[CVE-2026-63975][MODERATE 7.0] Bluetooth: L2CAP: Fix possible crash on l2cap_ecred_conn_rsp [ Upstream

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

CVE: CVE-2026-63975
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: Bluetooth: L2CAP: Fix possible crash on l2cap_ecred_conn_rsp [ Upstream
Commit: 3c8eaa91eb433c450426539290be4ffe282e9f00
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=3c8eaa91eb433c450426539290be4ffe282e9f00
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-63975
Analysis date: Sun, 19 Jul 2026 22:16:49 -0400
ActionableScore: 6
ActionableScore lower bound: 5
Actionable bucket: Actionable Moderate at minimum
Manual review required: YES

Summary:
A nearby Bluetooth peer may trigger a kernel crash by sending an L2CAP ECred connection response with a duplicate destination CID, causing unsafe channel deletion during list traversal and a possible stale cursor or UAF candidate.

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ABOUT THIS REPORT
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The original Linux kernel CVE announcement for CVE-2026-63975 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-63975

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-2026-63975	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-672;*CWE-664;Other CVSS 'AV:A/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '7.5';DESCR 'A Bluetooth L2CAP ECred response can contain a Destination CID that is already assigned to another channel. The old handling path could delete channels while iterating over conn chan_l, which may invalidate the saved list cursor and lead to a use-after-free candidate or kernel crash. A nearby Bluetooth peer can trigger this by sending a crafted L2CAP_CREDIT_BASED_CONNECTION_RSP with a duplicate dcid during ECred setup. For the CVSS the PR:N is used because no local account or kernel privilege is required on the victim, only Bluetooth adjacency and protocol reachability are needed. The base impact is denial of service via kernel crash. The paranoid impact is raised to C:H/I:H/A:H because the patch context indicates deletion of list elements during iteration and a possible stale pointer use in kernel memory, which deserves manual review for privilege escalation risk.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate at minimum (with actual score 6)	YES	REMOTE DANGER INIT NETWORK KERNEL_PANIC_PLUS_UAF TIMER HARDWARE KPANIC PACKET  KPANIC INCREASED_TO_HIGH_BASED_ON_GUESSCVSS KPANIC DECREASED_TO_MODERATE70_BASED_ON_ACTIONABLESCORELOWERTHAN7	NO	NO	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=6
ActionableScoreLower=5

## 1. ActionableScore

* Conservative score: 5
* Paranoid score: 6
* Final recommended bucket: **Actionable Moderate at minimum**::

## 2. Signal breakdown

Conservative signals:

* Remote reachable / network-triggerable: +2
  Bluetooth is adjacent-network rather than Internet-reachable, but a nearby Bluetooth peer can influence the affected L2CAP ECred response path.

* Memory corruption, weak/indirect corruption candidate: +1
  The patch prevents deleting a channel while iterating over `conn->chan_l`, which may invalidate the `tmp` cursor from `list_for_each_entry_safe`. This is a stale-list-cursor / UAF-candidate pattern, but no controlled reclaim or overwrite primitive is shown.

* Real lifetime corruption: +1
  `l2cap_chan_del()` can remove or invalidate channel lifetime state while traversal is still in progress.

* Reliable kernel crash / strong DoS: +1
  The commit explicitly describes a possible crash, and the fix avoids a synchronous deletion path that can corrupt iteration state.

Paranoid additional signal:

* Weak LPE concern: +1
  A stale list cursor over `struct l2cap_chan` objects could theoretically become more than a crash if object reuse is reachable, but the patch does not demonstrate attacker-controlled reclaim, callback control, arbitrary write, or reliable object replacement.

Not applied:

* Strong LPE plausibility: +0
  No demonstrated reclaim, overwrite, type confusion, callback dispatch, or refcount takeover.

* Confidentiality / Integrity impact: +0 conservative
  The realistic evidence supports crash/lifetime corruption, not a concrete read or write primitive.

* Hard race penalty: 0
  This is not mainly a timing race. It is a protocol-triggered invalid deletion during list traversal.

## 3. Reachability analysis

A nearby Bluetooth peer can potentially trigger the bug by sending an L2CAP Enhanced Credit Based Connection Response with a duplicate already-assigned destination CID during ECred setup. No local user account on the victim is required, so the practical privilege level is PR:N in CVSS terms. This is not Internet-reachable and requires Bluetooth adjacency, Bluetooth enabled, and a reachable L2CAP path. Namespaces and containers do not materially lower or raise the privilege requirement because the trigger is external Bluetooth protocol input rather than a local namespace-controlled API.

Call-site confidence: high. The relevant loop, deletion calls, and replacement asynchronous timeout behavior are visible in the provided patch.

## 4. Severity interpretation

This behaves as an actionable Moderate issue under conservative triage because it is externally triggerable over Bluetooth adjacency and involves a real kernel object lifetime/list-iteration hazard. It is not merely a validation cleanup or local privileged control-plane bug. The realistic impact is kernel crash / DoS.

The paranoid interpretation reaches manual-review territory because deletion during list traversal can produce a UAF-candidate pattern in kernel memory. However, the patch does not show a strong exploitation primitive, so it should not be treated as a proven Important-class LPE without further analysis.

## 5. One-sentence report phrase

A nearby Bluetooth peer may trigger a kernel crash by sending an L2CAP ECred connection response with a duplicate destination CID, causing unsafe channel deletion during list traversal and a possible stale cursor or UAF candidate.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

Reason: externally triggerable Bluetooth parsing plus kernel lifetime/list corruption is enough to avoid auto-close, even though the demonstrated impact is DoS and no reliable privilege-escalation primitive is proven.

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

Patch: Bluetooth: L2CAP: Fix possible crash on l2cap_ecred_conn_rsp [ Upstream
Commit: 3c8eaa91eb433c450426539290be4ffe282e9f00
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=3c8eaa91eb433c450426539290be4ffe282e9f00

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=3c8eaa91eb433c450426539290be4ffe282e9f00

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

The original Linux kernel CVE announcement for CVE-2026-63975 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-63975

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: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: 5
  Paranoid ActionableScore: 6

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).