[CVE-2026-74639][MODERATE 7.0] ALSA: us144mkii: re-anchor capture URBs on resubmission

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

CVE: CVE-2026-74639
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: ALSA: us144mkii: re-anchor capture URBs on resubmission
Commit: 7779249561d14b8a17c0c83783225794e24a587d
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=7779249561d14b8a17c0c83783225794e24a587d
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74639
Analysis date: Sat, 22 Aug 2026 18:04:09 -0400
ActionableScore: 8
ActionableScore lower bound: 6
Actionable bucket: Strong Important candidate / Actionable Moderate at minimum
Manual review required: YES

Summary:
ALSA us144mkii capture URBs can remain queued after teardown because resubmitted URBs are not re anchored, allowing later USB completions to write device supplied data into freed buffers and dereference a freed driver object, causing kernel UAF and possible local DoS or privilege escalation.

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ABOUT THIS REPORT
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The original Linux kernel CVE announcement for CVE-2026-74639 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74639

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-2026-74639	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-672;CWE-362;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:H';BEST CVSS score: '7';DESCR 'ALSA us144mkii capture URBs can be resubmitted from capture_urb_complete without being re anchored, leaving tascam capture_anchor empty after the first completion. During disconnect, suspend, stream stop, or URB cleanup, usb_kill_anchored_urbs may return without waiting for still queued capture URBs. The host controller can then complete those URBs after usb_free_coherent and snd_card_free, writing device supplied capture data into freed memory and dereferencing the freed driver object. For the CVSS the PR:L is used for the paranoid score because a local user with access to the ALSA capture device or delegated USB device control may be able to start capture and coordinate teardown without full administrator privileges. The issue is not network reachable. Impact is at least local denial of service via kernel crash and in worst case may allow confidentiality or integrity impact due to use after free memory corruption.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 8)  SKIP CVE-2026-74639 UNKNOWN SKIP The Fixes patch not applied yet, so unlikely that actual: url YES  NO NO unknown 	MAYBE	READ DANGER USB UAF HARDWARE LINUS KPANIC  KPANIC INCREASED_TO_HIGH_BASED_ON_ACTIONABLESCOREHIGHEREQTHAN6 DECREASED_TO_MODERATE7_BASED_ON_FALSEPOSCHECKOFDH	-	-	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=8
ActionableScoreLower=6

## 1. ActionableScore

* Conservative score: 6
* Paranoid score: 8
* Final recommended bucket: **Strong Important candidate / Actionable Moderate at minimum**::

## 2. Signal breakdown

Triggered signals:

* Local unprivileged trigger: +1
  A local user with access to the ALSA capture device may be able to start capture and trigger stream stop or teardown paths without full root privileges.

* Firmware-mediated external influence: +1
  The completed USB URB writes device-supplied capture data into the transfer buffer. A malicious or abnormal USB device can influence the data reaching freed memory.

* Generic memory corruption, strong corruption primitive: +2
  The commit explicitly shows KASAN slab-use-after-free and a write of 512 bytes into a freed coherent buffer.

* Real lifetime corruption: +1
  This is a real async lifetime mismatch. URBs remain queued after cleanup because they are no longer anchored, then complete after buffers and the driver object are freed.

* Reliable kernel crash / strong DoS: +1
  KASAN reports use-after-free in both the transfer buffer path and capture_urb_complete. Kernel crash is realistic.

* Privilege escalation plausible, weak-to-moderate: +1 conservative / +2 paranoid
  Conservative scoring treats LPE as plausible but not demonstrated because reclaim and target selection are not shown. Paranoid scoring raises this because there is write-after-free with device-supplied data plus stale callback dereference.

* Rare hardware / device-specific exposure: -1
  The affected path is specific to the ALSA us144mkii USB audio driver and requires the relevant device or driver path.

Not counted:

* Remote reachable / network-triggerable: +0
  No network path is involved.

* Dirty-Pipe-like or page-cache ownership bypass: +0
  The primitive is USB/URB lifetime corruption, not page-cache or CoW ownership bypass.

## 3. Reachability analysis

The bug can be triggered in systems using the affected ALSA us144mkii USB audio driver. Realistic attackers include a local user with access to the ALSA capture device, a container or sandbox with delegated `/dev/snd` access, or a malicious physical USB device. Full administrator privileges are not necessarily required if audio device access is granted to non-root users.

Namespaces and containers matter because audio devices are commonly delegated into desktop sessions, containers, or service sandboxes. In those cases this should be treated closer to PR:L than PR:H.

The path is not broadly default-exposed like networking or VFS, because it requires this specific USB audio driver and active capture URBs. However, once the device path is present, the lifetime bug is concrete and not merely theoretical.

Call-site confidence: high. The commit message explicitly identifies the affected cleanup paths, the missing anchor operation, the freed objects, and KASAN-confirmed UAF writes and reads.

## 4. Severity interpretation

This is not an ordinary Moderate cleanup bug. It is an actionable lifetime-corruption issue with demonstrated UAF and write-after-free behavior.

Realistically, the most likely impact is local denial of service through kernel crash. Theoretical escalation is plausible because freed kernel memory can receive device-supplied data and the freed driver object is later dereferenced, but the patch does not demonstrate controlled reclaim or a reliable LPE primitive. Therefore the conservative score is Actionable Moderate, while the paranoid score reaches Strong Important candidate.

## 5. One-sentence report phrase

ALSA us144mkii capture URBs can remain queued after teardown because resubmitted URBs are not re anchored, allowing later USB completions to write device supplied data into freed buffers and dereference a freed driver object, causing kernel UAF and possible local DoS or privilege escalation.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

This issue has confirmed KASAN use-after-free, a freed-buffer write, async completion after teardown, and possible attacker influence through ALSA device access or USB device behavior. It should not be auto-closed.

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UPSTREAM PATCH SUMMARY
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Patch: ALSA: us144mkii: re-anchor capture URBs on resubmission
Commit: 7779249561d14b8a17c0c83783225794e24a587d
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=7779249561d14b8a17c0c83783225794e24a587d

Commit description:

capture_urb_complete() resubmits each capture URB without anchoring it:

	usb_get_urb(urb);
	ret = usb_submit_urb(urb, GFP_ATOMIC);

Anchoring is a property of a submission, not of the URB.  The giveback
path calls usb_unanchor_urb() before urb->complete(), so an URB
resubmitted from its own completion handler is off the anchor.  The
capture URBs are anchored once, at stream start, so from the first
completion onward tascam->capture_anchor is empty.

tascam_free_urbs(), tascam_disconnect(), tascam_suspend() and the
stop-work path all call usb_kill_anchored_urbs(&tascam->capture_anchor)
to reap the capture URBs before anything is freed.  With the anchor empty
those calls return immediately and the URBs stay queued on the host
controller.

tascam_free_urbs() then returns the capture transfer buffers with
usb_free_coherent(), and snd_card_free() releases the snd_card
allocation that embeds tascam (card->private_data).  The controller
completes the queued URBs afterwards, writing device-supplied data into
the freed transfer buffer, and capture_urb_complete() dereferences the
freed driver object.

KASAN on 7.2.0-rc5 (arm64):

  BUG: KASAN: slab-use-after-free in dummy_timer
  Write of size 512 at addr ffff000015b62000
   __asan_memcpy
   dummy_timer
   hrtimer_run_softirq
  Allocated by task 64:
   usb_alloc_coherent
   tascam_alloc_urbs
   tascam_probe
  Freed by task 170:
   usb_free_coherent
   tascam_free_urbs
   tascam_disconnect
   usb_unbind_interface

  BUG: KASAN: slab-use-after-free in capture_urb_complete
  Read of size 4 at addr ffff0000170ee878
  Freed by task 170:
   release_card_device
   snd_card_free
   tascam_disconnect

Restore the usb_anchor_urb() between the reference count bump and the
resubmission.  That also makes the handler's usb_unanchor_urb() failure
arm meaningful again and restores usb_kill_anchored_urbs() as a barrier
on the disconnect, suspend and stop-work paths.

The anchoring was removed on the premise that the URB is already anchored
from the initial submission, which does not hold once the first giveback
has run.

Discovered by XBOW, triaged by Baul Lee <baul.lee@xbow.com>

Fixes: 5cff152 ("ALSA: us144mkii: capture_urb_complete: redundant usb_anchor_urb corrupts anchor list on each resubmission")
Reported-by: Federico Kirschbaum <federico.kirschbaum@xbow.com>
Reported-by: Baul Lee <baul.lee@xbow.com>
Cc: stable@vger.kernel.org
Signed-off-by: Baul Lee <baul.lee@xbow.com>
Link: https://patch.msgid.link/20260804123625.91769-1-baul.lee@xbow.com
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  sound/usb/usx2y/us144mkii_capture.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=7779249561d14b8a17c0c83783225794e24a587d

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

The original Linux kernel CVE announcement for CVE-2026-74639 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74639

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:L/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: 6
  Paranoid ActionableScore: 8

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.
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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).