[CVE-2026-64206][MODERATE REGULAR] Bluetooth: L2CAP: cancel pending_rx_work before taking conn->lock

[CVE-2026-64206][MODERATE REGULAR] Bluetooth: L2CAP: cancel pending_rx_work before taking conn->lock

[AL-KERNEL]

CVE: CVE-2026-64206
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: Bluetooth: L2CAP: cancel pending_rx_work before taking conn->lock
Commit: d5616beb3355b5fca2280d796c1cf7ada4ee6551
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=d5616beb3355b5fca2280d796c1cf7ada4ee6551
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64206
Analysis date: Mon, 20 Jul 2026 13:11:13 -0400
ActionableScore: 4
ActionableScore lower bound: 3
Actionable bucket: Borderline, manual review recommended / Actionable Moderate if Bluetooth is exposed
Manual review required: YES

Summary:
A Bluetooth L2CAP teardown deadlock can occur when `l2cap_conn_del()` waits for `pending_rx_work` while holding `conn->lock`, allowing an adjacent Bluetooth peer to potentially trigger a denial of service without local privileges.

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

The original Linux kernel CVE announcement for CVE-2026-64206 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64206

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.

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

CVE-2026-64206	MODERATE	CHECK WITH IMPACT FROM ORIG NN MODERATE	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:A/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H';CWE-667;*CWE-833;CWE-362;Other CVSS 'AV:A/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '6.5';DESCR 'Bluetooth L2CAP connection teardown can deadlock because l2cap_conn_del holds conn lock while waiting for pending_rx_work to finish, while process_pending_rx also needs the same conn lock. A nearby Bluetooth peer may be able to exercise the receive work submit path and the disconnect or teardown path, causing a stuck teardown and denial of service in the Bluetooth stack. For the CVSS the PR:N is used because the attacker does not need local code execution on the victim when the vulnerable Bluetooth path is reachable over the adjacent Bluetooth radio interface. The issue is not Internet reachable and requires Bluetooth adjacency or access to the local Bluetooth network context. Impact is denial of service only, with no supported evidence of memory corruption, information disclosure, or privilege escalation.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline, manual review recommended / Actionable Moderate if Bluetooth is exposed (with actual score 4)	YES	REMOTE LOCK DEADLOCK INIT NETWORK  DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5	NO	NO	checked

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

ActionableScore=4
ActionableScoreLower=3

## 1. ActionableScore

* Conservative score: 3
* Paranoid score: 4
* Final recommended bucket: **Borderline, manual review recommended / Actionable Moderate if Bluetooth is exposed**::

## 2. Signal breakdown

Conservative signals:

* Adjacent network-triggerable Bluetooth path: +2. A nearby Bluetooth peer may influence L2CAP receive and disconnect paths. This is not Internet-reachable, but it is externally reachable over Bluetooth adjacency.
* Reliable kernel deadlock / strong DoS: +1. The patch fixes a lock-before-drain deadlock between `l2cap_conn_del()` and `process_pending_rx()`.
* Broad/common subsystem exposure: +1. Bluetooth is common on client systems, though not always enabled on servers.
* Hard timing / interleaving required: -1. The issue depends on `pending_rx_work` being queued or running while teardown drains it.

Paranoid difference:

* Timing penalty not applied: +1 relative to conservative. The described submit path, teardown path, and worker lock edge suggest the deadlock may be reproducible once the L2CAP state is exercised.

No memory-corruption signals apply. No UAF, OOB write, double-free, type confusion, stale callback control, refcount takeover, information leak, or privilege-escalation primitive is shown.

Call-site confidence: high. The relevant queue, cancel, worker, and mutex paths are all described in the commit and visible in the patch context.

## 3. Reachability analysis

The likely attacker is a nearby Bluetooth peer able to interact with the L2CAP connection lifecycle. No local code execution on the victim is required if the Bluetooth interface is discoverable or otherwise reachable. This is best treated as adjacent-network reachability, not Internet remote reachability.

Namespaces and containers do not materially lower or raise the main attack condition because the interesting path is the host Bluetooth stack and radio exposure. The path is common on systems with Bluetooth enabled, especially desktops, laptops, embedded devices, and phones, but often absent or disabled on servers.

Realistic exploitation requires Bluetooth adjacency and a sequence that causes pending receive work to exist while connection teardown runs. The demonstrated lockdep cycle supports a real DoS concern, but the impact remains availability-only.

## 4. Severity interpretation

This behaves more like an actionable Moderate or borderline manual-review issue, not an Important-class vulnerability. The practical impact is a Bluetooth stack or kernel worker deadlock causing denial of service. There is no supported evidence of memory corruption, confidentiality impact, integrity impact, or privilege escalation.

The paranoid score is higher only because Bluetooth adjacency can be attacker-controlled and the deadlock may be reproducible. It should not be upgraded beyond DoS because the patch only changes work cancellation ordering and does not indicate a memory lifetime or overwrite primitive.

## 5. One-sentence report phrase

A Bluetooth L2CAP teardown deadlock can occur when `l2cap_conn_del()` waits for `pending_rx_work` while holding `conn->lock`, allowing an adjacent Bluetooth peer to potentially trigger a denial of service without local privileges.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

Reason: the bug is externally reachable over an adjacent Bluetooth attack surface and affects kernel availability, even though it is DoS-only and does not currently show memory corruption or privilege-escalation potential.

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

Patch: Bluetooth: L2CAP: cancel pending_rx_work before taking conn->lock
Commit: d5616beb3355b5fca2280d796c1cf7ada4ee6551
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=d5616beb3355b5fca2280d796c1cf7ada4ee6551

Commit description:

l2cap_conn_del() takes conn->lock and then calls cancel_work_sync() for
pending_rx_work.  process_pending_rx() takes the same mutex, so teardown
can deadlock against the worker it is flushing.

This issue was found by our static analysis tool and then manually
reviewed against the current tree.

The grounded PoC kept the l2cap_conn_ready() -> queue_work(...,
&conn->pending_rx_work) submit path, the l2cap_conn_del() ->
cancel_work_sync(&conn->pending_rx_work) teardown path, and the
process_pending_rx() -> mutex_lock(&conn->lock) worker edge.  Lockdep
reported:

  WARNING: possible circular locking dependency detected
  process_pending_rx+0x21/0x2a [vuln_msv]
  l2cap_conn_del.constprop.0+0x3f/0x4e [vuln_msv]
  *** DEADLOCK ***

Cancel pending_rx_work before taking conn->lock, matching the existing
lock-before-drain ordering used for the two delayed works in the same
teardown path.  The pending_rx queue is still purged after the work has
been cancelled and conn->lock has been acquired.

Fixes: 7ab56c3 ("Bluetooth: Fix deadlock in l2cap_conn_del()")
Cc: stable@vger.kernel.org
Signed-off-by: Runyu Xiao <runyu.xiao@seu.edu.cn>
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/l2cap_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=d5616beb3355b5fca2280d796c1cf7ada4ee6551

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

The original Linux kernel CVE announcement for CVE-2026-64206 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64206

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:A/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS vector: AV:A/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS score: 6.5

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: 3
  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).