[CVE-2026-74502][IMPORTANT] ALSA: ump: fix double free of out_cvts on rawmidi error

[CVE-2026-74502][IMPORTANT] ALSA: ump: fix double free of out_cvts on rawmidi error

[AL-KERNEL]

CVE: CVE-2026-74502
Priority: IMPORTANT
AL-KERNEL base severity: IMPORTANT
KPANIC flag: YES
Patch: ALSA: ump: fix double free of out_cvts on rawmidi error
Commit: e84d2e53a05c78a04d1343eeb0f31a79456e79fc
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=e84d2e53a05c78a04d1343eeb0f31a79456e79fc
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74502
Analysis date: Sat, 15 Aug 2026 09:02:31 -0400
ActionableScore: 6
ActionableScore lower bound: 5
Actionable bucket: Actionable Moderate at minimum
Manual review required: YES

Summary:
A malicious USB MIDI 2.0 UMP device can trigger an ALSA rawmidi error path that leaves `ump->out_cvts` dangling after `kfree()`, causing a later endpoint teardown to double free the same allocation and potentially crash the kernel.

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

The original Linux kernel CVE announcement for CVE-2026-74502 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74502

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
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CVE-2026-74502	IMPORTANT	CHECK WITH IMPACT FROM ORIG NN MODERATE	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:P/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H';CWE-415;*CWE-416;*CWE-672;CWE-415;Other CVSS 'AV:P/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '6.8';DESCR 'ALSA UMP rawmidi error handling can leave ump out_cvts pointing to freed memory after snd_rawmidi_new() fails. During later endpoint teardown, snd_ump_endpoint_free() may free the same allocation again, producing a kernel double free. For the CVSS the PR:N is used because a malicious USB MIDI 2.0 device does not need an authenticated user account on the target. The issue is not network reachable. In practice exploitation requires physical access to attach a malicious USB MIDI 2.0 device or another path that can present a controlled USB device to the host. Impact is at least denial of service via kernel memory corruption and crash. In the paranoid interpretation, double free memory corruption may have confidentiality and integrity impact and should be manually reviewed.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate at minimum (with actual score 7)	YES	DANGER ERRORPATH UAF HARDWARE LINUS KPANIC  KPANIC INCREASED_TO_HIGH_BASED_ON_ACTIONABLESCOREHIGHEREQTHAN6	YES	NO	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=6
ActionableScoreLower=5

## 1. ActionableScore

* Conservative score: **5**
* Paranoid score: **6**
* Final recommended bucket: **Actionable Moderate at minimum**::

## 2. Signal breakdown

Triggered signals:

* **Firmware/device-mediated external influence: +1**
  A malicious or malformed USB MIDI 2.0 UMP device can influence enumeration and reach the failing `snd_rawmidi_new()` path.

* **Generic memory corruption, strong corruption primitive: +2**
  The bug is a real kernel **double free** of `ump->out_cvts`.

* **Real lifetime corruption: +1**
  The pointer remains dangling after `kfree()` and is later freed again during endpoint teardown.

* **Reliable kernel crash / strong DoS: +1**
  A double free in kernel memory is a credible crash path, even if exploitation beyond DoS is not demonstrated.

* **Privileged kernel/device-management memory corruption path: +1**
  The corruption occurs in USB/ALSA device enumeration and teardown handling, driven by an external device.

Subtracted signals:

* **Physical-only or rare hardware-only condition: -2**
  Practical exploitation requires physical USB access or an equivalent USB device emulation path.

Paranoid-only additional concern:

* **Weak LPE concern: +1**
  Double free is a memory corruption class that can sometimes become more than DoS, but this patch does not show attacker-controlled reclaim, overwrite target, callback control, or type confusion.

## 3. Reachability analysis

The bug is reachable when the host enumerates a USB MIDI 2.0 UMP device and the device or environment causes `snd_rawmidi_new()` to fail after `ump->out_cvts` has been allocated. No local authenticated user account is required in the CVSS sense if the attacker controls the USB device, but practical access is physical or device-emulation based, not network reachable.

Namespaces and containers do not materially help ordinary remote attackers because the trigger is in host USB device enumeration. The path is relevant on systems with ALSA USB MIDI 2.0 UMP support, but it is not a broad remote attack surface.

Call-site confidence: **high**, because the patch and commit directly describe the first `kfree()` on the error path and the later second free in `snd_ump_endpoint_free()`.

## 4. Severity interpretation

This is not an ordinary low-risk cleanup because it fixes a concrete kernel double free. Realistic impact is likely host kernel crash or DoS from a malicious USB MIDI 2.0 device. Privilege escalation is not demonstrated, but the memory corruption class is strong enough to avoid auto-close and to require manual review.

This behaves as **Actionable Moderate**, with a paranoid upper bound near **Important candidate** only if further analysis shows attacker-controlled heap reuse or a stronger exploitation primitive.

## 5. One-sentence report phrase

A malicious USB MIDI 2.0 UMP device can trigger an ALSA rawmidi error path that leaves `ump->out_cvts` dangling after `kfree()`, causing a later endpoint teardown to double free the same allocation and potentially crash the kernel.

## 6. Manual review recommendation

**MANUAL CHECK REQUIRED**

Reason: this is confirmed kernel memory corruption through double free, even though the practical exposure is physical USB rather than network reachable.

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

Patch: ALSA: ump: fix double free of out_cvts on rawmidi error
Commit: e84d2e53a05c78a04d1343eeb0f31a79456e79fc
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=e84d2e53a05c78a04d1343eeb0f31a79456e79fc

Commit description:

snd_ump_attach_legacy_rawmidi() allocates the legacy conversion array
ump->out_cvts and, on the snd_rawmidi_new() error path, frees it with
kfree() but leaves ump->out_cvts pointing at the freed memory.  When the
endpoint is later torn down, snd_ump_endpoint_free() frees ump->out_cvts
a second time, resulting in a double free.

The host snd-usb-audio driver attaches the legacy rawmidi for any USB
MIDI 2.0 (UMP) device, so a device that makes snd_rawmidi_new() fail
reaches this path on enumeration.

Clear ump->out_cvts after freeing it on the error path so it is not
freed again during teardown.

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

Fixes: 33cd763 ("ALSA: ump: Export MIDI1 / UMP conversion helpers")
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/20260726051633.41206-1-baul.lee@xbow.com
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  sound/core/ump.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=e84d2e53a05c78a04d1343eeb0f31a79456e79fc

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

The original Linux kernel CVE announcement for CVE-2026-74502 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74502

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:N/I:N/A:H
  The Best / paranoid CVSS vector: AV:P/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
  The Best / paranoid CVSS score: 6.8

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: 5
  Paranoid ActionableScore: 6

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).