[CVE-2026-52918][MODERATE 7.0] Bluetooth: serialize accept_q access [ Upstream

[CVE-2026-52918][MODERATE 7.0] Bluetooth: serialize accept_q access [ Upstream

[AL-KERNEL]

CVE: CVE-2026-52918
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: Bluetooth: serialize accept_q access [ Upstream
Commit: d9ce4de05df2385c19e2c7d12f529144e1a44af1
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=d9ce4de05df2385c19e2c7d12f529144e1a44af1
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-52918
Analysis date: Wed, 24 Jun 2026 04:30:02 -0400
ActionableScore: 5
ActionableScore lower bound: 4
Actionable bucket: Strong Important candidate / Actionable Moderate at minimum
Manual review required: YES

Summary:
A race in Bluetooth accept queue handling can allow poll or accept dequeue paths to observe a child socket while teardown concurrently unlinks it and drops the last reference, creating a kernel use-after-free candidate that can cause DoS and warrants manual review for stronger impact.

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

The original Linux kernel CVE announcement for CVE-2026-52918 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-52918

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-2026-52918	MODERATE	CHECK	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:A/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H';CWE-362;*CWE-416;CWE-667;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:H';BEST CVSS score: '7.5';DESCR 'A race in Bluetooth accept queue handling can allow bt_sock_poll() or the accept dequeue path to observe a child socket while teardown concurrently unlinks it and drops the last reference. This is a use-after-free candidate in kernel socket lifetime management and can cause at least a kernel crash. For the CVSS the PR:N is used for the paranoid adjacent scenario because an attacker may only need Bluetooth radio adjacency to interact with a listening Bluetooth service and force child connection teardown while the service polls the accept queue. The issue is not Internet reachable in the usual sense and normally requires local Bluetooth availability or proximity to the target device. Impact is at least denial of service and in the worst case may allow confidentiality or integrity impact due to kernel use-after-free behavior.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 5)	YES	REMOTE LOCK DANGER INIT NETWORK KPANIC  KPANIC INCREASED_TO_HIGH_BASED_ON_GUESSCVSS KPANIC DECREASED_TO_MODERATE70_BASED_ON_ACTIONABLESCORELOWERTHAN7	NO	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: **Strong Important candidate / Actionable Moderate at minimum**::

## 2. Signal breakdown

Conservative signals:

* Local unprivileged trigger: +1. A local user or process able to use Bluetooth sockets can exercise accept and poll paths.
* Memory corruption, weak race UAF primitive: +1. The patch fixes unsynchronized accept_q traversal where a child socket can be unlinked and its last reference dropped concurrently.
* Real lifetime corruption: +1. The bug is explicitly a socket lifetime and reference handling race involving sock_put and child teardown.
* Reliable kernel crash / strong DoS: +1. A stale struct sock during poll or accept dequeue can plausibly lead to kernel crash.
* Hard or unreliable race / special timing required: -1. Exploitation depends on timing between poll or accept dequeue and child teardown.
* Broad/common subsystem exposure: +1. Bluetooth is a widely supported kernel subsystem, though not always enabled or reachable on server systems.

Paranoid additional interpretation:

* Remote reachable / adjacent network-triggerable: +2 instead of local-only reachability. A nearby Bluetooth peer may influence connection creation and teardown against a listening Bluetooth service.
* Race-UAF cap applied. Because the patch does not show attacker-controlled reclaim, write-after-free, callback dispatch, type confusion, or refcount takeover, the paranoid score is capped at 5.

Not awarded:

* Strong LPE plausibility: +0. The patch supports a UAF candidate but does not demonstrate controlled reclaim, controlled overwrite, stale callback use, or type confusion.
* Confidentiality and integrity impact bonuses: +0 for conservative scoring. They remain theoretical only.
* Dirty-Pipe-like or page-cache primitive: +0. Not applicable.

## 3. Reachability analysis

The direct trigger is local use of Bluetooth socket APIs combined with accept queue polling and concurrent child socket teardown. In typical local scoring this is PR:L because a local process must interact with the Bluetooth socket interface.

The paranoid interpretation is AV:A and PR:N in CVSS-like terms, because a Bluetooth-adjacent attacker may be able to interact with a listening Bluetooth service and influence child connection teardown while the local service polls the accept queue. This is not Internet-reachable in the normal TCP/IP sense and requires Bluetooth availability, radio proximity, and a suitable listening service or socket state.

Namespaces do not strongly reduce risk here because the affected lifetime bug is in the shared kernel Bluetooth stack. Practical exploitability still depends on whether Bluetooth is enabled, whether untrusted users or nearby peers can reach a listening Bluetooth profile, and whether the race is reproducible.

## 4. Severity interpretation

This is not an ordinary low-risk Moderate because the patch fixes a real unsynchronized list and socket lifetime race with possible use-after-free. It is also not a clearly demonstrated Important-class LPE because no controlled reclaim, write primitive, callback control, or type confusion is shown.

The most defensible conservative interpretation is borderline/actionable Moderate. The paranoid interpretation reaches Actionable Moderate and possible Important-candidate handling because Bluetooth adjacency may remove local privilege requirements and UAF lifetime bugs have historically been underestimated.

## 5. One-sentence report phrase

A race in Bluetooth accept queue handling can allow poll or accept dequeue paths to observe a child socket while teardown concurrently unlinks it and drops the last reference, creating a kernel use-after-free candidate that can cause DoS and warrants manual review for stronger impact.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

Reason: this is a race-based UAF candidate in kernel socket lifetime management. Even though the patch does not prove privilege escalation, the combination of Bluetooth reachability, stale socket references, and lifetime corruption should not be auto-closed.

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

Patch: Bluetooth: serialize accept_q access [ Upstream
Commit: d9ce4de05df2385c19e2c7d12f529144e1a44af1
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=d9ce4de05df2385c19e2c7d12f529144e1a44af1

Changed files:
  include/net/bluetooth/bluetooth.h
  net/bluetooth/af_bluetooth.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=d9ce4de05df2385c19e2c7d12f529144e1a44af1

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

The original Linux kernel CVE announcement for CVE-2026-52918 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-52918

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:L/UI:N/S:U/C:L/I:L/A:H
  The Best / paranoid CVSS vector: AV:A/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H
  The Best / paranoid CVSS score: 7.5

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: 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).