[CVE-2026-53357][MODERATE 7.0] Bluetooth: fix UAF in l2cap_sock_cleanup_listen() vs l2cap_conn_del() [ Upstream

[CVE-2026-53357][MODERATE 7.0] Bluetooth: fix UAF in l2cap_sock_cleanup_listen() vs l2cap_conn_del() [ Upstream

[AL-KERNEL]

CVE: CVE-2026-53357
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: Bluetooth: fix UAF in l2cap_sock_cleanup_listen() vs l2cap_conn_del() [ Upstream
Commit: 751de6ec671fe75ad9cf65a0638d2a06b6a5984d
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=751de6ec671fe75ad9cf65a0638d2a06b6a5984d
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53357
Analysis date: Thu, 02 Jul 2026 09:56:43 -0400
ActionableScore: 5
ActionableScore lower bound: 4
Actionable bucket: Strong Important candidate / Actionable Moderate at minimum
Manual review required: YES

Summary:
A confirmed Bluetooth L2CAP race can let an unprivileged local process trigger a use-after-free between listening socket cleanup and HCI disconnect teardown, causing a kernel crash and requiring manual review for possible UAF-based escalation risk.

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

The original Linux kernel CVE announcement for CVE-2026-53357 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53357

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
======================================================================

CVE-2026-53357	MODERATE	CHECK	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 use after free exists in the Bluetooth L2CAP listen cleanup path because bt_accept_dequeue can return a child socket without a stable caller reference after unlinking it from the accept queue. A concurrent HCI disconnect can run through hci_rx_work and l2cap_conn_del, free the child socket and its l2cap_chan, and leave l2cap_sock_cleanup_listen using freed objects during listening socket close. For the CVSS the PR:L is used because a local unprivileged process can exercise the Bluetooth socket listen and close path while the disconnect race is triggered. The issue is not scored as directly network reachable because the patch context still requires local socket activity, although a nearby Bluetooth peer may help drive the disconnect side of the race. Impact is at least local denial of service via kernel crash and in the paranoid case may allow confidentiality and integrity impact due to kernel use after free memory corruption. YES REQUIRES MANUAL CHECK.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 5)	YES	REMOTE DEADLOCK DANGER INIT RACE UAF NETWORK KPANIC 	NO	NO	checked

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

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

Conservative signals:

* Local unprivileged trigger: +1
  The commit states that an unprivileged listen/close race can reproduce the issue.

* Memory corruption, weak primitive: +1
  This is a confirmed KASAN slab use-after-free involving `struct sock` and `l2cap_chan`, but the patch does not show attacker-controlled reclaim, type confusion, arbitrary write, or callback control.

* Real lifetime corruption: +1
  The bug is a reference/lifetime race where `bt_accept_dequeue()` returns a child socket without a stable caller reference, while `l2cap_conn_del()` can free the same socket and channel.

* Reliable kernel crash / strong DoS: +1
  The commit includes a KASAN UAF trace and says the race produced multiple UAF reports per run before the fix.

Paranoid additional signal:

* Firmware-mediated or adjacent external influence: +1
  The freeing side is driven by an HCI disconnect path. This is not scored as fully remote reachable, but a nearby Bluetooth peer or controller event may help trigger the disconnect side of the race.

Not awarded:

* No Remote reachable / network-triggerable +2
  The patch context still requires local socket activity and does not establish a purely remote attack.

* No strong LPE +2
  The UAF is real, but the patch does not demonstrate controlled reclaim, stale callback dispatch, arbitrary write, refcount takeover, or attacker-controlled object replacement.

* No hard race penalty
  Although this is a race, the commit reports repeated KASAN reproductions under SMP testing, so it is not treated as merely theoretical or extremely unreliable.

## 3. Reachability analysis

A local unprivileged process can exercise the Bluetooth L2CAP listening socket close path. The competing teardown path is triggered by an HCI disconnect through `hci_rx_work -> l2cap_conn_del()`. This makes the bug local in CVSS-style terms, with possible adjacent Bluetooth assistance, but not a clear network-only remote trigger.

Namespaces and containers may matter if Bluetooth socket access is delegated or exposed to less trusted workloads. In typical desktop or embedded systems with Bluetooth enabled, the subsystem is realistic. On servers without Bluetooth hardware or with Bluetooth disabled, exposure is much lower.

Call-site confidence: high. The patch shows both the vulnerable caller path and the reference-handling changes in `bt_accept_dequeue()`, L2CAP cleanup, and related Bluetooth accept users.

## 4. Severity interpretation

This is more than an ordinary Moderate because it is a confirmed kernel UAF in socket/channel lifetime handling and is reproducible with unprivileged local activity. Realistically, the demonstrated impact is kernel crash or DoS. Theoretical privilege escalation concern exists because the affected objects are kernel heap objects with lifetime corruption, but the patch does not show a concrete exploit primitive beyond UAF.

Conservative handling is Actionable Moderate. Paranoid handling reaches Strong Important candidate / Actionable Moderate at minimum because kernel UAFs in reachable local protocol code should not be auto-closed without manual review.

## 5. One-sentence report phrase

A confirmed Bluetooth L2CAP race can let an unprivileged local process trigger a use-after-free between listening socket cleanup and HCI disconnect teardown, causing a kernel crash and requiring manual review for possible UAF-based escalation risk.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

Reason: confirmed KASAN use-after-free, local unprivileged trigger, socket/channel lifetime corruption, and possible adjacent Bluetooth influence. The known impact is DoS, but kernel UAF class and reachable local trigger make automatic closure unsafe.

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

Patch: Bluetooth: fix UAF in l2cap_sock_cleanup_listen() vs l2cap_conn_del() [ Upstream
Commit: 751de6ec671fe75ad9cf65a0638d2a06b6a5984d
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=751de6ec671fe75ad9cf65a0638d2a06b6a5984d

Changed files:
  net/bluetooth/af_bluetooth.c
  net/bluetooth/l2cap_sock.c
  net/bluetooth/rfcomm/sock.c
  net/bluetooth/sco.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=751de6ec671fe75ad9cf65a0638d2a06b6a5984d

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

The original Linux kernel CVE announcement for CVE-2026-53357 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53357

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).