[CVE-2026-53241][MODERATE REGULAR] ALSA: seq: dummy: fix UMP event stack overread [ Upstream

[CVE-2026-53241][MODERATE REGULAR] ALSA: seq: dummy: fix UMP event stack overread [ Upstream

[AL-KERNEL]

CVE: CVE-2026-53241
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: ALSA: seq: dummy: fix UMP event stack overread [ Upstream
Commit: a7ef78a2c536242ccb7a4429da01580b2409bb24
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=a7ef78a2c536242ccb7a4429da01580b2409bb24
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53241
Analysis date: Thu, 25 Jun 2026 09:34:59 -0400
ActionableScore: 3
ActionableScore lower bound: 2
Actionable bucket: Borderline manual review recommended / Ordinary Moderate with actionable info leak concern
Manual review required: YES

Summary:
A local ALSA sequencer user may trigger a UMP event stack overread in the dummy client, potentially leaking adjacent kernel stack data, but the patch does not show a write primitive or direct privilege escalation path.

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

The original Linux kernel CVE announcement for CVE-2026-53241 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53241

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 REGULAR
Manual review required: YES

A detailed explanation of the methodology and priority rules is included
at the end of this message.

======================================================================
AL-KERNEL CLASSIFICATION RESULT
======================================================================

CVE-2026-53241	MODERATE	CHECK	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:N/A:N';CWE-126;CWE-125;*CWE-200;Other CVSS 'AV:L/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:N';BEST CVSS score: '5.5';DESCR 'An out-of-bounds stack read in the ALSA sequencer dummy port can occur when a UMP event is copied into legacy snd_seq_event sized stack storage while the UMP flag remains set. The subscriber delivery path can then calculate a UMP sized packet and copy bytes past the end of the stack temporary, which may expose adjacent kernel stack data to a local subscriber. For the CVSS the PR:L is used because triggering requires a local process that can access the ALSA sequencer interface and send or route events through the dummy client. The issue is not network reachable. Impact is primarily confidentiality loss from a bounded kernel stack overread. There is no direct write primitive or UAF shown by the code path.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline manual review recommended / Ordinary Moderate with actionable info leak concern (with actual score 3)	YES	SIMPLEFIX HARDWARE LINUS PACKET  INCREASED_FROM_LOW_BASED_ON_REQUIREMANUALCHECK DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5	YES	NO	checked

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

ActionableScore=3
ActionableScoreLower=2

## 1. ActionableScore

* Conservative score: 2
* Paranoid score: 3
* Final recommended bucket: **Borderline manual review recommended / Ordinary Moderate with actionable info leak concern**

## 2. Signal breakdown

* Local unprivileged trigger: +1. A local process with access to the ALSA sequencer interface can send or route UMP events through the dummy client.
* Confidentiality impact plausible: +1. The bug is an out-of-bounds stack read and may expose adjacent kernel stack bytes through event delivery to subscribers.
* Broad/default/common subsystem or broadly deployed exposure: +1 in paranoid scoring only. ALSA sequencer is a common local kernel interface on desktop and audio-enabled systems, but the affected dummy UMP path is more specific and may not be active everywhere.
* Limited read-only OOB: +0. The patch shows stack overread, not UAF, OOB write, type confusion, arbitrary write, callback corruption, or object lifetime corruption.
* No reliable kernel crash / strong DoS: +0. The described failure mode is overread and possible disclosure, not panic or persistent availability loss.
* No privilege escalation plausible signal: +0. There is no write primitive, reclaim primitive, stale callback, refcount takeover, or demonstrated exploit chain.

## 3. Reachability analysis

The bug is locally reachable through ALSA sequencer event handling when UMP events can be delivered to the dummy sequencer client. It does not appear network reachable. PR:L is the right practical interpretation because a local user process is needed to access the sequencer device and shape the event flow. Containers or sandboxed environments may reduce exposure if ALSA devices are not passed through, but systems exposing `/dev/snd/seq` to untrusted users or containers should treat it as reachable. The path is common enough for manual review, but not comparable to core networking, page cache, io_uring, or netfilter exposure.

## 4. Severity interpretation

This behaves like an ordinary Moderate issue with an actionable confidentiality review requirement. The concrete primitive is a bounded kernel stack overread caused by using legacy-sized stack storage for a larger UMP event while preserving UMP packet semantics. Theoretical usefulness exists because kernel stack disclosure can help other exploit chains, but the patch does not show memory corruption, control-flow influence, write access, or privilege escalation by itself.

## 5. One-sentence report phrase

A local ALSA sequencer user may trigger a UMP event stack overread in the dummy client, potentially leaking adjacent kernel stack data, but the patch does not show a write primitive or direct privilege escalation path.

## 6. Manual review recommendation

MANUAL CHECK RECOMMENDED

Manual review is recommended because this is a kernel information disclosure primitive from stack overread, even though it is local-only and lacks evidence of memory corruption or direct privilege escalation.

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

Patch: ALSA: seq: dummy: fix UMP event stack overread [ Upstream
Commit: a7ef78a2c536242ccb7a4429da01580b2409bb24
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=a7ef78a2c536242ccb7a4429da01580b2409bb24

Changed files:
  sound/core/seq/seq_dummy.c
  sound/core.h
  sound/initval.h
  sound/asoundef.h

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=a7ef78a2c536242ccb7a4429da01580b2409bb24

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

The original Linux kernel CVE announcement for CVE-2026-53241 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53241

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:L/PR:L/UI:N/S:U/C:L/I:N/A:N
  The Best / paranoid CVSS vector: AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N
  The Best / paranoid CVSS score: 5.5

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: 3

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 REGULAR

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).