[CVE-2026-74528][MODERATE 7.0] Bluetooth: hci_sync: hold conn in hci_past_sync() callback [ Upstream

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

CVE: CVE-2026-74528
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: Bluetooth: hci_sync: hold conn in hci_past_sync() callback [ Upstream
Commit: e6792adef614b389141b142e30ee549e4a47dd7d
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=e6792adef614b389141b142e30ee549e4a47dd7d
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74528
Analysis date: Sat, 15 Aug 2026 10:07:37 -0400
ActionableScore: 7
ActionableScore lower bound: 5
Actionable bucket: Strong Important candidate / Actionable Moderate at minimum
Manual review required: YES

Summary:
A use-after-free race in the Bluetooth hci_sync PAST callback can pass freed hci_conn pointers to hci_conn_valid after kmalloc reuse, allowing a local Bluetooth-capable process to crash the kernel and potentially requiring manual review for higher impact memory corruption.

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ABOUT THIS REPORT
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The original Linux kernel CVE announcement for CVE-2026-74528 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74528

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-2026-74528	MODERATE	CHECK WITH IMPACT FROM ORIG NN IMPORTANT	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H';*CWE-416;CWE-362;*CWE-672;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:H';BEST CVSS score: '7';DESCR 'A use-after-free race exists in the Bluetooth hci_sync PAST path because hci_past_sync() queued an async command with raw hci_conn pointers without holding references. If the connection objects are freed before the completion callback runs, hci_conn_valid() or related callback logic can receive stale pointers that may already have been reused by kmalloc. For the CVSS the PR:L is used because a local user or local process with access to Bluetooth ISO or PAST related operations may be able to trigger the path without full administrative privileges in some deployments. The issue is not reachable over the Internet and is mainly a local Bluetooth control path problem, although a nearby Bluetooth peer or adapter state may be needed for practical triggering. Impact is at least local denial of service via kernel crash and in the paranoid case may allow confidentiality or integrity impact due to kernel use-after-free memory corruption, so it should be reviewed manually.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 7)  SKIP CVE-2026-74528 UNKNOWN SKIP The Fixes patch not applied yet, so unlikely that actual: d3413703d5f8 YES  NO NO unknown 	MAYBE	REMOTE UAF NETWORK KPANIC  DECREASED_TO_MODERATE7_BASED_ON_FALSEPOSCHECKOFKP	-	-	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=7
ActionableScoreLower=5

## 1. ActionableScore

* Conservative score: 5
* Paranoid score: 7
* Final recommended bucket: **Strong Important candidate / Actionable Moderate at minimum**::

## 2. Signal breakdown

Conservative signals:

* Local unprivileged trigger: +1. A local process that can reach Bluetooth ISO or PAST related operations may trigger the async hci_past_sync path without full host root in some deployments.
* Memory corruption, strong corruption primitive: +2. The patch fixes a real use-after-free class bug by adding hci_conn_get and hci_conn_put around async callback lifetime.
* Real lifetime corruption: +1. The bug is specifically a missing reference hold across hci_cmd_sync_queue_once and past_complete.
* Reliable kernel crash / strong DoS: +1. Passing freed hci_conn pointers to hci_conn_valid can plausibly crash the kernel.
* Weak LPE concern: +1. The commit explicitly says kmalloc may have reused the freed pointer, which makes this more than a pure stale NULL dereference, but no controlled reclaim or write primitive is shown.
* Hard or unreliable race / special timing required: -1. Exploitation depends on connection lifetime racing with asynchronous completion.

Conservative total: 5.

Paranoid additional signals:

* Confidentiality impact plausible: +1. Because the stale pointer may reference kmalloc reused memory, limited disclosure or object confusion cannot be ruled out without manual review.
* Integrity impact plausible: +1. Kernel UAF with reused memory may theoretically become an integrity primitive, although no arbitrary write or controlled callback target is demonstrated.

Paranoid total: 7.

## 3. Reachability analysis

This is not Internet remote reachable. The affected code is in the Bluetooth hci_sync PAST path and requires local interaction with Bluetooth connection state plus a practical race between hci_past_sync queuing and connection release. A nearby Bluetooth peer or controller state may be relevant for practical triggering, but the core trigger is a local Bluetooth control path rather than packet parsing from the public network.

Privileges are deployment dependent. If Bluetooth ISO or related socket operations are available to an unprivileged local user, PR:L is appropriate. If the product restricts these operations to CAP_NET_ADMIN or a privileged Bluetooth service, practical reachability is lower, but it is still not equivalent to full host root in all reduced-capability or service-account models. Namespaces usually do not make this a clean container escape by themselves, but delegated device or Bluetooth access can reduce practical privilege requirements.

Call-site confidence: high. The patch directly shows raw hci_conn pointers stored in async data, hci_cmd_sync_queue_once queuing the callback, and the fix adding reference holds and releases in completion and error paths.

## 4. Severity interpretation

This behaves above ordinary Moderate because it is a real kernel lifetime bug, not a validation-only fix or resource leak. The realistic demonstrated impact is local DoS through UAF-triggered crash. The theoretical risk is higher because the freed hci_conn pointer may be reused by kmalloc before callback validation, creating a plausible object lifetime corruption scenario.

There is not enough evidence to claim reliable privilege escalation, arbitrary code execution, or attacker-controlled reclaim. However, UAF plus explicit possible kmalloc reuse is sufficient for Actionable Moderate handling and manual review. The paranoid score reaches Strong Important candidate territory because confidentiality and integrity impact remain technically defensible for this bug class, but the conservative operational interpretation is Actionable Moderate.

## 5. One-sentence report phrase

A use-after-free race in the Bluetooth hci_sync PAST callback can pass freed hci_conn pointers to hci_conn_valid after kmalloc reuse, allowing a local Bluetooth-capable process to crash the kernel and potentially requiring manual review for higher impact memory corruption.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED.

Reason: this is a real kernel UAF lifetime issue in an async callback path, and the commit explicitly mentions freed pointer reuse by kmalloc. It should not be auto-closed as a simple DoS without reviewing whether local Bluetooth access, object reclaim, or reduced-privilege service models make exploitation more practical.

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UPSTREAM PATCH SUMMARY
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Patch: Bluetooth: hci_sync: hold conn in hci_past_sync() callback [ Upstream
Commit: e6792adef614b389141b142e30ee549e4a47dd7d
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=e6792adef614b389141b142e30ee549e4a47dd7d

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=e6792adef614b389141b142e30ee549e4a47dd7d

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

The original Linux kernel CVE announcement for CVE-2026-74528 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74528

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:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H
  The Best / paranoid CVSS score: 7

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: 5
  Paranoid ActionableScore: 7

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).