[CVE-2026-99239][MODERATE 7.0] Bluetooth: L2CAP: refuse __l2cap_chan_add if chan already has conn [ Upstream

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

CVE: CVE-2026-99239
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: Bluetooth: L2CAP: refuse __l2cap_chan_add if chan already has conn [ Upstream
Commit: 85cc289eb08afa975375f838187369e68b429ee0
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=85cc289eb08afa975375f838187369e68b429ee0
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-99239
Analysis date: Mon, 02 Nov 2026 22:22:09 -0400
ActionableScore: 5
ActionableScore lower bound: unknown
Actionable bucket: Actionable Moderate / Strong Important candidate requiring manual review
Manual review required: YES

Summary:
A local L2CAP bind/connect race can add one live channel twice, corrupting connection/linkage state later trusted by channel cleanup and traversal.

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

The original Linux kernel CVE announcement for CVE-2026-99239 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-99239

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-2026-99239	MODERATE	https://www.kernelcve.org/list/?q=CVE-2026-99239 CHECK WITH IMPACT FROM ORIG NN IMPORTANT | AEGIS IMPACT MODERATE_KPANIC AEGIS_AS=1 LEGACY=MODERATE_KPANIC RESULT=SAME (final reconciliation agrees; DECISION: both MODERATE_KPANIC)	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-362;*CWE-416;*CWE-672;*CWE-664;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:H';BEST CVSS score: '7';DESCR 'A TOCTOU race between l2cap_chan_connect and l2cap_sock_bind can change chan state and allow a second __l2cap_chan_add for the same L2CAP channel. Readding the same intrusive channel object violates connection lifetime and list invariants and can leave l2cap_chan_del or later list traversal operating on corrupted linkage or stale references. This creates a plausible UAF or invalid list dereference path with kernel crash as the clearest impact and possible confidentiality or integrity impact from memory corruption. For the CVSS the PR:L value is selected because a local unprivileged process must operate a Bluetooth L2CAP socket and race bind against connect. AC:H reflects the required timing window. The issue is not directly remotely reachable although a usable Bluetooth stack and connection path are prerequisites. Automated impact decision path. The original SimpleNet classifier selected IMPORTANT. The primary LLM estimated paranoid CVSS 7 and the production ActionableScore returned 5 with recommendation Actionable Moderate / Strong Important candidate requiring manual review. The production rules then evaluated CVSS thresholds and ActionableScore thresholds. Recorded rule transitions were KP and FD specialist checks stage IMPORTANT to MODERATE_KPANIC because a specific evidence based protection or manual review veto was applied and FD false positive review allowed a downgrade. The legacy KP specialist produced a review artifact and its decision was processed by the applicable KP rules. The legacy FD or DH downgrade specialist produced a review artifact and its decision was processed by the applicable downgrade and preservation rules. Exact triggered rule markers were V33_ACTIVE_STATE_BOUNDARY_CANDIDATE and IMPORTANT_CANDIDATE_MANUAL_REVIEW and KP_ONLY_DOWNGRADE_VETO and DECREASED_TO_MODERATE7_BASED_ON_FALSEPOSCHECKOFDH. The independent weaker Aegis shadow evaluated CVSS 2.7 and ActionableScore 1 with primitive class CLASS_B and manual review REQUIRED. Its independently reconciled impact was MODERATE_KPANIC. The shadow agreed with the final production impact and aggregation did not change that impact. The final reported impact is MODERATE_KPANIC.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate / Strong Important candidate requiring manual review (with actual score 5)	MAYBE	REMOTE WRITE OOB RACE LEAK UAF NETWORK LINUS TEST KPANIC  V33_ACTIVE_STATE_BOUNDARY_CANDIDATE IMPORTANT_CANDIDATE_MANUAL_REVIEW KP_ONLY_DOWNGRADE_VETO DECREASED_TO_MODERATE7_BASED_ON_FALSEPOSCHECKOFDH	-	-	checked

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

ActionableScore=5
PrimitiveClass=CLASS_B
RealUAF=NO
HostAdminRequired=NO
NamespaceScopedPrivilege=NO
ImportantCandidate=YES
ManualReview=REQUIRED
AutoDowngradeAllowed=NO
RequiresHostUID0=NO
AuthorizationDecisionBypass=NO
ProtectedResourceImpact=NONE
B4PendingReview=NO
B4PendingConfirmed=NO

1. ActionableScore

* Raw base score: 4.
* Conservative score: 5. Applied the manual-review safety floor, 4 -> 5, because attacker-influenced active structured state is linked twice and later consumed by privileged cleanup/list processing.
* Raw paranoid score: 4.
* Paranoid score: 5, using the same safety floor; no speculative exploit bonus was added.
* Final recommended bucket: **Actionable Moderate / Strong Important candidate requiring manual review**::

2. Signal breakdown

* +2 concrete active-object corruption: the race permits a second `__l2cap_chan_add()` on the same channel, violating the single-connection/linkage invariant and rewriting active connection/list state.
* +1 local unprivileged trigger: ordinary L2CAP socket `bind()`/`connect()` operations can drive the two racing paths; no capability check or host-admin prerequisite is shown.
* +1 plausible kernel crash/DoS: the commit explicitly identifies later `l2cap_chan_del` cleanup and other consumers as relying on the violated invariant.
* No timing penalty: a race exists, but the attacker controls both socket operations and can retry; the patch does not establish a one-shot or externally uncontrollable window.
* No UAF score: stale post-free use is only plausible in the legacy summary, not established by the patch.
* No controlled reclaim, arbitrary write, disclosure, or C/I impact is shown. The same possible crash was not counted again as Availability.
* B5-R does not apply: there is no retry-accumulated heap OOB write. B4-PENDING does not apply because no authorization decision changes from DENY to ALLOW.

3. Reachability analysis

A local process able to create and operate an L2CAP socket can race `bind()` against `connect()` on the same channel. Bluetooth availability and a usable connection path are prerequisites, but no host UID 0, capability, prior privileged setup, or special namespace privilege is evidenced. This is not directly remote reachability. Repeated attempts appear practical, although successful interleaving remains timing-dependent.

4. Primitive and severity reading

The primitive is duplicate insertion/association of one live `l2cap_chan` into connection state. It corrupts active structured linkage and connection ownership assumptions; later privileged cleanup consumes that state. This is CLASS_B object/list corruption, not a confirmed UAF and not CLASS_A because no directed target, controlled replacement, callback influence, or reusable write primitive is shown.

The non-crash exploit effect remains unknown. ImportantCandidate is YES under the active-state/trust-boundary rule: attacker-influenced active corruption, a concrete later privileged consumer, and the unprivileged-socket-to-kernel boundary are separately grounded. Auto-downgrade is therefore unsafe despite the absence of proven LPE.

5. One-sentence report phrase

A local L2CAP bind/connect race can add one live channel twice, corrupting connection/linkage state later trusted by channel cleanup and traversal.

6. Manual review advice

MANUAL CHECK REQUIRED

Review the complete `__l2cap_chan_add` linkage writes and all `l2cap_chan_del`/list consumers for post-corruption lifetime mutation, stale-reference use, and exploit leverage beyond the plausible crash.

7. Call-site confidence

Call-site confidence: medium

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

Patch: Bluetooth: L2CAP: refuse __l2cap_chan_add if chan already has conn [ Upstream
Commit: 85cc289eb08afa975375f838187369e68b429ee0
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=85cc289eb08afa975375f838187369e68b429ee0

Changed files:
  net/bluetooth/l2cap_core.c
  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=85cc289eb08afa975375f838187369e68b429ee0

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

The original Linux kernel CVE announcement for CVE-2026-99239 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-99239

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: unknown
  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).