[CVE-2026-74537][MODERATE 7.0] Bluetooth: ISO: hold sk properly in iso_conn_ready [ Upstream

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

CVE: CVE-2026-74537
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: Bluetooth: ISO: hold sk properly in iso_conn_ready [ Upstream
Commit: 4e9b5e8669b3602a4e01b6d1e9539b72e42c84d5
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=4e9b5e8669b3602a4e01b6d1e9539b72e42c84d5
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74537
Analysis date: Sat, 15 Aug 2026 12:53:58 -0400
ActionableScore: 5
ActionableScore lower bound: 4
Actionable bucket: Strong Important candidate / Actionable Moderate at minimum**:: Actionable Moderate at minimum. Not auto-close.
Manual review required: YES

Summary:
A race in Bluetooth ISO connection setup can leave `iso_conn_ready()` using a socket after concurrent close and free, causing a kernel UAF that is realistically a local DoS and requires manual review for possible escalation risk.

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ABOUT THIS REPORT
======================================================================

The original Linux kernel CVE announcement for CVE-2026-74537 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74537

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-2026-74537	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-667;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:H';BEST CVSS score: '7';DESCR 'A race in Bluetooth ISO connection setup can allow iso_conn_ready to dereference a sock after a concurrent iso_sock_release clears and kills the socket. The vulnerable path reads conn sk without holding conn lock or a socket reference, then lock_sock can operate on a freed sock and trigger a use-after-free. A local process that can create and close Bluetooth ISO sockets can race against connection ready processing, and a nearby Bluetooth peer may help generate the timing events. For the CVSS the PR:L is used because reliable triggering still requires a local user or process context on the target. Impact is at least local denial of service via kernel crash and in the paranoid case may include confidentiality and integrity impact because this is a real kernel use-after-free on struct sock rather than a pure NULL dereference.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 5)	YES	REMOTE OOB LOCK DANGER UAF NETWORK KPANIC  KPANIC DECREASED_TO_MODERATE70_BASED_ON_ACTIONABLESCORELOWERTHAN6	NO	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**:: Actionable Moderate at minimum. Not auto-close.

## 2. Signal breakdown

Conservative signals:

* Local unprivileged trigger: **+1**. A local process that can create and close Bluetooth ISO sockets can participate in the race.
* Firmware-mediated external influence: **+1**. A nearby Bluetooth peer/controller event can help drive the connection-ready path, but this is not ordinary network remote reachability.
* Memory corruption, weak primitive: **+1**. The patch explicitly describes UAF on `sk` dereference, but does not show attacker-controlled reclaim, type confusion, callback control, or write-after-free.
* Real lifetime corruption: **+1**. The fix adds socket refcounting via `iso_sock_hold()` and `sock_put()`, confirming a lifetime/refcount bug.
* Reliable kernel crash / strong DoS: **+1**. `lock_sock(sk)` or later socket operations on a freed `struct sock` can plausibly crash the kernel.
* Hard or unreliable race: **-1**. Triggering requires a timing window between `iso_conn_ready()` and concurrent socket release.

Paranoid additional signal:

* Availability impact realistic: **+1**. In the paranoid score, the UAF is treated as a host-wide crash risk that should not be auto-closed without manual review.

Not awarded:

* Strong LPE plausibility: **+0**. No demonstrated reclaim, attacker-controlled object replacement, function pointer control, refcount takeover, or arbitrary write.
* Confidentiality / Integrity: **+0 conservative**. The patch supports UAF/DoS, but not a concrete leak or write primitive.
* Remote reachable: **+0**. Bluetooth proximity or controller-mediated behavior is not the same as IP network remote reachability.

Call-site confidence: **high**. The relevant caller path and fix are visible in the supplied diff.

## 3. Reachability analysis

The likely trigger requires local code execution able to open and close Bluetooth ISO sockets while connection-ready processing occurs. A nearby Bluetooth peer may help generate timing events, but the attacker still needs local process context for reliable triggering. Namespaces may matter if Bluetooth socket access is delegated into containers, but typical exploitation is local and configuration-dependent. The path requires Bluetooth ISO support and relevant Bluetooth hardware/controller behavior, so exposure is narrower than core networking but not rare enough to dismiss.

## 4. Severity interpretation

This behaves like an **Actionable Moderate** issue with memory-lifetime risk. The realistic impact is kernel crash/DoS from a race-dependent UAF. Theoretical LPE is worth manual review because the object is a kernel `struct sock`, but the patch does not show a strong exploitation primitive. Under the race-UAF downgrade rule, this should not be treated as a strong Important solely from the UAF label.

## 5. One-sentence report phrase

A race in Bluetooth ISO connection setup can leave `iso_conn_ready()` using a socket after concurrent close and free, causing a kernel UAF that is realistically a local DoS and requires manual review for possible escalation risk.

## 6. Manual review recommendation

**MANUAL CHECK REQUIRED**.
YES REQUIRES MANUAL CHECK because this is an explicit kernel UAF on `struct sock`, even though the demonstrated primitive is race-dependent and mainly supports DoS.

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

Patch: Bluetooth: ISO: hold sk properly in iso_conn_ready [ Upstream
Commit: 4e9b5e8669b3602a4e01b6d1e9539b72e42c84d5
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=4e9b5e8669b3602a4e01b6d1e9539b72e42c84d5

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=4e9b5e8669b3602a4e01b6d1e9539b72e42c84d5

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

The original Linux kernel CVE announcement for CVE-2026-74537 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74537

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: 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).