[CVE-2026-53251][LOW] Bluetooth: ISO: Fix not releasing hdev reference on iso_conn_big_sync [ Upstream

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

CVE: CVE-2026-53251
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: Bluetooth: ISO: Fix not releasing hdev reference on iso_conn_big_sync [ Upstream
Commit: 4bbec25f47b930101294fd310c627c3f53e9661f
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=4bbec25f47b930101294fd310c627c3f53e9661f
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53251
Analysis date: Thu, 25 Jun 2026 10:04:30 -0400
ActionableScore: 2
ActionableScore lower bound: 1
Actionable bucket: Ordinary Moderate / Low-like
Manual review required: NO

Summary:
A missing `hci_dev_put()` in Bluetooth ISO BIG sync can leak an `hci_dev` reference after `hci_get_route()`, allowing a local user with access to Bluetooth ISO functionality to pin device resources and potentially disrupt Bluetooth cleanup or device unregister.

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

The original Linux kernel CVE announcement for CVE-2026-53251 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53251

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-2026-53251	LOW	CHECK	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H';*CWE-772;CWE-404;*CWE-664;Other CVSS 'AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '5.5';DESCR 'Bluetooth ISO BIG sync leaks a reference to hci_dev because hci_get_route returns a held device and iso_conn_big_sync exits without hci_dev_put. A local process that can reach the Bluetooth ISO socket path and trigger BIG sync can repeatedly leave device references pinned. For the CVSS the PR:L is used for the paranoid score because practical triggering requires local code execution with access to Bluetooth ISO functionality, but not necessarily full administrator control in deployments that expose Bluetooth sockets to users or services. The issue is not network reachable over IP and requires local interaction with the Bluetooth stack and a suitable controller or configuration. Impact is denial of service or device management disruption, such as preventing clean device unregister or keeping resources alive, with no evidence of memory corruption, information disclosure, or privilege escalation.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate / Low-like (with actual score 2)	YES	REMOTE SIMPLEFIX NETWORK  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=1

## 1. ActionableScore

* Conservative score: 1
* Paranoid score: 2
* Final recommended bucket: **Ordinary Moderate / Low-like**::

## 2. Signal breakdown

* Local unprivileged trigger: +1. A local process that can reach the Bluetooth ISO socket path may trigger `iso_conn_big_sync()`.
* Availability impact realistic: +1 in paranoid scoring only. Repeated reference leaks may keep `hci_dev` objects pinned and disrupt Bluetooth device cleanup, unregister, unload, or recovery.
* Rare AND difficult-to-reach subsystem/configuration: -1. Bluetooth ISO BIG sync is not a broad default kernel attack surface and requires suitable Bluetooth ISO functionality and controller state.
* No memory corruption: +0. The patch adds a missing `hci_dev_put()` for a reference obtained through `hci_get_route()` / `hci_dev_hold()`. This is a reference leak, not UAF, double free, OOB write, or type confusion.
* No privilege escalation signal: +0. There is no reclaim, stale callback, overwrite, refcount takeover, or attacker-controlled object reuse shown.
* No confidentiality or integrity signal: +0. The bug does not expose data or modify protected data.

## 3. Reachability analysis

The bug is locally reachable through the Bluetooth ISO path, assuming the attacker can create or operate the relevant Bluetooth ISO socket flow and the system has suitable Bluetooth support. It is not network-reachable over IP. Namespaces may affect access to Bluetooth sockets, but typical exploitation still requires local code execution and access to Bluetooth functionality. The affected feature is not a common always-enabled server-side path.

## 4. Severity interpretation

This behaves like an ordinary Moderate or Low-like resource lifetime bug. The realistic impact is denial of service or device-management disruption through leaked `hci_dev` references. The patch does not support a memory-corruption primitive or privilege escalation path. Even the paranoid interpretation should stay within resource leak / availability impact and should not be upgraded to Important.

## 5. One-sentence report phrase

A missing `hci_dev_put()` in Bluetooth ISO BIG sync can leak an `hci_dev` reference after `hci_get_route()`, allowing a local user with access to Bluetooth ISO functionality to pin device resources and potentially disrupt Bluetooth cleanup or device unregister.

## 6. Manual review recommendation

NO MANUAL CHECK NEEDED

This is a local reference leak without evidence of memory corruption, sensitive object access, privilege escalation, or network reachability.

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

Patch: Bluetooth: ISO: Fix not releasing hdev reference on iso_conn_big_sync [ Upstream
Commit: 4bbec25f47b930101294fd310c627c3f53e9661f
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=4bbec25f47b930101294fd310c627c3f53e9661f

Changed files:
  net/bluetooth/iso.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=4bbec25f47b930101294fd310c627c3f53e9661f

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

The original Linux kernel CVE announcement for CVE-2026-53251 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53251

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:L/PR:L/UI:N/S:U/C:N/I:N/A:L
  The Best / paranoid CVSS vector: AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS score: 5.5

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: 1
  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).