this class at paranoid 5 when no reclaim, overwrite, type confusion, or refcount takeover is shown.

## 3. Reachability analysis

The issue is **not network reachable**. The realistic trigger is physical or device-adjacent: disconnecting or controlling a vulnerable Tascam US-144mkII USB audio device while URBs are completing and rescheduling work.

Namespaces and containers do not materially improve reachability unless the environment passes the USB device into a container or grants device-management access. In normal deployments, this is not a broad default attack surface. The affected driver path is device-specific and requires the vulnerable USB audio hardware or a malicious USB device capable of exercising the same driver behavior.

Call-site confidence: **high**, because the patch and commit message directly show the vulnerable ordering in `tascam_disconnect()` and explain the rearm-after-cancel path.

## 4. Severity interpretation

This behaves like an **Actionable Moderate at minimum**, not a clear Strong Important candidate.

The theoretical concern is kernel UAF: a queued work item can execute after `snd_card_free()` releases the backing driver-private object. That is enough to require manual review. However, realistic exploitation evidence is limited: the trigger is physical/device-specific, timing-sensitive, and the patch does not show attacker-controlled reclaim, controlled overwrite, type confusion, or a practical privilege-escalation primitive.

## 5. One-sentence report phrase

A race in the ALSA usx2y USB audio disconnect path can allow a late URB completion to rearm work after cancellation, causing the work handler to run on a freed `tascam` structure and potentially crash the kernel, with paranoid concern for UAF-based escalation requiring manual review.

## 6. Manual review recommendation

**MANUAL CHECK REQUIRED**

Reason: this is a real kernel use-after-free in an async workqueue/URB lifetime path. Even though practical exploitation is likely limited by physical/device-specific and race-timing constraints, UAF bugs should not be auto-closed without confirming whether reclaim, stale callback effects, or attacker-influenced reuse are possible.

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

Patch: ALSA: usx2y: us144mkii: fix work UAF on disconnect
Commit: c071df05bcda0e47aac581d4b564b2bebcb1ff60
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=c071df05bcda0e47aac581d4b564b2bebcb1ff60

Commit description:

tascam_disconnect() cancels capture_work and midi_in_work before
usb_kill_anchored_urbs() kills the capture/MIDI-in URBs.  Those URBs
self-resubmit, and their completion handlers reschedule the work.

A URB that completes in the small window between cancel_work_sync() and
usb_kill_anchored_urbs() therefore re-arms the work after its only
cancel.  Nothing cancels it again before snd_card_free() frees the
card-private tascam structure, so the work handler then runs on freed
memory.

Kill the anchored URBs before cancelling the work; once the work is
cancelled no remaining URB can complete to re-arm it.

Fixes: c1bb0c1 ("ALSA: usb-audio: us144mkii: Implement audio capture and decoding")
Cc: stable@vger.kernel.org
Assisted-by: Claude:claude-opus-4-8
Signed-off-by: HyeongJun An <sammiee5311@gmail.com>
Link: https://patch.msgid.link/20260701095231.1020811-1-sammiee5311@gmail.com
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  sound/usb/usx2y/us144mkii.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=c071df05bcda0e47aac581d4b564b2bebcb1ff60

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

The original Linux kernel CVE announcement for CVE-2026-64491 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64491

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:H/PR:N/UI:N/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H
  The Best / paranoid CVSS score: 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: 2
  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).