[CVE-2026-64408][MODERATE REGULAR] Bluetooth: bnep: pin L2CAP connection during netdev registration

[CVE-2026-64408][MODERATE REGULAR] Bluetooth: bnep: pin L2CAP connection during netdev registration

[AL-KERNEL]

CVE: CVE-2026-64408
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: Bluetooth: bnep: pin L2CAP connection during netdev registration
Commit: 390b5db3ff8745187f094c4e915663b7b1f98944
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=390b5db3ff8745187f094c4e915663b7b1f98944
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64408
Analysis date: Sat, 25 Jul 2026 07:44:33 -0400
ActionableScore: 4
ActionableScore lower bound: 2
Actionable bucket: Borderline. Manual review recommended. Actionable Moderate if adjacent triggering is confirmed
Manual review required: YES

Summary:
Bluetooth BNEP netdev registration can race with L2CAP connection teardown, leaving `register_netdev()` to use a freed parent HCI device and causing a kernel crash, with manual review recommended because this is a real lifetime UAF candidate but no strong LPE primitive is shown.

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

The original Linux kernel CVE announcement for CVE-2026-64408 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64408

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: 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
======================================================================

CVE-2026-64408	MODERATE	CHECK WITH IMPACT FROM ORIG NN MODERATE	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:A/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:H';*CWE-416;CWE-362;CWE-667;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '6.4';DESCR 'Bluetooth BNEP netdev registration can race with L2CAP connection teardown because bnep_add_connection used the channel connection without holding a lock or taking a reference. If controller teardown clears and releases the L2CAP connection while register_netdev() is using the HCI parent device, the registration path can dereference a freed parent device. This is a race condition and use-after-free candidate, so impact is at least denial of service via kernel crash and in worst case may allow limited confidentiality or integrity impact from memory corruption. For the CVSS the PR:N is used in the paranoid score because a Bluetooth adjacent peer may be able to influence connection setup and teardown through the BNEP/L2CAP protocol while the vulnerable host performs netdev registration. The issue is not Internet reachable, but it may be reachable from Bluetooth radio range or from a local process that can create BNEP connections.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline. Manual review recommended. Actionable Moderate if adjacent triggering is confirmed (with actual score 3)	YES	REMOTE DANGER UAF NETWORK HARDWARE SYZBOT  DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5	NO	NO	checked

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

ActionableScore=4
ActionableScoreLower=2

## 1. ActionableScore

* Conservative score: 2
* Paranoid score: 4
* Final recommended bucket: **Borderline. Manual review recommended. Actionable Moderate if adjacent triggering is confirmed**

## 2. Signal breakdown

* Memory corruption, weak or indirect corruption candidate: +1
  The patch fixes a stale lifetime window where `conn->hcon->dev` may be used after the L2CAP connection is cleared and released.
* Real lifetime corruption: +1
  The fix explicitly pins `struct l2cap_conn` with `l2cap_conn_get()` under `l2cap_chan_lock()` and releases it after `register_netdev()`.
* Reliable kernel crash / strong DoS: +1
  Dereferencing a freed parent device during netdev registration is a credible kernel crash path.
* Remote reachable / adjacent Bluetooth influence in paranoid interpretation: +2
  A Bluetooth peer may influence L2CAP/BNEP connection setup or teardown timing, but this is not Internet reachable.
* Hard or unreliable race / special timing required: -1
  The issue depends on concurrent BNEP netdev registration and controller or L2CAP teardown.
* Requires admin/root/CAP_NET_ADMIN in typical deployments: -2 for conservative score
  Creating BNEP netdevs is usually done by privileged Bluetooth control plane code or a process with network administration privileges.
* Race-UAF downgrade rule applied
  No attacker-controlled reclaim, stale callback dispatch, type confusion, refcount takeover, or write-after-free primitive is shown, so this is not scored as strong LPE.

Call-site confidence: high. The relevant call to `SET_NETDEV_DEV()` and `register_netdev()` is visible in the patch.

## 3. Reachability analysis

Conservatively, the trigger requires local privileged control over BNEP connection setup, usually through a Bluetooth daemon or CAP_NET_ADMIN-equivalent path. In containerized or reduced-capability environments, privileges may be lower if Bluetooth or netdev management is delegated, but that is not the normal default.

Paranoid reachability is Bluetooth-adjacent rather than Internet-remote. A nearby peer may be able to influence L2CAP/BNEP connection lifetime while the vulnerable host performs registration, but the local host still appears to participate in creating the BNEP netdev. The subsystem is not a core default network packet path, but Bluetooth is common enough that this should not be dismissed as purely theoretical.

## 4. Severity interpretation

This behaves more like a borderline actionable Moderate than an ordinary low-priority cleanup. The bug is a real lifetime race and UAF candidate in a kernel netdev registration path, but the patch does not show a strong exploitation primitive such as controlled reclaim, arbitrary write, callback control, or type confusion.

The realistic impact is kernel crash / DoS. Theoretical privilege escalation cannot be fully ruled out because UAF bugs sometimes become exploitable, but the evidence here supports weak memory-corruption concern rather than Important-class treatment by default.

## 5. One-sentence report phrase

Bluetooth BNEP netdev registration can race with L2CAP connection teardown, leaving `register_netdev()` to use a freed parent HCI device and causing a kernel crash, with manual review recommended because this is a real lifetime UAF candidate but no strong LPE primitive is shown.

## 6. Manual review recommendation

MANUAL CHECK RECOMMENDED

Reason: the patch fixes a real refcount/lifetime race around a freed kernel device object, but exploitation beyond DoS is not demonstrated and the main trigger likely requires privileged local Bluetooth control unless adjacent peer influence is confirmed.

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

Patch: Bluetooth: bnep: pin L2CAP connection during netdev registration
Commit: 390b5db3ff8745187f094c4e915663b7b1f98944
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=390b5db3ff8745187f094c4e915663b7b1f98944

Commit description:

bnep_add_connection() reads the L2CAP connection without holding the
channel lock, then passes its HCI device to register_netdev(). Controller
teardown can clear and release that connection concurrently, leaving the
network device registration path to dereference a freed parent device.

Take a reference to the L2CAP connection while holding the channel lock.
Retain it until register_netdev() has taken the parent device reference.

Fixes: 65f53e9 ("Bluetooth: Access BNEP session addresses through L2CAP channel")
Reported-by: syzbot+fed5dce4553262f3b35c@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=fed5dce4553262f3b35c
Cc: stable@vger.kernel.org
Signed-off-by: Yousef Alhouseen <alhouseenyousef@gmail.com>
Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  net/bluetooth/bnep/core.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=390b5db3ff8745187f094c4e915663b7b1f98944

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

The original Linux kernel CVE announcement for CVE-2026-64408 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64408

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:H/UI:N/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS vector: AV:A/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:H
  The Best / paranoid CVSS score: 6.4

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: 2
  Paranoid ActionableScore: 4

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).