[CVE-2026-53193][MODERATE 7.0] ALSA: timer: Forcibly close timer instances at closing

[CVE-2026-53193][MODERATE 7.0] ALSA: timer: Forcibly close timer instances at closing

[AL-KERNEL]

CVE: CVE-2026-53193
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: ALSA: timer: Forcibly close timer instances at closing
Commit: 586b219a22b1032b28b8bd356b963276c5e5bf53
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=586b219a22b1032b28b8bd356b963276c5e5bf53
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53193
Analysis date: Thu, 25 Jun 2026 07:45:44 -0400
ActionableScore: 5
ActionableScore lower bound: 4
Actionable bucket: Actionable Moderate at minimum
Manual review required: YES

Summary:
A local use-after-free in the ALSA timer subsystem can occur when snd_timer_free() releases a timer while slave timer instances still reference it, allowing a local user with ALSA timer access to trigger at least a kernel crash and requiring manual review for possible privilege escalation risk.

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

The original Linux kernel CVE announcement for CVE-2026-53193 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53193

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
======================================================================

CVE-2026-53193	MODERATE	CHECK	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-664;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:H';BEST CVSS score: '7';DESCR 'A use-after-free can occur in the ALSA timer subsystem when snd_timer_free() releases a timer object while slave snd_timer_instance objects still reference it through a master/slave timer relationship. A local user can potentially trigger this with user-space driven timers when CONFIG_SND_UTIMER is enabled, because timer objects can be created and deleted through simple open and close operations while another process continues to access related timer instances. For the CVSS the PR:L is used because reliable triggering requires local code execution or access to ALSA timer interfaces, but does not necessarily require full administrator privileges. The issue is not network reachable. Impact is at least local denial of service via kernel crash and in the worst case may allow confidentiality and integrity impact or privilege escalation due to a kernel use-after-free primitive.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate at minimum (with actual score 5)	YES	INIT UAF TIMER HARDWARE LINUS KPANIC  KPANIC DECREASED_TO_MODERATE70_BASED_ON_ACTIONABLESCORELOWERTHAN7	YES	NO	checked

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

ActionableScore=5
ActionableScoreLower=4

## 1. ActionableScore

* Conservative score: 4
* Paranoid score: 5
* Final recommended bucket: **Actionable Moderate at minimum**::

This is a local kernel lifetime bug with a real UAF condition in ALSA timer object teardown. The conservative score is capped because the patch shows stale pointer survival after close/free, but does not show attacker-controlled reclaim, callback hijack, arbitrary write, or a demonstrated LPE primitive. The paranoid score is higher because the bug is explicitly UAF, appears locally triggerable through userspace-driven timers, and deserves manual security review.

## 2. Signal breakdown

Triggered signals:

* Local unprivileged trigger: +1
  CONFIG_SND_UTIMER allows userspace-driven timers, and the commit says the bug can be triggered through simple file open/close while other applications keep accessing the timer.

* Memory corruption, weak/indirect corruption candidate: +1
  The commit explicitly describes a use-after-free condition where slave timer instances can retain references to a freed snd_timer object. No controlled reclaim or overwrite primitive is shown.

* Real lifetime corruption: +1
  This is a stale pointer after object free involving snd_timer and snd_timer_instance lifetime mismatch.

* Reliable kernel crash / strong DoS: +1
  A stale timer pointer in kernel timer paths is realistically crashable when accessed after the backing timer object is freed.

Paranoid additional signal:

* Broad/common local subsystem exposure: +1
  ALSA timer interfaces are ordinary local kernel interfaces on many systems, and the vulnerable path is not a purely theoretical driver-init path.

Not awarded:

* Strong LPE plausibility: +0
  No attacker-controlled reclaim, callback dispatch, type confusion, refcount takeover, or write-after-free is shown in the patch.

* Confidentiality/Integrity impact: +0 conservative
  Possible in worst-case UAF triage, but not demonstrated by the patch.

* Hard race subtraction: 0
  The commit says the bug can be easily triggered with userspace-driven timers, so a strong timing penalty is not appropriate.

## 3. Reachability analysis

A local user or local process with access to ALSA timer interfaces can plausibly trigger the bug. CONFIG_SND_UTIMER increases practical reachability because userspace can create and delete timer objects through open/close while another process keeps related timer instances active. This is not network reachable. Containers and sandboxes matter if ALSA device nodes or timer interfaces are exposed into the container, in which case the practical privilege level may remain low rather than host-root.

## 4. Severity interpretation

This is more than an ordinary Moderate cleanup because the bug class is a real kernel UAF. Realistic evidence supports local DoS and stale object lifetime corruption. However, the patch does not show a concrete privilege escalation primitive such as controlled heap reclaim, function pointer control, arbitrary write, or type confusion. Therefore the conservative interpretation is borderline/manual-review Moderate, while the paranoid interpretation is Actionable Moderate and should not be auto-closed.

## 5. One-sentence report phrase

A local use-after-free in the ALSA timer subsystem can occur when snd_timer_free() releases a timer while slave timer instances still reference it, allowing a local user with ALSA timer access to trigger at least a kernel crash and requiring manual review for possible privilege escalation risk.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

Reason: this is an explicit local kernel UAF in an ordinary userspace-reachable subsystem. Even though the patch does not demonstrate a strong LPE primitive, UAF lifetime bugs in local kernel object APIs should not be auto-closed without manual review.

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

Patch: ALSA: timer: Forcibly close timer instances at closing
Commit: 586b219a22b1032b28b8bd356b963276c5e5bf53
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=586b219a22b1032b28b8bd356b963276c5e5bf53

Commit description:

When snd_timer object is freed via snd_timer_free() and still pending
snd_timer_instance objects are assigned to the timer object, it tries
to unlink all instances and just set NULL to each ti->timer, then
releases the resources immediately.  The problem is, however, when
there are slave timer instances that are associated with a master
instance linked to this timer: namely, those slave instances still
point to the freed timer object although the master instance is
unlinked, which may lead to user-after-free.  The bug can be easily
triggered particularly when a new userspace-driven timers
(CONFIG_SND_UTIMER) is involved, since it can create and delete the
timer object via a simple file open/close, while the other
applications may keep accessing to that timer.

This patch is an attempt to paper over the problem above: now instead
of just unlinking, call snd_timer_close[_locked]() forcibly for each
pending timer instance, so that all assigned slave timer instances are
properly detached, too.  Since snd_timer_close() might be called later
by the driver that created that instance, the check of
SNDRV_TIMER_IFLG_DEAD is added at the beginning, too.

Reported-by: Kyle Zeng <kylebot@openai.com>
Tested-by: Kyle Zeng <kylebot@openai.com>
Fixes: 3774591 ("ALSA: timer: Introduce virtual userspace-driven timers")
Cc: stable@vger.kernel.org
Link: https://patch.msgid.link/20260606161145.1933447-1-tiwai@suse.de
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  sound/core/timer.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=586b219a22b1032b28b8bd356b963276c5e5bf53

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

The original Linux kernel CVE announcement for CVE-2026-53193 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53193

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: 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).