[CVE-2026-74534][MODERATE 7.0] Bluetooth: ISO: fix refcounting of iso_conn [ Upstream

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

CVE: CVE-2026-74534
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: Bluetooth: ISO: fix refcounting of iso_conn [ Upstream
Commit: 3b921533e8aa95b77aadcf31737595578e735f3c
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=3b921533e8aa95b77aadcf31737595578e735f3c
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74534
Analysis date: Sat, 15 Aug 2026 16:16:55 -0400
ActionableScore: 5
ActionableScore lower bound: 4
Actionable bucket: Strong Important candidate / Actionable Moderate at minimum
Manual review required: YES

Summary:
A race between `iso_conn_del()` and `iso_chan_del()` in Bluetooth ISO can double-put an `iso_conn` reference, creating a kernel use-after-free that is locally triggerable through Bluetooth ISO socket activity and may cause a crash or require review for possible privilege escalation.

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ABOUT THIS REPORT
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The original Linux kernel CVE announcement for CVE-2026-74534 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74534

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-2026-74534	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-911;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '7';DESCR 'A race in Bluetooth/ISO connection teardown can cause a double put of iso_conn when iso_conn_del runs concurrently with iso_chan_del. The resulting refcount imbalance can free the connection object while another path still operates on it, creating a use-after-free condition in kernel memory. For the CVSS the PR:L is used because reliable triggering appears to require a local user process or local service that can create or tear down Bluetooth ISO sockets. The issue is not directly reachable over normal IP networking. A nearby Bluetooth peer may help influence connection events, but the patch context still points to a local endpoint race rather than a purely remote trigger. Impact is at least local denial of service via kernel crash. In the paranoid score, impact is raised to C:H/I:H/A:H because the bug class is explicit UAF from refcounting and may allow privilege escalation if heap reuse can be controlled.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 5)	YES	REMOTE RACE UAF NETWORK 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: **Strong Important candidate / Actionable Moderate at minimum**::

## 2. Signal breakdown

**Conservative signals:**

* **Local unprivileged trigger: +1**
  A local process that can use Bluetooth ISO sockets can plausibly participate in connection setup and teardown paths.

* **Generic memory corruption, strong corruption primitive: +2**
  The commit explicitly describes a double-put of `iso_conn` and marks the second put as `UAF`. This is a real refcount lifetime bug, not just a warning or bookkeeping mismatch.

* **Real lifetime corruption: +1**
  The patch changes ownership of the `iso_conn` reference so that `iso_pi(sk)->conn` owns a refcount while non-NULL. This directly fixes object lifetime corruption.

* **Hard or unreliable race / special timing required: -1**
  The issue requires a race between `iso_conn_del()` and `iso_chan_del()`.

* **Reliable kernel crash / strong DoS: +1**
  A double-put leading to UAF can realistically cause kernel crash or memory corruption symptoms.

**Conservative total: 4**

**Paranoid additional signal:**

* **Weak LPE concern: +1**
  Because this is an explicit kernel UAF caused by refcount imbalance in a socket-related subsystem, privilege escalation is not proven but should not be dismissed without manual review.

**Paranoid total: 5**

## 3. Reachability analysis

The likely trigger is local and requires a process or service that can create and tear down Bluetooth ISO sockets while Bluetooth connection events are also processed. A nearby Bluetooth peer may influence connection timing, but the patch context does not support treating this as a purely remote network-triggerable bug. This is not reachable through normal IP networking.

Namespaces may matter if Bluetooth socket access is delegated into containers or service sandboxes. In typical deployments this is still a local attack surface, not a full root-only path. Bluetooth is common as a subsystem, but ISO usage is less common than classic Bluetooth or BLE, so exposure is configuration and hardware dependent.

Call-site confidence: **high**, because the patch includes the relevant refcounting call paths in `iso_conn_add()`, `iso_chan_add()`, `iso_conn_del()`, and connection confirmation paths.

## 4. Severity interpretation

This is stronger than an ordinary Moderate because the patch fixes an explicit UAF-producing refcount race. Realistic exploitation evidence points first to local DoS or unstable memory corruption. Theoretical privilege escalation is plausible enough for manual review, but the patch does not show attacker-controlled reclaim, object replacement, callback control, or an arbitrary write primitive.

Therefore this should be treated as **Actionable Moderate at minimum**, with **Important-candidate review** if the affected product exposes Bluetooth ISO sockets to unprivileged local users or containerized workloads.

## 5. One-sentence report phrase

A race between `iso_conn_del()` and `iso_chan_del()` in Bluetooth ISO can double-put an `iso_conn` reference, creating a kernel use-after-free that is locally triggerable through Bluetooth ISO socket activity and may cause a crash or require review for possible privilege escalation.

## 6. Manual review recommendation

**MANUAL CHECK REQUIRED**

YES REQUIRES MANUAL CHECK. The bug is an explicit refcount UAF in kernel networking code, and although exploitation beyond DoS is not demonstrated, this class historically requires manual review for reclaimability and local privilege escalation potential.

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

Patch: Bluetooth: ISO: fix refcounting of iso_conn [ Upstream
Commit: 3b921533e8aa95b77aadcf31737595578e735f3c
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=3b921533e8aa95b77aadcf31737595578e735f3c

Changed files:
  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=3b921533e8aa95b77aadcf31737595578e735f3c

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

The original Linux kernel CVE announcement for CVE-2026-74534 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74534

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: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: 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).