[CVE-2026-80973][MODERATE 7.0] ALSA: 6fire: bound the MIDI event length from the device

[AL-KERNEL <alkernel@kernelcve.org>]

CVE: CVE-2026-80973
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: ALSA: 6fire: bound the MIDI event length from the device
Commit: 466e911bbbbb779bb06337e35a286e5ca7af16b3
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=466e911bbbbb779bb06337e35a286e5ca7af16b3
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80973
Analysis date: Fri, 11 Sep 2026 18:57:34 -0400
ActionableScore: 5
ActionableScore lower bound: 4
Actionable bucket: Actionable Moderate / Strong Important candidate requiring manual review
Manual review required: YES

Summary:
No one-sentence report phrase was found.

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

The original Linux kernel CVE announcement for CVE-2026-80973 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80973

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.

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

CVE-2026-80973	MODERATE	https://www.kernelcve.org/list/?q=CVE-2026-80973 CHECK WITH IMPACT FROM ORIG NN LOW	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:P/AC:L/PR:N/UI:R/S:U/C:H/I:N/A:H';CWE-125;CWE-126;*CWE-20;*CWE-200;Other CVSS 'AV:P/AC:L/PR:N/UI:R/S:U/C:H/I:N/A:L';BEST CVSS score: '5.9';DESCR 'A slab out-of-bounds read in the ALSA usb 6fire MIDI receive path occurs because usb6fire_comm_receiver_handler trusted a length byte supplied by the USB device without bounding it to the 62 bytes available after the two byte header. A malicious or emulated device can report a MIDI event type 0x10 with an excessive length such as 0xff, causing snd_rawmidi_receive to read beyond the 64 byte receiver buffer and potentially expose adjacent kernel heap bytes through the rawmidi read path. For the CVSS the PR:N because the attacker does not need an account on the victim and only needs control of the attached USB device behavior. UI:R is used because the victim side normally needs device attachment and a MIDI input substream must be open for forwarding to userspace. The issue is not network reachable in the usual deployment model. Impact is primarily kernel memory disclosure with possible denial of service if the out-of-bounds read faults or is caught by hardening.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate / Strong Important candidate requiring manual review (with actual score 5)	YES	READ KASAN OOB USB HARDWARE LINUS KPANIC PACKET 	NO	NO	checked

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

ActionableScore=5
ActionableScoreLower=4
PrimitiveClass=CLASS_A
RealUAF=NO
HostAdminRequired=NO
NamespaceScopedPrivilege=NO
ImportantCandidate=YES
ManualReview=REQUIRED
AutoDowngradeAllowed=NO

1. ActionableScore

* Raw conservative score: 4
* Conservative score: 4. No floor or cap applied.
* Raw paranoid score: 5
* Paranoid score: 5. No floor or cap applied.
* Final recommended bucket: **Actionable Moderate / Strong Important candidate requiring manual review**::

2. Signal breakdown

Conservative signals:

* +2. Established user-visible kernel disclosure primitive. A device-controlled MIDI length can make `snd_rawmidi_receive()` read beyond a 64-byte kernel buffer, and the bytes past the buffer are handed to userspace through the rawmidi read path.
* +1. Firmware/device-mediated external influence. The attacker-controlled input is supplied by a malicious or emulated USB device rather than by ordinary network traffic.
* +1. Confidentiality impact is plausible and directly supported. The out-of-bounds bytes are not only read internally but forwarded to userspace.
* +1. Memory layout invariant restoration. The patch restores consistency between declared MIDI event length, fixed 64-byte receiver buffer size, and `urb->actual_length`.
* -1. Concrete physical/specialized-device constraint. Triggering requires a compatible malicious or emulated USB 6fire-like device and practical disclosure also needs a MIDI input substream open.

Paranoid additional signal:

* +1. Possible strong DoS. The KASAN trace demonstrates a slab out-of-bounds read, and on hardened or faulting configurations the same path may crash the kernel.

Important non-awarded signals:

* RealUAF not awarded. No post-free object use is established.
* Controlled reclaim not demonstrated.
* Arbitrary write not demonstrated.
* Integrity impact not awarded. The primitive is an out-of-bounds read, not a write.
* Remote reachability not established. This is USB/device-mediated, not a network service.
* Extra availability not awarded beyond the paranoid crash point.
* Repeated release/refcount signal not applicable.

3. Reachability analysis

The direct attacker model is a malicious or emulated USB device that can control the 6fire communication packet contents, especially the MIDI event type and length byte. Host administrator privilege is not required by the attacker, so `HostAdminRequired=NO`.

This is not namespace-scoped. Network namespaces, user namespaces, and delegated capabilities are not material to the trigger. The issue is also not directly network reachable in the ordinary deployment model.

A prior victim-side condition exists for the confidentiality path: a MIDI input substream must be open because `usb6fire_midi_in_received()` forwards data only when `rt->in` is set. The receiver URB is submitted at probe, so the malformed device response can occur on plug with no special user action for the kernel-side OOB read itself.

The hardware condition is specialized but concrete: the driver must bind to a TerraTec DMX 6Fire USB-compatible device or an emulated device presenting compatible behavior.

4. Primitive and severity interpretation

The exact primitive is a slab out-of-bounds read from a fixed 64-byte USB receiver buffer caused by trusting a device-supplied length up to 255. This is fixed stale storage or fixed buffer misuse, not an active structured-object UAF.

The important severity factor is that the over-read data is copied into the ALSA rawmidi receive path and can become visible to userspace. That makes this stronger than an internal-only OOB read or a pure crash bug.

This is `CLASS_A` because a concrete kernel heap information disclosure path is established. The demonstrated consequence is kernel memory disclosure, with possible DoS if the OOB read faults or is caught by hardening. Privilege escalation is not demonstrated, and no write primitive is shown.

`ImportantCandidate=YES` because kernel heap disclosure through a device-controlled OOB read should not be automatically downgraded without manual review. `AutoDowngradeAllowed=NO` because a concrete disclosure primitive exists.

5. One-sentence report phrase

A malicious or emulated USB 6fire device can supply an oversized MIDI event length that makes the ALSA rawmidi path read beyond a 64-byte kernel buffer and potentially disclose adjacent kernel heap memory to userspace.

6. Manual review recommendation

MANUAL CHECK REQUIRED

Reason: this is a confirmed slab out-of-bounds read with a plausible kernel heap disclosure path to userspace, even though the trigger is physical or device-mediated rather than network-reachable.

7. Call-site confidence

Call-site confidence: high

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

Patch: ALSA: 6fire: bound the MIDI event length from the device
Commit: 466e911bbbbb779bb06337e35a286e5ca7af16b3
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=466e911bbbbb779bb06337e35a286e5ca7af16b3

Commit description:

usb6fire_comm_receiver_handler() forwards a MIDI event using a length
byte the device supplies, with no bound and no check that the transfer
delivered that many bytes:

	if (!urb->status) {
		if (rt->receiver_buffer[0] == 0x10) /* midi in event */
			if (midi_rt)
				midi_rt->in_received(midi_rt,
						rt->receiver_buffer + 2,
						rt->receiver_buffer[1]);
	}

receiver_buffer is a 64-byte kzalloc() buffer (COMM_RECEIVER_BUFSIZE), so
only 62 bytes follow the two-byte header.  receiver_buffer[1] is a u8 the
device chooses, so a device that answers with 0x10 and a length of 0xFF
makes snd_rawmidi_receive() read 255 bytes starting two bytes into a
64-byte object.  The bytes past the buffer are handed to userspace
through the rawmidi read path.

urb->actual_length is not consulted either, so a short transfer leaves
both the type byte and the length byte at their previous values and the
handler acts on stale data.

The receiver URB is submitted from usb6fire_comm_init() at probe, so the
read happens on plug with no user action; forwarding to userspace also
needs a MIDI input substream open, since usb6fire_midi_in_received()
only calls snd_rawmidi_receive() when rt->in is set.

KASAN on 7.2.0-rc5 (arm64), single packet from an emulated device:

  BUG: KASAN: slab-out-of-bounds in snd_rawmidi_receive
  Read of size 255 at addr ffff000009f64682 by task bash/183
   __asan_memcpy
   snd_rawmidi_receive
   usb6fire_midi_in_received [snd_usb_6fire]
   usb6fire_comm_receiver_handler [snd_usb_6fire]
  Allocated by task 11:
   usb6fire_comm_init [snd_usb_6fire]
   usb6fire_chip_probe [snd_usb_6fire]
  The buggy address is located 2 bytes inside of
   allocated 64-byte region [ffff000009f64680, ffff000009f646c0)

Reject the event when the length exceeds the bytes that follow the
header, and require the transfer to have delivered the header plus that
many bytes.  The receiver URB is submitted with a 64-byte
transfer_buffer_length, so a genuine device cannot deliver an event
longer than those 62 bytes and nothing valid is dropped.

Discovered by XBOW, triaged by Baul Lee <baul.lee@xbow.com>

Fixes: c6d43ba ("ALSA: usb/6fire - Driver for TerraTec DMX 6Fire USB")
Reported-by: Federico Kirschbaum <federico.kirschbaum@xbow.com>
Reported-by: Baul Lee <baul.lee@xbow.com>
Cc: stable@vger.kernel.org
Signed-off-by: Baul Lee <baul.lee@xbow.com>
Link: https://patch.msgid.link/20260805013423.38175-1-baul.lee@xbow.com
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  sound/usb/6fire/comm.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=466e911bbbbb779bb06337e35a286e5ca7af16b3

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

The original Linux kernel CVE announcement for CVE-2026-80973 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80973

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:R/S:U/C:H/I:N/A:L
  The Best / paranoid CVSS vector: AV:P/AC:L/PR:N/UI:R/S:U/C:H/I:N/A:H
  The Best / paranoid CVSS score: 5.9

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).