[CVE-2026-63976][MODERATE 7.0] Bluetooth: l2cap: clear chan->ident on ECRED reconfiguration success [ Upstream

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

CVE: CVE-2026-63976
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: Bluetooth: l2cap: clear chan->ident on ECRED reconfiguration success [ Upstream
Commit: 59f5ecf6ad5c4db6ae81965a96156954a3b0d89a
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=59f5ecf6ad5c4db6ae81965a96156954a3b0d89a
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-63976
Analysis date: Sun, 19 Jul 2026 13:04:31 -0400
ActionableScore: 5
ActionableScore lower bound: 3
Actionable bucket: Actionable Moderate at minimum
Manual review required: YES

Summary:
A Bluetooth L2CAP ECRED peer can replay a failure response after successful reconfiguration because chan ident remains stale, causing the kernel to delete an established channel, with a weak additional lifetime concern due to the refcount hardening in the same path.

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ABOUT THIS REPORT
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The original Linux kernel CVE announcement for CVE-2026-63976 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-63976

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-2026-63976	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-672;CWE-362;*CWE-416;Other CVSS 'AV:A/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '7.5';DESCR 'Bluetooth L2CAP ECRED reconfiguration can leave chan ident set after a successful response. A remote Bluetooth peer that already completed reconfiguration can replay a failure response with the stale ident and make the kernel match the established channel and delete it with ECONNRESET. For the CVSS the PR:N is used for the paranoid score because the trigger is performed by a remote Bluetooth peer and does not require local code execution on the target. The attack is adjacent network rather than Internet reachable because Bluetooth requires radio proximity or equivalent access. Base impact is denial of service for the affected L2CAP channel. The use of l2cap_chan_hold_unless_zero in the same path indicates a refcount lifetime hardening point, so the worst still defensible interpretation treats this as a possible remote adjacent UAF candidate requiring manual review.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate at minimum (with actual score 4)	YES	REMOTE SIMPLEFIX NETWORK  INCREASED_TO_HIGH_BASED_ON_GUESSCVSS DECREASED_TO_MODERATE70_BASED_ON_ACTIONABLESCORELOWERTHAN7 DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5	NO	NO	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=5
ActionableScoreLower=3

## 1. ActionableScore

* Conservative score: 3
* Paranoid score: 5
* Final recommended bucket: **Actionable Moderate at minimum**::

## 2. Signal breakdown

Conservative signals:

* Remote reachable / network-triggerable: +2. The trigger is from a remote Bluetooth L2CAP peer, but this is adjacent-network Bluetooth reachability, not routed Internet reachability.
* Availability impact realistic: +1. A peer can replay a failure response with a stale ident and cause deletion/reset of an already established L2CAP channel.

Conservative total: 3

Paranoid additional signals:

* Real lifetime corruption: +1. The patch also changes l2cap_chan_hold() to l2cap_chan_hold_unless_zero(), which indicates a lifetime/refcount hardening concern on the failure path.
* Memory corruption, weak/indirect corruption candidate: +1. The lifetime concern is not a demonstrated reclaim or write primitive, but it is enough to treat the path as a weak UAF/lifetime candidate for manual review.

Paranoid total: 5

Not counted:

* No strong LPE plausibility. The patch does not show attacker-controlled reclaim, controlled object replacement, callback control, arbitrary write, or type confusion.
* No strong generic memory corruption. The concrete demonstrated effect is channel deletion/reset, not a proven UAF exploit primitive.
* No hard race penalty. The replay condition is protocol-state based rather than a narrow timing-only race.
* No admin privilege penalty. The attacker is a Bluetooth peer and does not need local privileges on the target.

## 3. Reachability analysis

A remote Bluetooth peer that has completed ECRED reconfiguration can send a later failure response using the stale recycled ident. This makes the kernel match the response to an already established channel and call l2cap_chan_del(chan, ECONNRESET).

Privileges are effectively PR:N from the target-host perspective, because no local user account or local code execution is required. The exposure is adjacent-network only because Bluetooth requires radio proximity, pairing or connection context depending on deployment, and a reachable Bluetooth stack. Namespaces and containers do not materially reduce the attacker requirement because the trigger is external Bluetooth protocol traffic rather than a local namespace interface.

The path is not Internet-exposed, but Bluetooth is common enough on laptops, desktops, embedded devices, automotive systems, and IoT devices that this should not be auto-closed as a low-risk local-only issue.

Call-site confidence: medium. The relevant response handler and immediate deletion path are visible, but deeper channel lifetime behavior is inferred from the hold_unless_zero hardening and common L2CAP refcount patterns.

## 4. Severity interpretation

This behaves conservatively like an actionable adjacent-network DoS against Bluetooth L2CAP channels. The demonstrated primitive is stale transaction-state reuse leading to erroneous channel deletion.

The paranoid interpretation is stronger because the same patch hardens channel lifetime handling with l2cap_chan_hold_unless_zero(). That does not prove privilege escalation, but it raises enough UAF/refcount-lifetime concern to require manual review. Realistic exploitation evidence supports DoS. Theoretical memory-corruption potential is weak but not dismissible from the patch context.

## 5. One-sentence report phrase

A Bluetooth L2CAP ECRED peer can replay a failure response after successful reconfiguration because chan ident remains stale, causing the kernel to delete an established channel, with a weak additional lifetime concern due to the refcount hardening in the same path.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

Reason: the bug is adjacent-network reachable over Bluetooth, and although the concrete impact is channel DoS, the change from l2cap_chan_hold() to l2cap_chan_hold_unless_zero() indicates a possible refcount/lifetime hazard that should be reviewed manually before downgrading.

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UPSTREAM PATCH SUMMARY
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Patch: Bluetooth: l2cap: clear chan->ident on ECRED reconfiguration success [ Upstream
Commit: 59f5ecf6ad5c4db6ae81965a96156954a3b0d89a
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=59f5ecf6ad5c4db6ae81965a96156954a3b0d89a

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=59f5ecf6ad5c4db6ae81965a96156954a3b0d89a

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

The original Linux kernel CVE announcement for CVE-2026-63976 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-63976

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:L/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: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: 3
  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: NO
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).