[CVE-2026-63944][MODERATE 7.0] Bluetooth: hci_sync: fix UAF in hci_le_create_cis_sync [ Upstream

[CVE-2026-63944][MODERATE 7.0] Bluetooth: hci_sync: fix UAF in hci_le_create_cis_sync [ Upstream

[AL-KERNEL]

CVE: CVE-2026-63944
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: Bluetooth: hci_sync: fix UAF in hci_le_create_cis_sync [ Upstream
Commit: a55618c0f4cead9e59c63f5ee030d393fd70d861
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=a55618c0f4cead9e59c63f5ee030d393fd70d861
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-63944
Analysis date: Sun, 19 Jul 2026 17:01:59 -0400
ActionableScore: 5
ActionableScore lower bound: 4
Actionable bucket: Actionable Moderate at minimum
Manual review required: YES

Summary:
A race in Bluetooth `hci_le_create_cis_sync()` can dereference a freed `hci_conn` after RCU and device locks are released, allowing a nearby Bluetooth peer under specific LE CIS timing conditions to trigger a UAF read and potential kernel DoS.

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

The original Linux kernel CVE announcement for CVE-2026-63944 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-63944

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-2026-63944	MODERATE	CHECK WITH IMPACT FROM ORIG NN IMPORTANT	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:A/AC:H/PR:N/UI:R/S:U/C:N/I:N/A:H';BEST CVSS score: '6.4';DESCR 'A UAF read can occur in Bluetooth hci_le_create_cis_sync because conn_timeout is read through a hci_conn pointer after both RCU protection and the hci_dev lock have been released. A concurrent Bluetooth disconnect can free the hci_conn object in this window, leaving a stale pointer that is later dereferenced while creating an LE CIS command. For the CVSS the PR:N is used for the paranoid score because a nearby Bluetooth peer may influence disconnect timing without local privileges on the victim once the relevant Bluetooth connection state exists. The issue is adjacent network reachable over Bluetooth rather than Internet reachable. Impact is at least denial of service via kernel crash or warning, and in the paranoid case may allow limited confidentiality or integrity impact due to UAF object reuse risk.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate at minimum (with actual score 5)	YES	REMOTE UAF NETWORK KPANIC  KPANIC LOWERED_FROM_HIGH_BASED_ON_GUESSCVSS 	YES	NO	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=5
ActionableScoreLower=4

## 1. ActionableScore

* Conservative score: 4
* Paranoid score: 5
* Final recommended bucket: **Actionable Moderate at minimum**::

## 2. Signal breakdown

* Remote reachable / network-triggerable: +2
  Bluetooth is adjacent-network reachable. A nearby peer may influence connection and disconnect timing, but this is not Internet-reachable.

* Memory corruption, weak/indirect primitive: +1
  This is a UAF read of `conn->conn_timeout` after RCU and device locks are dropped. The patch does not show attacker-controlled reclaim, write-after-free, callback dispatch, or type confusion.

* Real lifetime corruption: +1
  The stale `hci_conn` pointer can survive a concurrent disconnect/free window.

* Reliable kernel crash / strong DoS: +1
  A UAF read in kernel Bluetooth state can plausibly lead to KASAN reports, warnings, or kernel crash depending on allocator reuse and debug settings.

* Hard or unreliable race / special timing required: -1
  Triggering requires a race between LE CIS creation and concurrent disconnect.

* Paranoid exposure uplift: +1
  Bluetooth is a common client/server subsystem, and adjacent attack surface plus UAF lifetime semantics justify not auto-closing without review.

Race-UAF downgrade applied. No Weak LPE concern is awarded because the patch does not show attacker-controlled reclaim, writable stale access, callback control, type confusion, or refcount takeover. Conservative score is capped in the borderline range and paranoid score is capped at 5.

## 3. Reachability analysis

A nearby Bluetooth peer may be able to influence the relevant connection lifecycle if LE CIS or ISO connection creation is in use. No local account on the victim is necessarily required for the paranoid interpretation, but the attacker must be in Bluetooth radio range and must reach a fairly specific Bluetooth state. The affected path is not a generic Internet-facing network path. Containers and namespaces do not materially lower or raise the privilege requirement because the likely trigger is external Bluetooth interaction, not a local namespaced syscall path. Call-site confidence: high, because the provided diff directly shows the stale dereference replaced by a saved local value.

## 4. Severity interpretation

This behaves above an ordinary Moderate because it is a real kernel lifetime bug in an adjacent-network subsystem. It does not reach a strong Important classification on the available evidence because the stale access is a read of a small timeout field and there is no demonstrated reclaim, overwrite, callback, type confusion, or privilege-escalation primitive. The realistic impact is DoS or warning/crash. The theoretical memory-corruption concern is enough for manual review, but not enough to score as strong LPE.

## 5. One-sentence report phrase

A race in Bluetooth `hci_le_create_cis_sync()` can dereference a freed `hci_conn` after RCU and device locks are released, allowing a nearby Bluetooth peer under specific LE CIS timing conditions to trigger a UAF read and potential kernel DoS.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

Reason: this is a real UAF race in an adjacent-network Bluetooth path. The current evidence supports Actionable Moderate rather than Important, but memory lifetime bugs in remotely influenced kernel protocol code should not be auto-closed.

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

Patch: Bluetooth: hci_sync: fix UAF in hci_le_create_cis_sync [ Upstream
Commit: a55618c0f4cead9e59c63f5ee030d393fd70d861
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=a55618c0f4cead9e59c63f5ee030d393fd70d861

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=a55618c0f4cead9e59c63f5ee030d393fd70d861

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

The original Linux kernel CVE announcement for CVE-2026-63944 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-63944

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:R/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: 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).