[CVE-2026-74301][LOW] Bluetooth: btmtk: fix URB leak in alloc_mtk_intr_urb error path [ Upstream

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

CVE: CVE-2026-74301
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: Bluetooth: btmtk: fix URB leak in alloc_mtk_intr_urb error path [ Upstream
Commit: 2643524743b9cc3c6f5f34cde2a8c627d793f21c
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=2643524743b9cc3c6f5f34cde2a8c627d793f21c
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74301
Analysis date: Sun, 16 Aug 2026 07:29:43 -0400
ActionableScore: 2
ActionableScore lower bound: 1
Actionable bucket: Ordinary Moderate / Low-like
Manual review required: NO

Summary:
A missing `usb_free_urb()` in the Bluetooth btmtk ISO transmit error path can leak URB objects when `btmtk_isopkt_pad()` fails, allowing local hardware-specific resource exhaustion but not showing memory corruption or privilege escalation.

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ABOUT THIS REPORT
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The original Linux kernel CVE announcement for CVE-2026-74301 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74301

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: LOW
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
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CVE-2026-74301	LOW	CHECK WITH IMPACT FROM ORIG NN LOW	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H';*CWE-401;*CWE-772;**CWE-400;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '4.7';DESCR 'A URB memory leak in the Bluetooth btmtk driver can occur in alloc_mtk_intr_urb() when btmtk_isopkt_pad() fails after usb_alloc_urb() has already allocated an URB. Repeated triggering of this error path can gradually consume kernel memory and may lead to denial of service through resource exhaustion. For the CVSS the PR:L is used for the paranoid score because a local process capable of reaching the affected Bluetooth ISO transmit path may be sufficient, while direct remote network triggering is not supported by the patch context. The issue is local and hardware specific because it depends on the MediaTek btusb path and the failing ISO packet padding condition. Impact is denial of service only and there is no supported UAF, OOB access, information leak, or privilege escalation primitive.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate / Low-like (with actual score 2)	YES	INIT SIMPLEFIX LEAK ERRORPATH SKB 	YES	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**::

## 2. Signal breakdown

Conservative signals:

* Local trigger: +1. A local process reaching the affected Bluetooth btmtk ISO transmit path may trigger the failing error path.
* Rare hardware / device-specific path: -1. The issue depends on MediaTek btusb support and the ISO packet padding path.
* Availability impact: +1. Repeated leaks could gradually consume kernel memory, but this is not an immediate crash primitive.

Paranoid additional interpretation:

* Availability impact kept as realistic: +1. Sustained repeated triggering may lead to resource exhaustion.
* No memory corruption points. The patch fixes a missing `usb_free_urb()` on an error path, not UAF, OOB, double-free, type confusion, or arbitrary write.
* No privilege escalation points. There is no supported reclaim, overwrite, callback, refcount, or object confusion primitive.
* No remote/network points. Bluetooth radio proximity is not the same as a network-triggerable kernel path here, and the patch context shows a local driver transmit allocation path.

## 3. Reachability analysis

The bug is reachable only on systems using the MediaTek Bluetooth btusb path with ISO data transmission support. Triggering requires reaching `alloc_mtk_intr_urb()` and causing `btmtk_isopkt_pad()` to fail after the URB allocation. This is local and hardware-specific. It is not a generic Bluetooth core bug and not directly network reachable. Namespaces do not obviously lower privileges here unless the product exposes Bluetooth device access to untrusted local users.

Call-site confidence: medium. The immediate error path is clear from the patch, but the full caller chain and exact unprivileged reachability are not included.

## 4. Severity interpretation

This behaves like a Low or ordinary Moderate resource leak. The realistic impact is gradual kernel memory consumption and possible DoS after repeated triggering. Theoretical impact beyond DoS is not supported because the leaked object is not freed incorrectly and no stale pointer reuse or memory corruption primitive is shown. It should not be treated as Important.

## 5. One-sentence report phrase

A missing `usb_free_urb()` in the Bluetooth btmtk ISO transmit error path can leak URB objects when `btmtk_isopkt_pad()` fails, allowing local hardware-specific resource exhaustion but not showing memory corruption or privilege escalation.

## 6. Manual review recommendation

NO MANUAL CHECK NEEDED

Reason: this is a constrained URB memory leak in a device-specific error path, with no concrete memory corruption, information disclosure, privilege escalation, or remote trigger evidence.

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

Patch: Bluetooth: btmtk: fix URB leak in alloc_mtk_intr_urb error path [ Upstream
Commit: 2643524743b9cc3c6f5f34cde2a8c627d793f21c
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=2643524743b9cc3c6f5f34cde2a8c627d793f21c

Changed files:
  drivers/bluetooth/btmtk.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=2643524743b9cc3c6f5f34cde2a8c627d793f21c

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

The original Linux kernel CVE announcement for CVE-2026-74301 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74301

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:N/I:N/A:L
  The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS score: 4.7

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: LOW
KPANIC detected for this report: NO
Published priority for this report (same as in Subject): LOW

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).