[CVE-2026-74533][MODERATE 7.0] Bluetooth: ISO: fix race of kfree vs kref_get_unless_zero [ Upstream

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

CVE: CVE-2026-74533
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: Bluetooth: ISO: fix race of kfree vs kref_get_unless_zero [ Upstream
Commit: 876a3e94c70d0859d1dad1c986112d4f0d99eba8
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=876a3e94c70d0859d1dad1c986112d4f0d99eba8
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74533
Analysis date: Sat, 15 Aug 2026 12:14:33 -0400
ActionableScore: 5
ActionableScore lower bound: 4
Actionable bucket: Actionable Moderate at minimum
Manual review required: YES

Summary:
A race in Bluetooth ISO connection lifetime handling can allow `hci_conn::iso_data` to be used after the related `iso_conn` object is freed, leading to a kernel crash and requiring manual review for potential UAF exploitability.

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ABOUT THIS REPORT
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The original Linux kernel CVE announcement for CVE-2026-74533 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74533

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-2026-74533	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-667;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '7.5';DESCR 'A race in Bluetooth ISO connection lifetime handling can cause a use-after-free because hci_conn::iso_data was read and cleared without a common lock while kref_get_unless_zero() could run concurrently with kfree(). The vulnerable path involves iso_recv using hcon::iso_data while another task releases the same iso_conn, so a stale pointer may be dereferenced in kernel context. For the CVSS the PR:N value is used for the paranoid score because a Bluetooth adjacent peer may be able to influence ISO receive and disconnect timing without local privileges on the target, although reliable triggering likely requires an active ISO capable Bluetooth setup and a narrow race window. The issue is not Internet reachable but can be adjacent-network reachable over Bluetooth radio range. Impact is at least denial of service via kernel crash and in worst case may allow confidentiality or integrity impact due to kernel use-after-free, so manual review is required.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate at minimum (with actual score 5)	YES	REMOTE LOCK INIT RACE UAF NETWORK DEBUGFS KPANIC  KPANIC DECREASED_TO_MODERATE70_BASED_ON_ACTIONABLESCORELOWERTHAN6	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**

## 2. Signal breakdown

Conservative signals:

* Local unprivileged trigger: +1. A local user may be able to exercise Bluetooth ISO socket and connection lifetime paths, depending on local Bluetooth policy and hardware availability.
* Memory corruption, weak race-UAF primitive: +1. The patch explicitly describes `kref_get_unless_zero()` racing with `kfree(conn)`, but does not show attacker-controlled reclaim, type confusion, callback control, or write-after-free.
* Real lifetime corruption: +1. This is a real object lifetime bug involving `hci_conn::iso_data`, kref lifetime, and freeing of `iso_conn`.
* Reliable kernel crash / strong DoS: +1. A stale pointer dereference in kernel context can plausibly crash the kernel.
* Hard or unreliable race: -1. The trigger depends on a timing window between receive processing and connection release.
* Broad kernel subsystem exposure: +1. Bluetooth is a common kernel subsystem, although ISO-specific exposure depends on LE Audio or ISO-capable setup.

Paranoid additional interpretation:

* Adjacent / Bluetooth-radio trigger treated as network-like external reachability: +1 effective uplift. A nearby Bluetooth peer may influence ISO receive and disconnect timing, but this is not Internet-reachable and requires Bluetooth ISO conditions.
* Paranoid score is capped at 5 by the race-UAF downgrade rule because the patch shows UAF but not controlled reclaim, object replacement, callback dispatch, arbitrary write, or demonstrated LPE.

## 3. Reachability analysis

The bug is reachable through Bluetooth ISO connection handling. The local path is more defensible for conservative scoring because a local process can participate in ISO socket lifecycle and disconnect behavior if Bluetooth access is allowed. A paranoid interpretation also considers an adjacent Bluetooth peer in radio range, because `iso_recv()` is driven by received ISO traffic and could race with local or stack-driven connection teardown.

Namespaces and containers may matter if Bluetooth device access or AF_BLUETOOTH sockets are delegated into a container. In typical hardened deployments, Bluetooth access may be restricted or absent, but on desktops, laptops, and systems using LE Audio, the subsystem is realistic. The affected path is not Internet reachable and requires Bluetooth hardware plus ISO-capable use cases.

## 4. Severity interpretation

This is not an ordinary cleanup bug. It is a real race-dependent UAF in a kernel protocol object lifetime path. Realistic impact is most strongly supported as local or adjacent denial of service via kernel crash.

Privilege escalation is not strongly demonstrated because the patch does not show controlled reclaim, stale object replacement, write-after-free, type confusion, or callback control. However, kernel UAF in a protocol stack is historically worth manual review, so it should be treated as Actionable Moderate at minimum rather than auto-closed.

## 5. One-sentence report phrase

A race in Bluetooth ISO connection lifetime handling can allow `hci_conn::iso_data` to be used after the related `iso_conn` object is freed, leading to a kernel crash and requiring manual review for potential UAF exploitability.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

Reason: the patch explicitly fixes a UAF race between `kfree()` and `kref_get_unless_zero()` in Bluetooth ISO lifetime handling. No concrete LPE primitive is shown, but the memory lifetime class and possible adjacent Bluetooth influence make it unsuitable for automatic closure.

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

Patch: Bluetooth: ISO: fix race of kfree vs kref_get_unless_zero [ Upstream
Commit: 876a3e94c70d0859d1dad1c986112d4f0d99eba8
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=876a3e94c70d0859d1dad1c986112d4f0d99eba8

Changed files:
  include/net/bluetooth/hci_core.h
  net/bluetooth/hci_conn.c
  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=876a3e94c70d0859d1dad1c986112d4f0d99eba8

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

The original Linux kernel CVE announcement for CVE-2026-74533 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74533

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: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: 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).