[CVE-2026-64471][MODERATE 7.0] Bluetooth: btusb: fix use-after-free on registration failure

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

CVE: CVE-2026-64471
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: Bluetooth: btusb: fix use-after-free on registration failure
Commit: e09ac7d0c6859a360bf36e7104aef03f88184e0b
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=e09ac7d0c6859a360bf36e7104aef03f88184e0b
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64471
Analysis date: Sat, 25 Jul 2026 09:35:34 -0400
ActionableScore: 5
ActionableScore lower bound: 4
Actionable bucket: Strong Important candidate / Actionable Moderate at minimum
Manual review required: YES

Summary:
A btusb probe error path can leave sibling USB interfaces bound to freed driver state after hci_register_dev() failure, causing use-after-free or double-free on later disconnect and requiring manual review because the issue is kernel lifetime corruption reachable through malicious or faulty USB device behavior.

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

The original Linux kernel CVE announcement for CVE-2026-64471 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64471

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-2026-64471	MODERATE	CHECK WITH IMPACT FROM ORIG NN LOW	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:P/AC:H/PR:N/UI:R/S:U/C:H/I:H/A:H';*CWE-416;CWE-415;CWE-404;Other CVSS 'AV:P/AC:H/PR:N/UI:R/S:U/C:L/I:L/A:H';BEST CVSS score: '6.3';DESCR 'A use-after-free and double-free condition can occur in the Bluetooth btusb probe error path when hci_register_dev fails after sibling USB interfaces have already been associated with the driver state. The failed registration path freed the main device state without releasing the diag and isoc sibling interfaces, so a later disconnect could operate on stale interface data and touch already freed memory. For the CVSS the PR:N is used because the attacker model can be a malicious or faulty USB Bluetooth device attached to the target, not an authenticated local user account. The issue is not network reachable over Bluetooth or IP and requires physical device attachment or an equivalent trusted USB redirection path. Impact is at least denial of service via kernel crash and in worst case may allow confidentiality or integrity impact because the bug class is kernel use-after-free and double-free.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 5)	YES	USB INIT LEAK UAF  KPANIC INCREASED_TO_MODERATE_FROM_LOW_BASED_ON_GUESSCVSS	NO	NO	checked

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

ActionableScore=5
ActionableScoreLower=4

## 1. ActionableScore

* Conservative score: 4
* Paranoid score: 5
* Final recommended bucket: **Strong Important candidate / Actionable Moderate at minimum**::

## 2. Signal breakdown

Triggered signals:

* Generic memory corruption: +2
  The commit explicitly says the bug can cause use-after-free and double-free.
* Real lifetime corruption: +1
  The bug is caused by not releasing sibling USB interfaces before freeing the main btusb state.
* Reliable kernel crash / strong DoS: +1
  A later disconnect can operate on stale interface data and plausibly crash the kernel.
* Firmware-mediated external influence: +1
  The practical attacker model is a malicious, faulty, or emulated USB Bluetooth device influencing probe and disconnect behavior.
* Privileged kernel/device-management memory corruption path: +1
  The bug occurs in USB Bluetooth driver probe/error handling and affects kernel-owned device lifetime state.
* Broad/default/common subsystem: +1
  btusb is a common Bluetooth USB driver and has existed in stable-supported paths for a long time.

Negative signals:

* Physical-only or rare hardware-only condition: -2
  The realistic trigger requires physical USB attachment, USB redirection, or equivalent device emulation.
* Hard or unreliable race / special timing or state required: -1
  The bug requires hci_register_dev() failure after sibling interfaces were already claimed, followed by later disconnect.
* Corruption primitive constrained or not demonstrated as controllable: -1 for conservative score
  The patch shows UAF/double-free, but does not show attacker-controlled reclaim, object replacement, function pointer control, or arbitrary write.

Paranoid adjustment:

* Weak LPE concern: +1
  For paranoid triage only, kernel UAF plus double-free in a device disconnect path is enough to avoid auto-close and require manual review, even though no concrete exploit primitive is demonstrated.

## 3. Reachability analysis

The issue is not network reachable over Bluetooth or IP. The realistic trigger is a local physical or virtual USB path where a malicious, faulty, or emulated Bluetooth USB device reaches the btusb probe path, causes controller registration failure, and is later disconnected.

No authenticated local Linux user account is necessarily required if the attacker controls the attached USB device. In CVSS terms this aligns better with physical attack surface than local-user execution. USB redirection in virtualization, test labs, kiosks, docking stations, or systems accepting untrusted peripherals can make the attack more practical.

Namespaces and containers generally do not make this directly reachable unless the environment delegates USB device attachment, USB/IP, VFIO, or similar hardware redirection to less trusted users.

Call-site confidence: high. The patch and commit message directly show the failing probe path and the later disconnect consequence.

## 4. Severity interpretation

This is more than an ordinary Moderate because the commit explicitly identifies kernel use-after-free and double-free. However, the conservative score remains below Important because exploitation depends on physical or emulated USB device control, a specific registration-failure path, and there is no demonstrated reclaim, arbitrary write, callback control, or type confusion primitive.

Realistic impact is kernel crash / denial of service. Theoretical impact could include privilege escalation or broader memory corruption consequences, but that remains unproven from the provided patch. This should therefore be handled as Actionable Moderate at minimum, with manual review due to the UAF/double-free class.

## 5. One-sentence report phrase

A btusb probe error path can leave sibling USB interfaces bound to freed driver state after hci_register_dev() failure, causing use-after-free or double-free on later disconnect and requiring manual review because the issue is kernel lifetime corruption reachable through malicious or faulty USB device behavior.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED.

Reason: explicit UAF and double-free in a kernel device lifetime path, even though reachability is physical/USB-mediated and no strong LPE primitive is demonstrated.

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

Patch: Bluetooth: btusb: fix use-after-free on registration failure
Commit: e09ac7d0c6859a360bf36e7104aef03f88184e0b
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=e09ac7d0c6859a360bf36e7104aef03f88184e0b

Commit description:

Make sure to release the sibling interfaces in case controller
registration fails to avoid use-after-free and double-free when they are
eventually disconnected.

This issue was reported by Sashiko while reviewing a fix for a wakeup
source leak in the btusb probe errors paths.

Link: https://sashiko.dev/#/patchset/20260402092704.2346710-1-johan%40kernel.org
Fixes: 9bfa35f ("[Bluetooth] Add SCO support to btusb driver")
Fixes: 9d08f50 ("Bluetooth: btusb: Add support for Broadcom LM_DIAG interface")
Cc: stable@vger.kernel.org	# 2.6.27
Reviewed-by: Paul Menzel <pmenzel@molgen.mpg.de>
Signed-off-by: Johan Hovold <johan@kernel.org>
Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  drivers/bluetooth/btusb.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=e09ac7d0c6859a360bf36e7104aef03f88184e0b

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

The original Linux kernel CVE announcement for CVE-2026-64471 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64471

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:H/PR:N/UI:R/S:U/C:L/I:L/A:H
  The Best / paranoid CVSS vector: AV:P/AC:H/PR:N/UI:R/S:U/C:H/I:H/A:H
  The Best / paranoid CVSS score: 6.3

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).