[CVE-2026-64557][MODERATE 7.0] Bluetooth: L2CAP: Fix use-after-free in l2cap_sock_new_connection_cb() [ Upstream

[CVE-2026-64557][MODERATE 7.0] Bluetooth: L2CAP: Fix use-after-free in l2cap_sock_new_connection_cb() [ Upstream

[AL-KERNEL]

CVE: CVE-2026-64557
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: Bluetooth: L2CAP: Fix use-after-free in l2cap_sock_new_connection_cb() [ Upstream
Commit: b39298044e5534612511a2ff5de03ba5f6e7a820
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=b39298044e5534612511a2ff5de03ba5f6e7a820
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64557
Analysis date: Wed, 29 Jul 2026 04:51:44 -0400
ActionableScore: 5
ActionableScore lower bound: 4
Actionable bucket: Actionable Moderate at minimum
Manual review required: YES

Summary:
Bluetooth L2CAP contains a race in the incoming connection path where a child socket can be exposed and freed after `release_sock(parent)` while the callback still dereferences its channel state, causing a use-after-free reachable by an adjacent Bluetooth peer and requiring manual review.

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

The original Linux kernel CVE announcement for CVE-2026-64557 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64557

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-2026-64557	MODERATE	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-667;Other CVSS 'AV:A/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:H';BEST CVSS score: '7.5';DESCR 'Bluetooth L2CAP has a race in the incoming connection path where l2cap_sock_new_connection_cb() can expose a newly created child socket through the accept queue before the child channel lifetime is safely owned by the core. After release_sock(parent), another task may accept and free the child socket while the callback still dereferences the related channel pointer, causing a use-after-free. For the CVSS the PR:N is used because a peer in Bluetooth range does not need local credentials on the victim when a reachable L2CAP service accepts incoming connections. The attack vector is adjacent network rather than Internet remote because Bluetooth requires radio proximity. Attack complexity is high because reliable triggering depends on a race window between connection handling and accept or close activity. Impact is at least denial of service via kernel crash and in the paranoid interpretation may include confidentiality and integrity impact due to kernel use-after-free memory corruption. YES REQUIRES MANUAL CHECK';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate at minimum (with actual score 5)	YES	REMOTE DANGER INIT UAF NETWORK KPANIC  KPANIC INCREASED_TO_HIGH_BASED_ON_GUESSCVSS KPANIC DECREASED_TO_MODERATE70_BASED_ON_ACTIONABLESCORELOWERTHAN7	NO	NO	guess

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

ActionableScore=5
ActionableScoreLower=4

## 1. ActionableScore

* Conservative score: **4**
* Paranoid score: **5**
* Final recommended bucket: **Actionable Moderate at minimum**::

## 2. Signal breakdown

Conservative signals:

* **Remote reachable / network-triggerable: +2**
  Bluetooth L2CAP is reachable by a peer over Bluetooth radio proximity. This is adjacent-network exposure, not Internet remote, but it is still externally triggerable without local code execution on the victim.

* **Memory corruption, weak primitive: +1**
  The patch and commit explicitly describe a use-after-free after `release_sock(parent)`, but do not show controlled reclaim, object replacement, write-after-free, type confusion, callback control, or refcount takeover.

* **Real lifetime corruption: +1**
  The bug is a real lifetime issue: a child socket can become reachable through the accept queue and be freed while the callback still dereferences state derived from it.

* **Reliable kernel crash / strong DoS: +1**
  A UAF in the Bluetooth socket/channel path can realistically crash the kernel.

* **Hard or unreliable race / special timing required: -1**
  Exploitation depends on a race between exposing the child socket through the accept queue and another task accepting/freeing it before the callback dereferences it.

Conservative total: **4**

Paranoid additional signal:

* **Broad/common subsystem exposure: +1**
  Bluetooth L2CAP is a standard Linux kernel networking subsystem on systems with Bluetooth enabled. This raises triage priority even though exposure is adjacent-network and configuration-dependent.

Paranoid total: **5**

Race-UAF downgrade applied: this is a race-dependent UAF where the patch prevents a stale pointer from surviving concurrent accept/free activity. No demonstrated reclaim, write primitive, type confusion, callback dispatch, or refcount takeover is shown, so the conservative score is capped at **4** and the paranoid score at **5**.

Call-site confidence: **high**. The patch includes the relevant callback API change and the main L2CAP connection call sites.

## 3. Reachability analysis

A nearby Bluetooth peer can plausibly trigger the affected L2CAP incoming connection path when the victim has Bluetooth enabled and a reachable L2CAP service/listener. No local user account on the victim is required for the remote peer, so this is not a local-only interface. The vector is adjacent-network rather than general Internet remote because Bluetooth requires radio proximity and pairing/service exposure may affect practical reachability.

Namespaces and containers do not materially reduce the external Bluetooth peer requirement. Local process behavior on the victim, such as accept/close timing on the socket, may influence race reliability. This makes exploitation timing-sensitive, but not purely theoretical.

## 4. Severity interpretation

This behaves above ordinary Moderate because it is an externally reachable kernel UAF in a networking-adjacent subsystem. It should not be auto-closed as a simple DoS-only bug.

Realistic evidence supports **kernel crash / DoS** and a real lifetime bug. Theoretical memory corruption potential exists because the object can be freed before dereference, but the patch does not demonstrate attacker-controlled reclaim, object replacement, write-after-free, type confusion, or a direct LPE primitive. Therefore the main result is **Actionable Moderate**, with manual review required before treating it as a full Important-class LPE.

## 5. One-sentence report phrase

Bluetooth L2CAP contains a race in the incoming connection path where a child socket can be exposed and freed after `release_sock(parent)` while the callback still dereferences its channel state, causing a use-after-free reachable by an adjacent Bluetooth peer and requiring manual review.

## 6. Manual review recommendation

**MANUAL CHECK REQUIRED**

Reason: this is a real kernel UAF in an externally reachable Bluetooth/L2CAP path. The current patch context supports Actionable Moderate handling, and further manual analysis is needed to determine whether reliable reclaim or privilege escalation is practical.

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

Patch: Bluetooth: L2CAP: Fix use-after-free in l2cap_sock_new_connection_cb() [ Upstream
Commit: b39298044e5534612511a2ff5de03ba5f6e7a820
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=b39298044e5534612511a2ff5de03ba5f6e7a820

Changed files:
  include/net/bluetooth/l2cap.h
  net/bluetooth/6lowpan.c
  net/bluetooth/l2cap_core.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=b39298044e5534612511a2ff5de03ba5f6e7a820

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

The original Linux kernel CVE announcement for CVE-2026-64557 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64557

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: 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).