[CVE-2026-74529][MODERATE 7.0] Bluetooth: hci_sync: hold conn in hci_connect_pa_sync() callback [ Upstream

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

CVE: CVE-2026-74529
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: Bluetooth: hci_sync: hold conn in hci_connect_pa_sync() callback [ Upstream
Commit: c53c70ec289ee12f20c4f1b2fbfd151762c01f67
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=c53c70ec289ee12f20c4f1b2fbfd151762c01f67
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74529
Analysis date: Sat, 15 Aug 2026 13:09:41 -0400
ActionableScore: 5
ActionableScore lower bound: 4
Actionable bucket: Actionable Moderate at minimum**:: Not enough evidence for Strong Important, but should not be auto-closed.
Manual review required: YES

Summary:
Bluetooth hci_sync could use a freed hci_conn in the PA sync completion path if connection teardown races with queued async work, allowing at least an adjacent-triggered kernel crash and requiring manual review because the primitive is a real lifetime UAF.

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ABOUT THIS REPORT
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The original Linux kernel CVE announcement for CVE-2026-74529 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74529

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-2026-74529	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-664;Other CVSS 'AV:A/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '7.5';DESCR 'Bluetooth hci_sync has a theoretical use after free because hci_connect_pa_sync queues work with a raw hci_conn pointer and the connection can be released before create_pa_complete runs. A nearby Bluetooth peer may help trigger the lifetime race by affecting PA sync setup or connection teardown while the queued hci_sync callback is pending, so the vector is adjacent wireless access rather than Internet reachable access. For the CVSS the PR:N is used for the paranoid score because the attacker does not need local privileges on the victim if the vulnerable Bluetooth role and reachable peer interaction are present. Impact is at least denial of service via kernel crash. Because the primitive is UAF, the worst case is kept at C:H/I:H/A:H for manual review sensitivity, although reliable privilege escalation is not proven by the diff.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate at minimum (with actual score 5)	YES	REMOTE UAF NETWORK  DECREASED_TO_MODERATE70_BASED_ON_ACTIONABLESCORELOWERTHAN6 DECREASED_TO_MODERATEREG_BASED_ON_FALSEPOSCHECKOFKP	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**:: Not enough evidence for Strong Important, but should not be auto-closed.

## 2. Signal breakdown

Paranoid score signals:

* Remote reachable / network-triggerable adjacent path: +2
  Bluetooth peer interaction can plausibly influence PA sync setup or teardown, but this is adjacent wireless exposure, not Internet reachable AV:N.
* Memory corruption, weak primitive: +1
  The patch explicitly prevents a theoretical UAF, but there is no shown attacker-controlled reclaim, overwrite, type confusion, or function pointer control.
* Real lifetime corruption: +1
  The bug is a refcount/lifetime mismatch where hci_sync work may outlive the hci_conn object.
* Reliable kernel crash / strong DoS: +1
  A stale hci_conn dereference in an async callback can plausibly crash the kernel.

Conservative adjustment:

* Hard or unreliable race / special timing required: -1
  The UAF depends on conn free racing with queued hci_sync completion.

Race-UAF downgrade applied: this is treated as weak UAF memory corruption, not strong LPE-grade corruption.

## 3. Reachability analysis

A nearby Bluetooth peer may help trigger the vulnerable state if the system is acting in the affected Bluetooth role and PA sync creation or cancellation overlaps with connection teardown. No local account is required in the paranoid interpretation, but physical radio proximity and Bluetooth configuration are required. This is not a normal routable network attack. Namespaces do not materially improve reachability for a remote Bluetooth peer, but local management of Bluetooth roles may require privileges.

Call-site confidence: high, because the patch shows both the async queueing site and the completion callback lifetime fix.

## 4. Severity interpretation

This behaves like an actionable Moderate issue. Theoretical memory corruption is present because the commit explicitly says UAF and the fix adds hci_conn_get/hci_conn_put around async work. Realistic exploitation evidence is limited because the patch does not show reclaim control, write-after-free, object replacement, or privilege escalation. The main demonstrated impact is DoS, while paranoid triage keeps it above auto-close due to adjacent-triggerable kernel UAF.

## 5. One-sentence report phrase

Bluetooth hci_sync could use a freed hci_conn in the PA sync completion path if connection teardown races with queued async work, allowing at least an adjacent-triggered kernel crash and requiring manual review because the primitive is a real lifetime UAF.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

Reason: adjacent-reachable Bluetooth UAF with async lifetime semantics should be reviewed manually even though the available patch evidence supports DoS more strongly than privilege escalation.

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

Patch: Bluetooth: hci_sync: hold conn in hci_connect_pa_sync() callback [ Upstream
Commit: c53c70ec289ee12f20c4f1b2fbfd151762c01f67
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=c53c70ec289ee12f20c4f1b2fbfd151762c01f67

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=c53c70ec289ee12f20c4f1b2fbfd151762c01f67

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

The original Linux kernel CVE announcement for CVE-2026-74529 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74529

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:N/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: 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: 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).