[CVE-2026-63974][LOW] Bluetooth: hci_sync: Set HCI_CMD_DRAIN_WORKQUEUE during device close [ Upstream

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

CVE: CVE-2026-63974
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: Bluetooth: hci_sync: Set HCI_CMD_DRAIN_WORKQUEUE during device close [ Upstream
Commit: 9cebe4680bb9a72f80c6541eb24af06db7a1fbc9
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=9cebe4680bb9a72f80c6541eb24af06db7a1fbc9
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-63974
Analysis date: Sun, 19 Jul 2026 14:11:39 -0400
ActionableScore: 2
ActionableScore lower bound: 0
Actionable bucket: Ordinary Moderate / Low-like
Manual review required: NO

Summary:
Bluetooth HCI close/reset handling could allow command timeout work to be queued while the device workqueue is being drained, causing a local availability issue in the Bluetooth subsystem, with no concrete memory corruption or privilege escalation primitive shown.

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ABOUT THIS REPORT
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The original Linux kernel CVE announcement for CVE-2026-63974 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-63974

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-2026-63974	LOW	CHECK WITH IMPACT FROM ORIG NN MODERATE	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-362;CWE-667;CWE-755;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '4.7';DESCR 'Bluetooth HCI device close can run in the reset path while the HCI device workqueue is being drained. Without HCI_CMD_DRAIN_WORKQUEUE, command timeout work may still be queued during that drain window through cmd_timer or command count handling, which can leave the close or reset path in an inconsistent state. For the CVSS the PR:L is used in the paranoid score because some deployments may delegate Bluetooth management or reset capability to a local service, container root, or reduced privilege administrator rather than full host root. The issue is not network reachable in the CVSS sense and requires local control of the Bluetooth device lifecycle. Impact is denial of service through a reset or close hang, workqueue disruption, or Bluetooth subsystem availability loss. No concrete memory corruption primitive is visible from the patch context.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate / Low-like (with actual score 1)	YES	REMOTE INIT SIMPLEFIX NETWORK TIMER HARDWARE  DECREASED_TO_MODERATE_REGULAR_FROM_MODERATE7_BASED_ON_GUESSCVSS_AND_CIANNH DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_ACTIONABLESCORELESSTHAN3	YES	NO	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=2
ActionableScoreLower=0

## 1. ActionableScore

* Conservative score: 0
* Paranoid score: 2
* Final recommended bucket: **Ordinary Moderate / Low-like**

## 2. Signal breakdown

Conservative signals:

* Reliable kernel crash / strong DoS: +0. The patch indicates timeout work could be queued while the HCI workqueue is being drained, but it does not show a concrete kernel crash, UAF, Oops, BUG, or panic path.
* Availability impact realistic: +1. A close/reset hang or Bluetooth subsystem disruption is plausible.
* Hard or unreliable race / special timing required: -1. The issue depends on close/reset overlapping with workqueue drain and timeout queuing.
* Requires admin/root/CAP_NET_ADMIN in typical deployments: -2. Reliable triggering usually requires local control over Bluetooth device close/reset or management paths.
* Broad/default/common subsystem: +0. Bluetooth is common, but the affected path requires Bluetooth hardware/device lifecycle operations and is not a central always-on kernel path.

Paranoid signals:

* Availability impact realistic: +1. In a worse case, the reset/close path may hang or disrupt Bluetooth device availability.
* Broad/default/common subsystem: +1. Bluetooth is broadly deployed on client systems, and management services may expose lifecycle operations indirectly.
* Hard or unreliable race / special timing required: -1.
* Privilege penalty reduced: +0 instead of -2. Some deployments may delegate Bluetooth management to a local service, container root, or reduced-privilege administrator, so the full host-root penalty may be too strict.

No memory-corruption signals apply:

* No UAF, double-free, OOB write, type confusion, refcount takeover, stale callback dispatch, or attacker-controlled reclaim is shown.
* No privilege escalation primitive is supported by the patch.
* No confidentiality or integrity impact is supported.

Call-site confidence: medium. The patch names hci_cmd_work() and handle_cmd_cnt_and_timer(), but the full call-site logic is not included in the provided diff.

## 3. Reachability analysis

The bug is local and tied to Bluetooth HCI device lifecycle handling. A realistic trigger requires the ability to initiate or influence HCI device close/reset while command timeout work may still be queued. In typical deployments this requires administrative Bluetooth management privileges, commonly CAP_NET_ADMIN or a privileged system service. It is not network reachable in the CVSS sense, and ordinary remote Bluetooth traffic alone is not sufficient based on the provided patch. Namespaces or containers could matter only if Bluetooth management is delegated to a reduced-privilege context.

## 4. Severity interpretation

This behaves like an ordinary Moderate or Low-like availability bug, not an Important-class vulnerability. The theoretical issue is a workqueue lifecycle race during device close/reset, but the patch does not support memory corruption, privilege escalation, or information disclosure. The realistic impact is Bluetooth subsystem DoS or reset/close disruption.

## 5. One-sentence report phrase

Bluetooth HCI close/reset handling could allow command timeout work to be queued while the device workqueue is being drained, causing a local availability issue in the Bluetooth subsystem, with no concrete memory corruption or privilege escalation primitive shown.

## 6. Manual review recommendation

NO MANUAL CHECK NEEDED

Reason: the patch shows a local privileged workqueue-drain race with plausible DoS impact only, no network reachability, and no concrete memory corruption or security-boundary bypass.

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

Patch: Bluetooth: hci_sync: Set HCI_CMD_DRAIN_WORKQUEUE during device close [ Upstream
Commit: 9cebe4680bb9a72f80c6541eb24af06db7a1fbc9
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=9cebe4680bb9a72f80c6541eb24af06db7a1fbc9

Changed files:
  net/bluetooth/hci_sync.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=9cebe4680bb9a72f80c6541eb24af06db7a1fbc9

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

The original Linux kernel CVE announcement for CVE-2026-63974 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-63974

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: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: 0
  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).