[CVE-2026-64434][IMPORTANT] Bluetooth: L2CAP: Fix UAF in channel timeout by holding conn ref [ Upstream

[CVE-2026-64434][IMPORTANT] Bluetooth: L2CAP: Fix UAF in channel timeout by holding conn ref [ Upstream

[AL-KERNEL]

CVE: CVE-2026-64434
Priority: IMPORTANT
AL-KERNEL base severity: IMPORTANT
KPANIC flag: YES
Patch: Bluetooth: L2CAP: Fix UAF in channel timeout by holding conn ref [ Upstream
Commit: 91047a4396a8b1857a6f712a90cf33ec0012b189
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=91047a4396a8b1857a6f712a90cf33ec0012b189
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64434
Analysis date: Sat, 25 Jul 2026 09:22:00 -0400
ActionableScore: 7
ActionableScore lower bound: 5
Actionable bucket: Strong Important candidate / Actionable Moderate at minimum
Manual review required: YES

Summary:
A Bluetooth L2CAP asynchronous channel timeout can access a freed `l2cap_conn` during connection teardown, causing a slab use-after-free and kernel crash, with adjacent Bluetooth reachability and possible memory corruption risk requiring manual review.

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

The original Linux kernel CVE announcement for CVE-2026-64434 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64434

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: IMPORTANT
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
======================================================================

CVE-2026-64434	IMPORTANT	CHECK WITH IMPACT FROM ORIG NN MODERATE	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-664;Other CVSS 'AV:A/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:H';BEST CVSS score: '7.5';DESCR 'A use-after-free exists in the Bluetooth L2CAP channel timeout path because l2cap_chan_timeout() can run asynchronously after the underlying l2cap_conn object has been freed. The worker then accesses chan conn and may try to lock a freed conn lock, which can crash the kernel and may represent a memory corruption primitive rather than a pure NULL pointer dereference. A remote Bluetooth peer may be able to influence L2CAP channel lifetime and disconnect timing from adjacent radio range, although reliable triggering depends on a race window and local Bluetooth stack state. For the CVSS the PR:N is used because the higher risk interpretation is an adjacent Bluetooth attacker that does not need an account on the victim system. Impact is at least denial of service via kernel crash and in the paranoid case may include confidentiality and integrity impact due to use-after-free memory corruption. This requires manual review because the bug class is UAF and the affected path is reachable through Bluetooth L2CAP behavior.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 7)  SKIP CVE-2026-64434 UNKNOWN SKIP The Fixes patch not applied yet, so unlikely that actual: 8c8e620467a7b51562dbcefbd1f09f288d7d710d YES  NO NO unknown 	MAYBE	REMOTE OOB LOCK DANGER UAF NETWORK HARDWARE TEST KPANIC  KPANIC INCREASED_TO_HIGH_BASED_ON_GUESSCVSS	-	-	checked

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ACTIONABLESCORE ANALYSIS
======================================================================

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:

* Remote reachable / network-triggerable: **+2**. The affected path is Bluetooth L2CAP, reachable by an adjacent Bluetooth peer rather than ordinary IP networking.
* Memory corruption, weak race-UAF primitive: **+1**. The bug is a real UAF, but the conservative interpretation treats it as race-dependent stale pointer use without demonstrated attacker-controlled reclaim.
* Real lifetime corruption: **+1**. The patch fixes missing lifetime protection by adding an `l2cap_conn_get()` reference and releasing it in channel destruction.
* Reliable kernel crash / strong DoS: **+1**. KASAN shows slab-use-after-free in `mutex_lock()` from `l2cap_chan_timeout()`.
* Hard or unreliable race / special timing required: **-1**. Triggering depends on asynchronous timeout work racing connection teardown.
* Broad/default/common subsystem exposure: **+1**. Bluetooth L2CAP is a common kernel subsystem on systems with Bluetooth enabled.

Paranoid additional signals:

* Memory corruption, strong corruption primitive: upgrade from **+1 to +2**. KASAN reports a write of size 8 into freed `kmalloc-512` memory while locking the freed `conn->lock`.
* Weak LPE concern: **+1**. There is writable stale object access in freed heap memory, but no demonstrated reclaim, object replacement, callback control, or arbitrary write.

## 3. Reachability analysis

A malicious Bluetooth peer within radio range may be able to influence L2CAP channel lifetime, timeout scheduling, and disconnection timing. No local account on the victim is required for the higher-risk adjacent attacker model, so PR is effectively none for that model. Reliable exploitation still depends on a race between asynchronous L2CAP timeout workers and connection teardown.

The provided trace uses `vhci_release()` in the freeing path, which may represent a local or test harness reproduction, but the vulnerable objects and call paths are normal Bluetooth L2CAP connection state. Bluetooth must be enabled and reachable. This is not Internet-reachable IP networking, but it is externally reachable over adjacent radio exposure.

Namespaces do not materially reduce the concern for the adjacent Bluetooth model. Local namespace or container access is not the main trigger assumption here.

Call-site confidence: **high**. The patch includes the timeout worker, channel deletion, channel destruction, and changed lifetime/reference behavior.

## 4. Severity interpretation

This is not an ordinary Moderate cleanup bug. It is a confirmed UAF in an asynchronous Bluetooth L2CAP worker with a demonstrated freed-object access and kernel crash. Conservative handling is **Actionable Moderate** because exploitation requires timing and no concrete LPE primitive is shown.

The paranoid interpretation is a **Strong Important candidate** because the stale access includes a write into freed heap memory and the path may be reachable by an adjacent unauthenticated Bluetooth peer. Theoretical memory corruption risk is credible, but realistic privilege escalation is not demonstrated from the patch alone.

## 5. One-sentence report phrase

A Bluetooth L2CAP asynchronous channel timeout can access a freed `l2cap_conn` during connection teardown, causing a slab use-after-free and kernel crash, with adjacent Bluetooth reachability and possible memory corruption risk requiring manual review.

## 6. Manual review recommendation

**MANUAL CHECK REQUIRED**

Reason: confirmed UAF, externally adjacent Bluetooth reachability, asynchronous race timing, and a KASAN-reported write into freed heap memory make this unsuitable for auto-close even though practical LPE is not demonstrated.

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

Patch: Bluetooth: L2CAP: Fix UAF in channel timeout by holding conn ref [ Upstream
Commit: 91047a4396a8b1857a6f712a90cf33ec0012b189
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=91047a4396a8b1857a6f712a90cf33ec0012b189

Changed files:
  include/linux/instrumented.h
  include/linux/atomic/atomic-instrumented.h
  kernel/locking/mutex.c
  net/bluetooth/l2cap_core.c
  kernel/workqueue.c
  kernel/kthread.c
  arch/x86/kernel/process.c
  arch/x86/entry/entry_64.S
  include/net/bluetooth/hci_core.h
  net/bluetooth/hci_event.c
  net/bluetooth/hci_core.c
  net/bluetooth/hci_conn.c
  net/bluetooth/hci_sync.c
  drivers/bluetooth/hci_vhci.c
  fs/file_table.c
  kernel/task_work.c
  kernel/signal.c
  arch/x86/kernel/signal.c
  kernel/entry/common.c
  arch/x86/entry/syscall_64.c
  include/net/bluetooth/l2cap.h

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=91047a4396a8b1857a6f712a90cf33ec0012b189

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

The original Linux kernel CVE announcement for CVE-2026-64434 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64434

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:A/AC:H/PR:N/UI:N/S:U/C:L/I:L/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: 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: IMPORTANT
KPANIC detected for this report: YES
Published priority for this report (same as in Subject): IMPORTANT

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).