[CVE-2026-74503][IMPORTANT] ALSA: timer: Clear SNDRV_TIMER_IFLG_DEAD once the close completes commit c2744d5f3aea474513fd2298daecb94a952ce441 upstream.

[CVE-2026-74503][IMPORTANT] ALSA: timer: Clear SNDRV_TIMER_IFLG_DEAD once the close completes commit c2744d5f3aea474513fd2298daecb94a952ce441 upstream.

[AL-KERNEL]

CVE: CVE-2026-74503
Priority: IMPORTANT
AL-KERNEL base severity: IMPORTANT
KPANIC flag: YES
Patch: ALSA: timer: Clear SNDRV_TIMER_IFLG_DEAD once the close completes commit c2744d5f3aea474513fd2298daecb94a952ce441 upstream.
Commit: bb016091010ec401a06e6bdace0cd944ee03d371
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=bb016091010ec401a06e6bdace0cd944ee03d371
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74503
Analysis date: Sat, 15 Aug 2026 17:17:00 -0400
ActionableScore: 8
ActionableScore lower bound: 7
Actionable bucket: Strong Important candidate / Actionable Moderate at minimum
Manual review required: YES

Summary:
A local unprivileged user with access to ALSA timer and sequencer devices can trigger a stale close/reopen state that frees an ALSA timer instance while it remains linked, causing a UAF with reliable DoS and plausible local privilege escalation impact.

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

The original Linux kernel CVE announcement for CVE-2026-74503 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74503

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: IMPORTANT
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-2026-74503	IMPORTANT	CHECK WITH IMPACT FROM ORIG NN IMPORTANT	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-416;*CWE-664;CWE-362;*CWE-672;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H';BEST CVSS score: '7.8';DESCR 'A use-after-free can occur in the ALSA timer close and reopen path because SNDRV_TIMER_IFLG_DEAD remains set after a completed close. A reopened timer instance can later be freed while it is still linked from timer lists and can still hold slave ownership and timer references. The stale object can be dereferenced by later timer opens, slave checks, or /proc/asound/timers, which makes the impact at least a local kernel crash and a plausible local privilege escalation candidate. For the CVSS the PR:L is used because an unprivileged local user with access to /dev/snd/timer and /dev/snd/seq can reach the affected interfaces. The issue is not network reachable. Impact is rated as C:H/I:H/A:H for the paranoid score because the bug is a real UAF with stale list membership and later dereference paths, not just a warning or resource leak.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 8)  SKIP CVE-2026-74503 UNKNOWN SKIP The Fixes patch not applied yet, so unlikely that actual: da3039e91d1f835874ed6e9a33ea19ee80c2cb92 YES  NO NO unknown 	MAYBE	UAF TIMER HARDWARE LINUS KPANIC 	-	-	checked

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

ActionableScore=8
ActionableScoreLower=7

## 1. ActionableScore

* Conservative score: **7**
* Paranoid score: **8**
* Final recommended bucket: **Strong Important candidate / Actionable Moderate at minimum**::

## 2. Signal breakdown

Triggered signals:

* **Local unprivileged trigger: +1**
  The commit explicitly states that an unprivileged user with access to `/dev/snd/timer` and `/dev/snd/seq` can force the failure path.

* **Generic memory corruption, strong corruption primitive: +2**
  This is a real UAF: `snd_timer_instance_free()` can free an instance that remains linked on timer lists and can later be dereferenced.

* **Real lifetime corruption: +1**
  The bug is caused by stale lifetime state: `SNDRV_TIMER_IFLG_DEAD` remains set after close, causing a reopened object to skip unlinking and then be freed while still reachable.

* **Privilege escalation plausible: +1 conservative / +2 paranoid**
  Conservative score uses weak LPE concern because the patch demonstrates UAF and stale list membership, but does not show controlled reclaim or a write primitive. Paranoid score uses stronger LPE plausibility because the freed object remains reachable through multiple later paths, including timer open, slave checks, and `/proc/asound/timers`.

* **Reliable kernel crash / strong DoS: +1**
  The commit describes a later dereference of the freed instance and a fault on stale `ti->owner`.

* **Broad/default/common subsystem exposure: +1**
  ALSA timer and sequencer device nodes are common on desktop and audio-enabled systems, and access may be delegated to non-root users through audio-related permissions.

Not applied:

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

* **Hard or unreliable race: 0**
  Although the bug is state/lifetime related, the described trigger is a forced close/reopen/error-path sequence, not a narrow timing-only race.

* **Requires admin/root/CAP_*: 0**
  The commit explicitly gives an unprivileged device-node trigger.

## 3. Reachability analysis

The bug is locally reachable by a user that can access both ALSA timer and sequencer interfaces. In typical desktop or audio-capable environments, this may include users in an audio-related group or processes granted access to `/dev/snd/*`. Containers usually do not expose these device nodes by default, but if ALSA devices are passed through, the privilege requirement can effectively remain low inside that environment. The path is not network reachable and does not require CAP_SYS_ADMIN or CAP_NET_ADMIN according to the commit description. Call-site confidence: **high**, because the commit message identifies the reopen path, stale list membership, later dereference paths, and the exact missing flag clear.

## 4. Severity interpretation

This behaves more like an **Important-class local kernel vulnerability candidate** than an ordinary Moderate. The realistic demonstrated impact is a local kernel crash through UAF dereference. The theoretical but technically plausible higher impact is local privilege escalation because the freed timer instance remains linked in kernel lists and can be reached by later operations. The patch does not demonstrate an arbitrary write, callback hijack, or controlled reclaim, so the conservative score avoids treating LPE as proven. The paranoid score is higher because UAF plus stale list reachability in a common local device interface is historically risky and should not be auto-closed.

## 5. One-sentence report phrase

A local unprivileged user with access to ALSA timer and sequencer devices can trigger a stale close/reopen state that frees an ALSA timer instance while it remains linked, causing a UAF with reliable DoS and plausible local privilege escalation impact.

## 6. Manual review recommendation

**MANUAL CHECK REQUIRED. YES REQUIRES MANUAL CHECK.**

Reason: this is a real local UAF with stale list membership and multiple later dereference paths, reachable from unprivileged ALSA device interfaces in some deployments.

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

Patch: ALSA: timer: Clear SNDRV_TIMER_IFLG_DEAD once the close completes commit c2744d5f3aea474513fd2298daecb94a952ce441 upstream.
Commit: bb016091010ec401a06e6bdace0cd944ee03d371
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=bb016091010ec401a06e6bdace0cd944ee03d371

Commit description:

snd_timer_close_locked() marks an instance with SNDRV_TIMER_IFLG_DEAD
and returns early when the flag is already set, but the flag is never
cleared again.  A completed close ends in remove_slave_links(), which
leaves timeri->timer NULL, so a second close is already harmless through
the timer == NULL path; the early return can only be reached by an
instance that was opened again in between.  For such an instance the
close unlinks nothing, so snd_timer_instance_free() frees an object that
is still on timer->open_list_head, still on snd_timer_master_list if it
was opened with a slave key, still owns any adopted slaves, and still
holds its timer and module references.

snd_seq_timer_open() reopens an instance exactly like that: it retries
its fallback open on the same object after a failure that has already
run snd_timer_close_locked() internally.  An unprivileged user with
access to /dev/snd/timer and /dev/snd/seq can force that failure, since
snd_timer_check_master() returns -EBUSY when a pending slave matches the
new master's (slave_class, slave_id) key and the target timer has
reached max_instances, and SNDRV_TIMER_IOCTL_SELECT with dev_class =
SNDRV_TIMER_CLASS_SLAVE keeps the caller-supplied dev_sclass, so a
sequencer queue's key can be forged.  The freed instance is afterwards
dereferenced by any further snd_timer_open() on that timer, by
snd_timer_check_slave(), and by /proc/asound/timers, which faults on the
stale ti->owner pointer.

The flag only has to be visible while the close is in progress, which is
all its other users need.  Clear it in remove_slave_links(), under the
same timer->lock that sets it, once the instance is off every list.

Fixes: da3039e91d1f ("ALSA: timer: Forcibly close timer instances at closing")
Cc: stable@vger.kernel.org
Assisted-by: Claude:claude-opus-5
Signed-off-by: Norbert Szetei <norbert@doyensec.com>
Link: https://patch.msgid.link/CA41AA48-75BF-45E9-A36D-3A5D2F124F60@doyensec.com
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat -rw-r--r-- sound/core/timer.c 2

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=bb016091010ec401a06e6bdace0cd944ee03d371

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

The original Linux kernel CVE announcement for CVE-2026-74503 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74503

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:H/I:H/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: 7
  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: IMPORTANT
KPANIC detected for this report: YES
Published priority for this report (same as in Subject): IMPORTANT

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).