[CVE-2026-64029][MODERATE 7.0] ALSA: seq: Serialize UMP output teardown with event_input [ Upstream

[CVE-2026-64029][MODERATE 7.0] ALSA: seq: Serialize UMP output teardown with event_input [ Upstream

[AL-KERNEL]

CVE: CVE-2026-64029
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: ALSA: seq: Serialize UMP output teardown with event_input [ Upstream
Commit: 8ba1c4ddbb1c67d34bb440aecb9f5690ed3f64cb
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=8ba1c4ddbb1c67d34bb440aecb9f5690ed3f64cb
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64029
Analysis date: Sun, 19 Jul 2026 21:17:03 -0400
ActionableScore: 5
ActionableScore lower bound: 4
Actionable bucket: Actionable Moderate at minimum
Manual review required: YES

Summary:
A race in ALSA sequencer UMP output teardown can let `seq_ump_process_event()` use a rawmidi substream runtime after the last close releases it, causing a KASAN-confirmed slab-use-after-free in `snd_rawmidi_kernel_write1()` and requiring local manual security review.

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ABOUT THIS REPORT
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The original Linux kernel CVE announcement for CVE-2026-64029 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64029

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-2026-64029	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:L/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:H';BEST CVSS score: '7';DESCR 'ALSA sequencer UMP output handling has a race between seq_ump_process_event() and seq_ump_client_close() on the visible rawmidi output file. An event_input path can borrow client out_rfile output and enter snd_rawmidi_kernel_write1() while the last close path releases the rawmidi file and frees substream runtime, producing a slab use after free in the write path. For the CVSS the PR:L is used because a local user or local process with access to ALSA sequencer and UMP rawmidi interfaces can trigger event delivery and disconnect or close paths without full administrator privileges in many desktop or audio enabled systems. The issue is not network reachable and requires local interaction with sound device interfaces. Impact is at least local denial of service via kernel crash. Because this is a real KASAN confirmed UAF in kernel memory, the paranoid score treats high confidentiality and integrity impact as possible and requires manual review.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate at minimum (with actual score 5)	YES	READ LOCK DANGER INIT UAF HARDWARE LINUS KPANIC 	NO	NO	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=5
ActionableScoreLower=4

## 1. ActionableScore

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

## 2. Signal breakdown

Conservative signals:

* Local unprivileged trigger: +1
  Local users with access to ALSA sequencer and UMP rawmidi paths may trigger event delivery and close or disconnect transitions.

* Memory corruption, weak primitive: +1
  The bug is a KASAN-confirmed slab-use-after-free, but the shown primitive is a race-dependent stale substream/runtime access without demonstrated attacker-controlled reclaim, type confusion, callback control, or arbitrary write.

* Real lifetime corruption: +1
  The patch fixes a real lifetime bug where `client->out_rfile.output` can survive concurrent teardown and `substream->runtime` can be freed while still in use.

* Reliable kernel crash / strong DoS: +1
  KASAN reproduced a slab-use-after-free in `snd_rawmidi_kernel_write1()`, so local kernel crash is realistic.

* Local device-object lifetime control: +1
  The reproducer path involves ALSA sequencer connect/disconnect and event delivery controlling allocation and release through `seq_ump_use()` and `seq_ump_unuse()`.

* Hard race / timing window: -1
  The bug requires overlap between `event_input` and last output close/release.

Paranoid interpretation:

* The same signals apply, but the race appears reproducible and involves a kernel write path over a freed rawmidi runtime object. This supports manual-review sensitivity and raises the practical triage score to 5, while still respecting the race-UAF cap and not assuming a proven LPE primitive.

## 3. Reachability analysis

The bug is locally reachable through ALSA sequencer UMP and rawmidi interfaces. It is not network reachable. Typical triggering requires a local process able to interact with the relevant sound device and sequencer interfaces, not full host root in many desktop or audio-enabled configurations.

Namespaces and containers may matter if sound devices or `/dev/snd/*` are exposed into a container. In a default server deployment without UMP-capable devices or ALSA sequencer exposure, practical reachability is lower. On desktop, workstation, audio, or containerized multimedia systems with sound device access delegated, the attack surface is more realistic.

Call-site confidence: high. The commit message gives the exact racing paths, the allocation and free paths, and the KASAN-confirmed failing function.

## 4. Severity interpretation

This behaves above an ordinary Moderate because it is a real kernel UAF, not just a warning, NULL dereference, or resource leak. Conservative treatment is still bounded because the shown primitive is race-dependent and does not demonstrate controlled reclaim, object replacement, callback dispatch, or arbitrary write.

Realistic impact is local DoS through kernel crash. Theoretical LPE concern exists because this is kernel memory lifetime corruption in a write path, but the provided evidence does not prove exploitability beyond crash. This is therefore an Actionable Moderate at minimum and not suitable for auto-close.

## 5. One-sentence report phrase

A race in ALSA sequencer UMP output teardown can let `seq_ump_process_event()` use a rawmidi substream runtime after the last close releases it, causing a KASAN-confirmed slab-use-after-free in `snd_rawmidi_kernel_write1()` and requiring local manual security review.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

This is a confirmed kernel UAF with local reachability through ALSA device interfaces. Even though the demonstrated impact is crash/DoS and the race-UAF primitive is not proven to support LPE, the memory lifetime corruption class and local user reachability make it unsafe to auto-close.

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

Patch: ALSA: seq: Serialize UMP output teardown with event_input [ Upstream
Commit: 8ba1c4ddbb1c67d34bb440aecb9f5690ed3f64cb
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=8ba1c4ddbb1c67d34bb440aecb9f5690ed3f64cb

Changed files:
  sound/core/seq/seq_ump_client.c
  arch/x86/entry/syscall_64.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=8ba1c4ddbb1c67d34bb440aecb9f5690ed3f64cb

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

The original Linux kernel CVE announcement for CVE-2026-64029 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64029

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).