[CVE-2026-64406][MODERATE REGULAR] Bluetooth: fix UAF in bt_accept_dequeue()

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

CVE: CVE-2026-64406
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: Bluetooth: fix UAF in bt_accept_dequeue()
Commit: c0577c55219be42b6ea2ea8db11e85bfab6f4e8d
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=c0577c55219be42b6ea2ea8db11e85bfab6f4e8d
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64406
Analysis date: Sat, 25 Jul 2026 10:45:28 -0400
ActionableScore: 4
ActionableScore lower bound: 3
Actionable bucket: Borderline manual review recommended / Actionable Moderate candidate
Manual review required: YES

Summary:
A race dependent reference lifetime bug in Bluetooth L2CAP accept queue handling can cause `bt_accept_dequeue()` to access a freed socket during listening socket cleanup, leading to a local kernel crash with UAF based manual review relevance.

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

The original Linux kernel CVE announcement for CVE-2026-64406 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64406

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 REGULAR
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-2026-64406	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-672;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '7';DESCR 'A use after free can occur in the Bluetooth L2CAP accept queue path because bt_accept_dequeue() dropped the temporary reference from bt_accept_get() before unlinking the socket from the accept queue. If bt_accept_unlink() drops the final queue reference, later code can operate on freed sock memory during listening socket cleanup. For the CVSS the PR:L is used because reliable triggering requires a local user or process able to exercise Bluetooth L2CAP socket lifecycle operations, rather than a fully remote network packet alone. AC:H is used because the issue depends on a race or narrow lifetime window between accept queue walking, unlink, and concurrent teardown. The base impact is local denial of service via kernel crash, while the paranoid impact treats the confirmed use after free as memory corruption that may allow confidentiality and integrity impact in a worst still defensible interpretation. The issue is not directly reachable over normal IP networking, although Bluetooth adjacent interaction may contribute to the required L2CAP state in some deployments.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline manual review recommended / Actionable Moderate candidate (with actual score 4)  SKIP CVE-2026-64406 UNKNOWN SKIP The Fixes patch not applied yet, so unlikely that actual: ab1513597c6cf17cd1ad2a21e3b045421b48e022 YES  NO NO unknown 	MAYBE	REMOTE DANGER UAF NETWORK SYZBOT  DECREASED_TO_MODERATE70_BASED_ON_ACTIONABLESCORELOWERTHAN7 DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5	-	-	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=4
ActionableScoreLower=3

## 1. ActionableScore

* Conservative score: **3**
* Paranoid score: **4**
* Final recommended bucket: **Borderline manual review recommended / Actionable Moderate candidate**::

## 2. Signal breakdown

Triggered signals:

* **Local unprivileged trigger: +1**
  Likely reachable by a local user or process able to exercise Bluetooth L2CAP socket lifecycle operations.

* **Memory corruption, weak primitive: +1**
  This is a confirmed UAF, but it is race dependent and the patch does not show attacker controlled reclaim, object replacement, type confusion, callback control, or write after free.

* **Real lifetime corruption: +1**
  The bug is a socket reference lifetime error. `bt_accept_dequeue()` drops the temporary reference too early, and `bt_accept_unlink()` can drop the final queue reference.

* **Reliable kernel crash / strong DoS: +1**
  KASAN observed freed memory access during listening L2CAP socket cleanup. Kernel crash is realistic.

* **Broad/common subsystem exposure: +1 paranoid only**
  Bluetooth is commonly available on desktop, laptop, and some embedded systems, but it is not universally enabled on server deployments.

Subtracted signals:

* **Hard or unreliable race / special timing required: -1**
  The issue depends on a narrow lifetime window between accept queue traversal, unlink, and concurrent teardown.

Not awarded:

* **Remote reachable / network trigger: +0**
  Bluetooth peer activity may contribute to L2CAP state, but reliable triggering appears to require local socket lifecycle control. This is not treated as normal remote network reachability.

* **Privilege escalation plausible: +0 conservative and paranoid**
  Although UAF is confirmed, the patch does not show reclaim control, stale object reuse, writable stale access, callback dispatch, or type confusion. Under the race UAF downgrade rule, this remains a weak primitive for ActionableScore.

* **Confidentiality / Integrity impact: +0**
  No readback, info leak, controlled overwrite, or practical corruption sink is demonstrated by the patch.

## 3. Reachability analysis

A local process that can create and manipulate Bluetooth L2CAP listening sockets is the most realistic trigger. The affected path is not ordinary IP networking and should not be scored as AV:N style remote reachability. A nearby Bluetooth peer may influence connection teardown timing, but the reliable trigger still appears to involve local control over the listening socket cleanup path.

Namespaces and containers may matter if Bluetooth socket access is delegated into a container or service sandbox. In typical deployments, Bluetooth access is more common on client or embedded systems than on hardened servers. Exploitation conditions are realistic for crash reproduction but not enough to infer reliable LPE.

Call-site confidence: **high**. The patch and commit message show the relevant caller behavior in `bt_accept_dequeue()` and `l2cap_sock_cleanup_listen()`.

## 4. Severity interpretation

This behaves above an ordinary Moderate because it is a confirmed kernel UAF in socket lifetime management. However, it does not reach a strong Important classification from the patch alone because the UAF is race dependent and no attacker controlled reuse, write primitive, type confusion, or callback hijack is shown.

Realistic impact is local DoS via kernel crash. Theoretical memory corruption risk exists because the object can be freed before later use, but exploitability beyond crash requires additional evidence.

## 5. One-sentence report phrase

A race dependent reference lifetime bug in Bluetooth L2CAP accept queue handling can cause `bt_accept_dequeue()` to access a freed socket during listening socket cleanup, leading to a local kernel crash with UAF based manual review relevance.

## 6. Manual review recommendation

**MANUAL CHECK REQUIRED**

Reason: confirmed UAF plus race/lifetime corruption in a socket subsystem. Even though the currently supported practical impact is DoS, UAF bugs should not be auto-closed without manual review.

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

Patch: Bluetooth: fix UAF in bt_accept_dequeue()
Commit: c0577c55219be42b6ea2ea8db11e85bfab6f4e8d
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=c0577c55219be42b6ea2ea8db11e85bfab6f4e8d

Commit description:

bt_accept_get() takes a temporary reference before dropping the accept
queue lock. bt_accept_dequeue() currently drops that reference before
bt_accept_unlink(), leaving only the queue reference.

bt_accept_unlink() drops the queue reference. The subsequent
sock_hold() therefore accesses freed memory if it was the final
reference, as observed by KASAN during listening L2CAP socket cleanup.

Retain the temporary queue-walk reference through unlink and hand it to
the caller on success. Drop it explicitly on the closed and
not-yet-connected paths.

Fixes: ab15135 ("Bluetooth: fix UAF in l2cap_sock_cleanup_listen() vs l2cap_conn_del()")
Reported-by: syzbot+674ff7e4d7fdfd572afc@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=674ff7e4d7fdfd572afc
Cc: stable@vger.kernel.org
Signed-off-by: Yousef Alhouseen <alhouseenyousef@gmail.com>
Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  net/bluetooth/af_bluetooth.c
  net/bluetooth/l2cap_sock.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=c0577c55219be42b6ea2ea8db11e85bfab6f4e8d

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

The original Linux kernel CVE announcement for CVE-2026-64406 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64406

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: 3
  Paranoid ActionableScore: 4

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: NO
Published priority for this report (same as in Subject): MODERATE REGULAR

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).