[CVE-2026-63948][MODERATE REGULAR] Bluetooth: L2CAP: fix chan ref leak in l2cap_chan_timeout() on !conn

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

CVE: CVE-2026-63948
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: Bluetooth: L2CAP: fix chan ref leak in l2cap_chan_timeout() on !conn
Commit: 50f1bcaaaa3a80bb1c3472044bc146e8d49d51ee
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=50f1bcaaaa3a80bb1c3472044bc146e8d49d51ee
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-63948
Analysis date: Sun, 19 Jul 2026 22:53:56 -0400
ActionableScore: 4
ActionableScore lower bound: 3
Actionable bucket: Borderline manual review recommended / Ordinary Moderate likely
Manual review required: YES

Summary:
Bluetooth L2CAP can leak a channel reference in `l2cap_chan_timeout()` when the connection pointer is already NULL, allowing a nearby Bluetooth peer in some configurations to cause repeated resource leaks and potential denial of service.

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ABOUT THIS REPORT
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The original Linux kernel CVE announcement for CVE-2026-63948 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-63948

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-2026-63948	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:N/I:N/A:H';*CWE-772;*CWE-401;CWE-404;Other CVSS 'AV:A/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '5.3';DESCR 'Bluetooth L2CAP can leak a channel reference in l2cap_chan_timeout when the timeout work runs after the channel has no connection object. The timer setup path holds a channel reference before scheduling delayed work, but the early return on a NULL conn skips the matching put and leaves the channel object referenced. A nearby Bluetooth peer may be able to contribute to repeated channel setup teardown and timeout conditions if the host exposes L2CAP over Bluetooth. For the CVSS the PR:N is used in the paranoid score because triggering may only require adjacent Bluetooth reachability and no local account on the victim. Impact is resource exhaustion and denial of service if the leak can be repeated. No memory corruption or privilege escalation primitive is shown by the patch context.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline manual review recommended / Ordinary Moderate likely (with actual score 4)	YES	REMOTE NULLPTR SIMPLEFIX LEAK NETWORK  DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5	YES	NO	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 / Ordinary Moderate likely**

## 2. Signal breakdown

Conservative signals:

* Adjacent network reachable Bluetooth surface: +1
  Bluetooth L2CAP can be influenced by a nearby Bluetooth peer if the host has Bluetooth enabled and discoverable or connectable enough for the relevant L2CAP flow.
* Real lifetime / refcount bug: +1
  `__set_chan_timer()` takes a `l2cap_chan` reference, and the early `!conn` return path failed to drop it.
* Availability impact plausible: +1
  Repeated leaked channel references can cause resource retention and eventual DoS.

Paranoid additional signal:

* Potential repeated resource exhaustion: +1
  If a nearby attacker can repeatedly force channel setup / teardown / timeout states, the leak may become a practical memory/resource exhaustion vector.

Negative / non-applied signals:

* Hard or state-dependent timing: -1 considered but not applied in the paranoid score because the timeout/teardown pattern may be naturally reachable under repeated connection churn.
* No generic memory corruption: +0
  This is a reference leak, not UAF, double-free, OOB write, type confusion, or arbitrary write.
* No privilege escalation plausible: +0
  The patch does not show reclaim, stale object reuse, callback control, write-after-free, or object confusion.
* No confidentiality or integrity impact: +0
  The primitive is retained references / resource leak only.

## 3. Reachability analysis

A nearby Bluetooth peer may be able to influence L2CAP channel lifecycle and timeout behavior, so the practical attack surface is adjacent wireless rather than Internet remote. No local account on the victim is necessarily required if the Bluetooth stack exposes the relevant L2CAP behavior to the peer. Bluetooth is common on desktops, laptops, phones, and embedded devices, but often absent or disabled on servers, so exposure is deployment-dependent. The bug requires repeated or well-timed channel timeout conditions with `chan->conn == NULL`, which makes exploitation less straightforward than a single-packet crash.

Call-site confidence: medium. The patch and commit message clearly describe the reference acquisition and missing release path, but do not include a full reproducer or all caller paths.

## 4. Severity interpretation

This behaves more like an ordinary Moderate / borderline actionable Moderate than an Important-class vulnerability. The realistic impact is resource exhaustion DoS from a leaked `l2cap_chan` reference. The theoretical risk does not extend to memory corruption or privilege escalation based on the patch context, because the object is kept alive too long rather than freed too early. Manual review is still useful because Bluetooth L2CAP is an adjacent attack surface and repeatability determines whether the availability impact is minor or practically significant.

## 5. One-sentence report phrase

Bluetooth L2CAP can leak a channel reference in `l2cap_chan_timeout()` when the connection pointer is already NULL, allowing a nearby Bluetooth peer in some configurations to cause repeated resource leaks and potential denial of service.

## 6. Manual review recommendation

MANUAL CHECK RECOMMENDED

Reason: the bug is not a strong memory-corruption or LPE candidate, but it is in an adjacent-network Bluetooth protocol path and the practical severity depends on whether an unauthenticated or low-interaction nearby peer can repeatedly trigger the leaking timeout state.

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

Patch: Bluetooth: L2CAP: fix chan ref leak in l2cap_chan_timeout() on !conn
Commit: 50f1bcaaaa3a80bb1c3472044bc146e8d49d51ee
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=50f1bcaaaa3a80bb1c3472044bc146e8d49d51ee

Commit description:

__set_chan_timer() takes a l2cap_chan reference via l2cap_chan_hold()
before scheduling the delayed work.  The normal path in
l2cap_chan_timeout() drops this reference with l2cap_chan_put() at the
end, but the early return when chan->conn is NULL skips the put,
leaking the reference.

Add the missing l2cap_chan_put() before the early return.

Fixes: adf0398 ("Bluetooth: l2cap: fix null-ptr-deref in l2cap_chan_timeout")
Cc: stable@vger.kernel.org
Signed-off-by: Siwei Zhang <oss@fourdim.xyz>
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/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=50f1bcaaaa3a80bb1c3472044bc146e8d49d51ee

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

The original Linux kernel CVE announcement for CVE-2026-63948 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-63948

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:N/I:N/A:L
  The Best / paranoid CVSS vector: AV:A/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS score: 5.3

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).