[CVE-2026-74535][MODERATE 7.0] Bluetooth: ISO: avoid deadlocks in iso_sock_timeout [ Upstream

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

CVE: CVE-2026-74535
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: Bluetooth: ISO: avoid deadlocks in iso_sock_timeout [ Upstream
Commit: 16d89a63e08280abeef7218970a3bbd7ca62b021
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=16d89a63e08280abeef7218970a3bbd7ca62b021
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74535
Analysis date: Sat, 15 Aug 2026 17:04:36 -0400
ActionableScore: 5
ActionableScore lower bound: 4
Actionable bucket: Strong Important candidate / Actionable Moderate at minimum
Manual review required: YES

Summary:
A race in Bluetooth ISO timeout handling can let delayed work outlive the connection object and race with connection deletion, causing deadlock or use-after-free with likely DoS and weak privilege-escalation concern.

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ABOUT THIS REPORT
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The original Linux kernel CVE announcement for CVE-2026-74535 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74535

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-2026-74535	MODERATE	CHECK WITH IMPACT FROM ORIG NN MODERATE	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-667;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 timeout handling can occur because iso_sock_timeout runs from delayed work while iso_conn_del may concurrently delete the ISO channel and drop the last connection reference. The delayed work was stored in iso_conn, and later cleanup can reach conn hcon iso_data after the related hci_conn has already been freed, creating a use-after-free condition and possible kernel crash. The same lifetime and locking pattern can also deadlock when synchronous timer disabling is performed while lock_sock is held, because the timeout worker also takes lock_sock. For the CVSS the PR:L because reliable triggering normally requires a local process that can create or operate Bluetooth ISO sockets, while a remote Bluetooth peer alone is not clearly sufficient from the patch context. The issue is not reachable over an IP network, but Bluetooth radio proximity or peer behavior may affect timing once a local ISO socket workflow exists. Impact is at least denial of service and the UAF primitive makes possible privilege escalation plausible enough for manual review.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 5)	YES	REMOTE DEADLOCK DANGER INIT UAF NETWORK TIMER KPANIC 	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

* Local unprivileged trigger: +1
  A local process can plausibly create or operate Bluetooth ISO sockets when Bluetooth ISO support and device access are available.

* Memory corruption, weak or indirect corruption candidate: +1
  The commit explicitly describes a UAF involving `iso_sock_timeout()` racing with `iso_conn_del()`. However, the patch does not demonstrate attacker-controlled reclaim, type confusion, callback control, or arbitrary write.

* Real lifetime corruption: +1
  The bug is a real lifetime issue: delayed work was tied to `iso_conn`, while `iso_conn` and the associated `hci_conn` could be freed concurrently.

* Reliable kernel crash / strong DoS: +1
  The bug can cause UAF-related crash and also a deadlock due to synchronous delayed-work disabling while `lock_sock` may be taken by the worker.

* Weak LPE concern, paranoid only: +1
  The UAF includes a stale access to `conn->hcon->iso_data = NULL`, which is a write to an object that may already be freed. The written value is constrained and no reclaim primitive is shown, so this is not a strong LPE signal, but it is enough for manual review.

* Hard or unreliable race / special timing required: -1
  Triggering requires a race between timeout work and connection teardown.

* Rare or configuration-dependent exposure: -1
  Bluetooth ISO is not as broadly exposed as core TCP/IP paths and requires Bluetooth ISO capable setup.

Paranoid total: 5. Conservative total: 4.

## 3. Reachability analysis

The most realistic trigger is local. A local user or process that can create and drive Bluetooth ISO sockets may be able to cause timeout and teardown races. A nearby Bluetooth peer may influence connection teardown or timing, but the patch does not support treating this as a direct network or fully remote trigger.

Namespaces do not clearly make this broadly reachable. Bluetooth socket access is usually host/device dependent and may be restricted by distro policy, device availability, or service mediation. This is not an IP network reachable bug.

Call-site confidence: high. The relevant timeout worker, connection delete path, socket close path, and lifetime movement from `iso_conn` to `iso_pinfo` are visible in the patch.

## 4. Severity interpretation

This is above ordinary Moderate because the patch explicitly fixes both a deadlock and a UAF in kernel Bluetooth object lifetime. Realistic exploitation evidence supports DoS more strongly than privilege escalation. Theoretical LPE is plausible enough for manual review because the bug includes stale freed-object access, but the patch does not show controlled reclaim, controlled payload, type confusion, or callback hijack.

Overall this behaves like an Actionable Moderate issue, with weak Important-candidate concern only under paranoid triage.

## 5. One-sentence report phrase

A race in Bluetooth ISO timeout handling can let delayed work outlive the connection object and race with connection deletion, causing deadlock or use-after-free with likely DoS and weak privilege-escalation concern.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

Reason: explicit UAF plus race in kernel object lifetime. The known practical impact is DoS, but the stale freed-object write makes this unsuitable for automatic closure.

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

Patch: Bluetooth: ISO: avoid deadlocks in iso_sock_timeout [ Upstream
Commit: 16d89a63e08280abeef7218970a3bbd7ca62b021
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=16d89a63e08280abeef7218970a3bbd7ca62b021

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=16d89a63e08280abeef7218970a3bbd7ca62b021

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

The original Linux kernel CVE announcement for CVE-2026-74535 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74535

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).