[CVE-2026-45835][MODERATE 7.0] Bluetooth: L2CAP: Fix null-ptr-deref in l2cap_sock_new_connection_cb()

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

CVE: CVE-2026-45835
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: Bluetooth: L2CAP: Fix null-ptr-deref in l2cap_sock_new_connection_cb()
Commit: ab77c8bc30269bee15d917059a66bea48909f5f0
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=ab77c8bc30269bee15d917059a66bea48909f5f0
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-45835
Analysis date: Tue, 26 May 2026 12:52:07 -0400
ActionableScore: 5
ActionableScore lower bound: 3
Actionable bucket: Actionable Moderate at minimum
Manual review required: NO

Summary:
A missing NULL check in Bluetooth L2CAP l2cap_sock_new_connection_cb can allow an adjacent Bluetooth peer to trigger a NULL pointer dereference and crash the kernel when the new connection callback is reached with chan data unset.

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ABOUT THIS REPORT
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The original Linux kernel CVE announcement for CVE-2026-45835 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-45835

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: NO

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-2026-45835	MODERATE	CHECK	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:A/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H';**CWE-476;CWE-754;CWE-703;Other CVSS 'AV:A/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '6.5';DESCR 'A NULL pointer dereference can occur in the Bluetooth L2CAP new connection callback because l2cap_sock_new_connection_cb calls lock_sock(parent) after reading parent from chan data without checking whether parent is NULL. An attacker in Bluetooth range may be able to trigger the vulnerable L2CAP path if the target has an exposed or reachable Bluetooth L2CAP service and the channel state reaches a missing parent socket condition. For the CVSS the PR:N is used because the attacker does not need a local account on the target and only needs Bluetooth adjacency to reach the protocol path. The issue is not directly reachable over the public Internet in the usual IP network sense. Impact is denial of service via kernel crash. C and I are not increased because this is a NULL pointer dereference without evidence of UAF, OOB write, or another memory corruption primitive.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate at minimum (with actual score 4)	YES	REMOTE NULLPTR SIMPLEFIX NETWORK  DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5	NO	NO	guess

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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. Bluetooth L2CAP is externally reachable over an adjacent wireless protocol when Bluetooth is enabled and the relevant L2CAP path is exposed.
* Reliable kernel crash / strong DoS: +1. The patch prevents lock_sock(parent) with parent == NULL, which is a direct NULL pointer dereference crash path.
* Availability impact realistic: +1. A kernel crash or oops is a realistic availability impact if the path is reachable.
* Hard or uncertain triggering condition: -1. The diff proves the missing NULL guard, but does not by itself prove that an unauthenticated peer can reliably force chan->data == NULL in common configurations.

Paranoid delta:

* No hard-race or timing penalty in the paranoid interpretation. If the L2CAP state can be reached by a malformed or unexpected connection sequence, triggering becomes a practical adjacent DoS.
* Broad/common subsystem exposure: +1. Bluetooth is a common kernel subsystem on laptops, desktops, and embedded systems, although not always enabled or listening.

Not counted:

* Generic memory corruption: +0. This is a NULL pointer dereference, not UAF, OOB write, double free, or type confusion.
* Privilege escalation plausible: +0. No reclaim, overwrite, refcount takeover, or object confusion primitive is shown.
* Confidentiality/Integrity: +0. No information leak or write primitive is supported by the patch.

## 3. Reachability analysis

The likely attacker is a nearby Bluetooth peer, not a local Linux user and not a public Internet attacker. PR:N is reasonable for CVSS-style thinking if the vulnerable L2CAP service is reachable because no local account on the victim is required. Practical reachability depends on Bluetooth being enabled, the host accepting or processing the relevant L2CAP connection path, and whether pairing or service exposure is required in the target deployment. Namespaces and containers are not the main factor here because the interesting attack surface is the host Bluetooth stack. The exploit condition is plausible but not fully demonstrated by the tiny patch, so the conservative score remains borderline while the paranoid score reaches actionable moderate.

## 4. Severity interpretation

This behaves like an adjacent-network denial-of-service issue rather than an Important-class memory corruption vulnerability. The theoretical risk is limited because the primitive is a NULL dereference and there is no evidence of UAF, controlled overwrite, page-cache corruption, or privilege escalation. However, Bluetooth is an external wireless attack surface, and a kernel crash reachable from a nearby peer should not be auto-closed without checking the exact L2CAP state machine and exposure requirements.

## 5. One-sentence report phrase

A missing NULL check in Bluetooth L2CAP l2cap_sock_new_connection_cb can allow an adjacent Bluetooth peer to trigger a NULL pointer dereference and crash the kernel when the new connection callback is reached with chan data unset.

## 6. Manual review recommendation

MANUAL CHECK RECOMMENDED

Reason: the bug is DoS-only based on the patch, but it is in an adjacent wireless protocol path with PR:N-style exposure when Bluetooth L2CAP is reachable. Manual review should confirm whether an unauthenticated or pre-pairing peer can reliably reach the missing-parent state.

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UPSTREAM PATCH SUMMARY
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Patch: Bluetooth: L2CAP: Fix null-ptr-deref in l2cap_sock_new_connection_cb()
Commit: ab77c8bc30269bee15d917059a66bea48909f5f0
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=ab77c8bc30269bee15d917059a66bea48909f5f0

Commit description:

Add the same NULL guard already present in
l2cap_sock_resume_cb() and l2cap_sock_ready_cb().

Fixes: 80808e4 ("Bluetooth: Add l2cap_chan_ops abstraction")
Cc: stable@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_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=ab77c8bc30269bee15d917059a66bea48909f5f0

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

The original Linux kernel CVE announcement for CVE-2026-45835 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-45835

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:H
  The Best / paranoid CVSS vector: AV:A/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS score: 6.5

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).