[CVE-2026-52963][MODERATE REGULAR] ALSA: usb-audio: Bound MIDI endpoint descriptor scans

[CVE-2026-52963][MODERATE REGULAR] ALSA: usb-audio: Bound MIDI endpoint descriptor scans

[AL-KERNEL]

CVE: CVE-2026-52963
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: ALSA: usb-audio: Bound MIDI endpoint descriptor scans
Commit: e2f1260a056eb3215c13c48c5378f3e4112dc3af
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=e2f1260a056eb3215c13c48c5378f3e4112dc3af
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-52963
Analysis date: Wed, 24 Jun 2026 15:17:30 -0400
ActionableScore: 2
ActionableScore lower bound: 1
Actionable bucket: Ordinary Moderate / Low-like physical-only issue
Manual review required: NO

Summary:
No one-sentence report phrase was found.

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

The original Linux kernel CVE announcement for CVE-2026-52963 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-52963

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: NO

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-2026-52963	MODERATE	CHECK	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:P/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:H';CWE-125;*CWE-20;CWE-130;Other CVSS 'AV:P/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:L';BEST CVSS score: '5.7';DESCR 'A malformed USB MIDI endpoint extra descriptor can make the ALSA usb-audio descriptor walker accept a class specific endpoint descriptor whose bLength extends beyond the remaining endpoint extra buffer. Later MIDIStreaming parsing can then read flexible array fields such as baAssocJackID using bLength rather than the real remaining buffer size, creating an out-of-bounds read in kernel context. For the CVSS the PR:N is used because a malicious USB device can trigger descriptor parsing without requiring an account or privileges on the target system. The attack vector is physical because the attacker normally needs to attach or emulate a malicious USB device. Impact is at least a local physical denial of service or limited kernel memory exposure through invalid descriptor parsing. YES REQUIRES MANUAL CHECK';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate / Low-like physical-only issue (with actual score 2)	YES	USB SIMPLEFIX HARDWARE LINUS  INCREASED_FROM_LOW_BASED_ON_REQUIREMANUALCHECK DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5	NO	NO	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=2
ActionableScoreLower=1

1. ActionableScore
* Conservative score: 1
* Paranoid score: 2
* Final recommended bucket: **Ordinary Moderate / Low-like physical-only issue**

2. Signal breakdown
* Limited read-only OOB / weak corruption concern: +0. The patch fixes a descriptor walker that could accept a USB MIDI endpoint descriptor whose bLength exceeds the remaining buffer. This supports an OOB read class, not an OOB write, UAF, double-free, or arbitrary overwrite.
* Confidentiality impact plausible: +1. A bounded but invalid kernel-context read from adjacent descriptor memory is plausible, although no clear user-visible disclosure path is shown.
* Availability impact realistic: +1. Malformed USB descriptors can plausibly cause a crash, warning, or driver failure during parsing, but the patch does not demonstrate a reliable host-wide panic.
* Broad/common subsystem exposure: +1. USB audio is a common kernel subsystem, and descriptor parsing is normally automatic when a device is attached.
* Physical-only attack surface: -2. Realistic triggering requires attaching or emulating a malicious USB MIDI/audio device. This is not network reachable and does not require a local user account on the target.

3. Reachability analysis
A malicious physical USB device or USB emulation environment can trigger the path during ALSA usb-audio MIDI descriptor parsing. No Linux user account or privileges are required once the device is connected, so the CVSS-style PR is effectively PR:N, but the attack vector is physical. Namespaces and containers do not materially lower the requirement because the vulnerable parsing happens in the host kernel during device enumeration or driver probing. The path is common on systems that allow USB audio devices, but exploitation requires physical or equivalent USB-level access.

4. Severity interpretation
This behaves more like an ordinary Moderate or Low-like physical attack surface issue than an Important kernel vulnerability. The theoretical issue is kernel OOB read during descriptor parsing, with possible crash or limited memory exposure. Realistic exploitation evidence is weak because the patch shows bounds validation for flexible-array reads, not attacker-controlled overwrite, lifetime corruption, callback control, object replacement, or privilege escalation. It should not be auto-promoted to Important based only on the memory-safety label.

5. One-sentence report phrase
A malformed USB MIDI endpoint descriptor can make ALSA usb-audio parse beyond the remaining endpoint extra buffer, causing a physical-attack-surface OOB read with possible limited memory exposure or DoS, but no demonstrated privilege escalation primitive.

6. Manual review recommendation
MANUAL CHECK RECOMMENDED. The issue is low-actionability because it is physical-only and read-oriented, but it is still a kernel OOB read in a common USB parsing path and should receive at least lightweight manual review before closure.

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

Patch: ALSA: usb-audio: Bound MIDI endpoint descriptor scans
Commit: e2f1260a056eb3215c13c48c5378f3e4112dc3af
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=e2f1260a056eb3215c13c48c5378f3e4112dc3af

Commit description:

snd_usbmidi_get_ms_info() validates the internal MIDIStreaming endpoint
descriptor size before using baAssocJackID[], but the descriptor walker can
still return a class-specific endpoint descriptor whose bLength exceeds the
remaining bytes in the endpoint-extra scan.

That leaves later flexible-array reads bounded by bLength, but not by the
remaining bytes in the endpoint-extra scan.

Stop walking when bLength is zero or
extends past the remaining endpoint-extra scan.

Fixes: 5c6cd70 ("ALSA: usb-audio: Fix case when USB MIDI interface has more than one extra endpoint descriptor")
Cc: stable@vger.kernel.org
Signed-off-by: Cássio Gabriel <cassiogabrielcontato@gmail.com>
Link: https://patch.msgid.link/20260507-usb-midi-endpoint-scan-bounds-v1-1-329d7348160e@gmail.com
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  sound/usb/midi.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=e2f1260a056eb3215c13c48c5378f3e4112dc3af

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

The original Linux kernel CVE announcement for CVE-2026-52963 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-52963

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:P/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:L
  The Best / paranoid CVSS vector: AV:P/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:H
  The Best / paranoid CVSS score: 5.7

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: 1
  Paranoid ActionableScore: 2

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).