[CVE-2026-68085][MODERATE 7.0] Bluetooth: hci_uart: clear HCI_UART_SENDING when write_work is canceled

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

CVE: CVE-2026-68085
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: Bluetooth: hci_uart: clear HCI_UART_SENDING when write_work is canceled
Commit: d52446b3e735cfdbdc2a58342163803bc2e64249
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=d52446b3e735cfdbdc2a58342163803bc2e64249
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-68085
Analysis date: Mon, 10 Aug 2026 14:39:21 -0400
ActionableScore: 5
ActionableScore lower bound: 3
Actionable bucket: Strong Important candidate / Actionable Moderate at minimum
Manual review required: YES

Summary:
A race in Bluetooth hci_uart close and flush handling can leave TX work state inconsistent and may allow stale access to tx_skb, causing persistent local Bluetooth TX DoS and requiring review for possible UAF impact.

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ABOUT THIS REPORT
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The original Linux kernel CVE announcement for CVE-2026-68085 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-68085

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.

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AL-KERNEL CLASSIFICATION RESULT
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CVE-2026-68085	MODERATE	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:H/I:H/A:H';CWE-362;*CWE-416;CWE-667;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '7';DESCR 'Bluetooth hci_uart can leave HCI_UART_SENDING set when pending write_work is canceled during close, which can block future TX after the device is reopened. The same path also clears tx_skb during flush while write_work may otherwise be active, making this a race and possible use-after-free candidate around the UART TX state. For the CVSS the PR:L is used for the paranoid score because a local user or service with access to Bluetooth HCI UART control or the backing tty may be able to trigger close reopen or flush paths without full host administrator privileges. The issue is not directly network reachable and requires local interaction with the Bluetooth UART control path. Impact is at least local denial of service through a stuck TX path or kernel crash, and in the worst case may allow confidentiality or integrity impact if the tx_skb race is exploitable as memory corruption.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 4)  SKIP CVE-2026-68085 UNKNOWN SKIP The Fixes patch not applied yet, so unlikely that actual: c1bb9336ae6b54a5f6a353c4bd4ed9a4307e429b YES  NO NO unknown 	MAYBE	DANGER RACE UAF HARDWARE  DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5	-	-	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=5
ActionableScoreLower=3

## 1. ActionableScore

* Conservative score: 3
* Paranoid score: 5
* Final recommended bucket: **Strong Important candidate / Actionable Moderate at minimum**::

## 2. Signal breakdown

Conservative signals:

* Memory corruption, weak or indirect corruption candidate: +1. The patch explicitly changes workqueue synchronization before freeing `tx_skb`, which suggests a possible stale skb access, but no controlled reclaim or overwrite primitive is shown.
* Real lifetime corruption: +1. `tx_skb` lifetime is protected by switching from `cancel_work_sync()` to `disable_work_sync()` during flush.
* Reliable local DoS: +1. Leaving `HCI_UART_SENDING` set can block future TX after reopen.
* Availability impact realistic: +1. The TX stall can persist across close and reopen until the state is corrected.
* Hard or unreliable race / special timing: -1. The dangerous part depends on pending or concurrently queued `write_work`.
* Requires privileged or delegated device access in typical deployments: -1. Triggering close, reopen, or flush usually requires Bluetooth HCI UART control, tty access, or a privileged service context, but not necessarily full host-root in all deployments.

Conservative total: 3

Paranoid additional interpretation:

* Local lower-privilege trigger: +1. In some systems Bluetooth or backing tty access may be delegated to a service, reduced-capability root, container-like environment, or local user group.
* Weak LPE concern remains limited. No extra LPE bonus is awarded because the patch does not show attacker-controlled reclaim, type confusion, callback control, refcount takeover, or arbitrary write.
* Race-UAF downgrade rule applies. Treat as weak memory corruption candidate and cap paranoid handling at 5.

Paranoid total: 5

## 3. Reachability analysis

The issue is not network reachable. It is triggered through local Bluetooth HCI UART lifecycle paths such as close, reopen, flush, or TX wakeup handling.

In typical deployments, direct triggering requires elevated privileges, device ownership, CAP_NET_ADMIN-like Bluetooth management rights, or control through a privileged Bluetooth service. Namespace or container setups may reduce the practical privilege boundary if a container, service account, or delegated user can control the HCI UART device or backing tty.

The path is relevant only on systems using Bluetooth HCI over UART. It is common on some laptops, embedded boards, phones, and IoT devices, but not a universal server default.

Call-site confidence: medium. The patch includes `hci_uart_flush()` and `hci_uart_close()` and clearly shows the affected lifetime transition, but the full `write_work` body is not included.

## 4. Severity interpretation

This behaves above an ordinary Moderate if the `tx_skb` race can be confirmed as a real stale access or UAF. Realistically, the directly demonstrated impact is local Bluetooth TX denial of service caused by a stuck `HCI_UART_SENDING` state.

The theoretical memory corruption concern is based on the need to disable `write_work` before clearing and freeing `tx_skb`. However, the patch does not demonstrate attacker-controlled reuse, writable stale access, callback control, or a concrete privilege escalation primitive. Therefore, conservative triage is borderline Moderate, while paranoid triage reaches Actionable Moderate and should not be auto-closed without manual review.

## 5. One-sentence report phrase

A race in Bluetooth hci_uart close and flush handling can leave TX work state inconsistent and may allow stale access to tx_skb, causing persistent local Bluetooth TX DoS and requiring review for possible UAF impact.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

Reason: the patch touches workqueue synchronization and skb lifetime around `tx_skb`, and the fixed area is adjacent to prior UAF and race fixes. The proven impact may only be local DoS, but the lifetime pattern is sensitive enough to require manual source review.

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

Patch: Bluetooth: hci_uart: clear HCI_UART_SENDING when write_work is canceled
Commit: d52446b3e735cfdbdc2a58342163803bc2e64249
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=d52446b3e735cfdbdc2a58342163803bc2e64249

Commit description:

HCI_UART_SENDING bit in tx_state means write_work is pending and blocks
queueing it again.  Currently this bit is not cleared when canceling the
work in hci_uart_close(), which blocks future writes when device is
reopened later if write_work was pending.

Fix by clearing HCI_UART_SENDING when canceling the work.

Also make clearing of tx_skb safe by using disable_work_sync +
enable_work instead of just cancel_work_sync.  hci_uart_flush() purges
the proto tx queue so we can cancel the pending write_work there,
instead of doing it just in hci_uart_close().  Re-enable and possibly
requeue the work after queue flush.

Fixes: c1bb933 ("Bluetooth: hci_uart: fix UAFs and race conditions in close and init paths")
Link: https://lore.kernel.org/linux-bluetooth/07e0a28650773abec711ee492fdb1bf5d21a6c98.camel@iki.fi/
Cc: stable@vger.kernel.org
Signed-off-by: Pauli Virtanen <pav@iki.fi>
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/hci_ldisc.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=d52446b3e735cfdbdc2a58342163803bc2e64249

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

The original Linux kernel CVE announcement for CVE-2026-68085 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-68085

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:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H
  The Best / paranoid CVSS score: 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: 3
  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: NO
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).