[CVE-2026-74530][MODERATE 7.0] Bluetooth: hci_sync: hold conn in hci_connect_big_sync() callback [ Upstream

[CVE-2026-74530][MODERATE 7.0] Bluetooth: hci_sync: hold conn in hci_connect_big_sync() callback [ Upstream

[AL-KERNEL]

CVE: CVE-2026-74530
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: Bluetooth: hci_sync: hold conn in hci_connect_big_sync() callback [ Upstream
Commit: 2d91e6244b69d752503b2d44020d8b0e323dbd38
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=2d91e6244b69d752503b2d44020d8b0e323dbd38
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74530
Analysis date: Sat, 15 Aug 2026 11:26:18 -0400
ActionableScore: 5
ActionableScore lower bound: 3
Actionable bucket: Actionable Moderate at minimum
Manual review required: YES

Summary:
A theoretical use-after-free in Bluetooth BIG Create Sync handling can occur because an asynchronous hci_sync callback used a raw hci_conn pointer without holding a reference, allowing an adjacent Bluetooth-triggered race to cause stale object access and possible kernel crash.

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

The original Linux kernel CVE announcement for CVE-2026-74530 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74530

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
======================================================================

CVE-2026-74530	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:H/I:H/A:H';*CWE-416;CWE-362;CWE-825;Other CVSS 'AV:A/AC:H/PR:N/UI:R/S:U/C:N/I:N/A:H';BEST CVSS score: '7.5';DESCR 'A theoretical use after free exists in the Bluetooth hci_sync BIG Create Sync path because hci_connect_big_sync queued an asynchronous callback with a raw hci_conn pointer without holding a reference. If the connection is freed while the hci_sync task is still pending or running, create_big_complete can later operate on stale conn state and touch conn flags. For the CVSS the PR:N is used for the paranoid score because an adjacent Bluetooth peer may not need privileges on the target once the relevant Bluetooth LE audio sync workflow is reachable. The base impact is denial of service through kernel crash. For the paranoid score, choose the highest still defensible interpretation supported by the UAF bug class and patch context, with preference for manual review sensitivity over autoclosed false negatives. Impact may include confidentiality and integrity in worst case because this is a UAF candidate, not only a NULL dereference or resource leak.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate at minimum (with actual score 4)	YES	REMOTE UAF NETWORK  DECREASED_TO_MODERATE70_BASED_ON_ACTIONABLESCORELOWERTHAN6 DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5	YES	NO	checked

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ACTIONABLESCORE ANALYSIS
======================================================================

ActionableScore=5
ActionableScoreLower=3

## 1. ActionableScore

* Conservative score: 3
* Paranoid score: 5
* Final recommended bucket: **Actionable Moderate at minimum**::

## 2. Signal breakdown

Conservative score:

* Adjacent wireless / network-triggerable path: +2. Bluetooth is not Internet-routable, but an attacker in Bluetooth range may influence the affected connection workflow.
* Memory corruption, weak/indirect corruption candidate: +1. The patch fixes a theoretical UAF of `struct hci_conn`, but no controlled reclaim, type confusion, arbitrary write, or exploit primitive is shown.
* Real lifetime corruption: +1. The bug is a missing reference hold across an asynchronous `hci_sync` callback.
* Hard or unreliable race / special timing required: -1. The issue requires `conn` to be freed while the queued sync task or callback is still pending or running.

Paranoid additional signals:

* Reliable kernel crash / strong DoS: +1. A stale `hci_conn` pointer may be dereferenced and used in `clear_bit()` on `conn->flags`, making kernel crash plausible.
* Weak LPE concern: +1. Because this is a real UAF involving an async callback and stale object access, manual review should not auto-close possible confidentiality or integrity impact, although no concrete reclaim primitive is demonstrated.

## 3. Reachability analysis

The likely external attacker model is an adjacent Bluetooth peer, not a remote IP network attacker. The affected path is in Bluetooth LE BIG Create Sync handling, so realistic triggering depends on Bluetooth being enabled and the relevant LE audio or BIG synchronization workflow being reachable. No local Linux privileges are required for the adjacent attacker in the paranoid interpretation, but the exact triggerability may depend on host Bluetooth policy, pairing state, controller behavior, and user or system activity. Namespaces and containers are not the main factor here because the important path is the host Bluetooth stack and controller-facing connection state. Call-site confidence: high, because the patch shows both the queueing call and the completion callback lifetime fix.

## 4. Severity interpretation

This is more serious than an ordinary cleanup bug because the commit explicitly identifies a theoretical UAF and fixes it with `hci_conn_get()` / `hci_conn_put()` lifetime management. Realistic exploitation evidence is limited: the patch does not show attacker-controlled reclaim, object replacement, type confusion, or arbitrary write. Conservatively it is a borderline Moderate UAF/DoS issue. Paranoid triage should treat it as Actionable Moderate at minimum because adjacent Bluetooth reachability plus async lifetime corruption has enough risk to require manual review.

## 5. One-sentence report phrase

A theoretical use-after-free in Bluetooth BIG Create Sync handling can occur because an asynchronous hci_sync callback used a raw hci_conn pointer without holding a reference, allowing an adjacent Bluetooth-triggered race to cause stale object access and possible kernel crash.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED.

Reason: this is an explicit race-based UAF in an adjacent Bluetooth path with async callback lifetime semantics. No strong LPE primitive is proven, but it should not be auto-closed because stale `hci_conn` access may be more than a simple DoS depending on object reuse and reachable Bluetooth workflows.

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

Patch: Bluetooth: hci_sync: hold conn in hci_connect_big_sync() callback [ Upstream
Commit: 2d91e6244b69d752503b2d44020d8b0e323dbd38
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=2d91e6244b69d752503b2d44020d8b0e323dbd38

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=2d91e6244b69d752503b2d44020d8b0e323dbd38

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

The original Linux kernel CVE announcement for CVE-2026-74530 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74530

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: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: 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).