[CVE-2026-98108][MODERATE 7.0] Bluetooth: L2CAP: fix chan mode for LE_CONN_REQ + EXT_FLOWCTL pchan [ Upstream

[CVE-2026-98108][MODERATE 7.0] Bluetooth: L2CAP: fix chan mode for LE_CONN_REQ + EXT_FLOWCTL pchan [ Upstream

[AL-KERNEL]

CVE: CVE-2026-98108
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: Bluetooth: L2CAP: fix chan mode for LE_CONN_REQ + EXT_FLOWCTL pchan [ Upstream
Commit: 1074bcc57f741223f9fa82ce6afe5c3d783e4d10
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=1074bcc57f741223f9fa82ce6afe5c3d783e4d10
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98108
Analysis date: Fri, 25 Sep 2026 08:34:02 -0400
ActionableScore: 5
ActionableScore lower bound: unknown
Actionable bucket: Actionable Moderate / Strong Important candidate requiring manual review
Manual review required: YES

Summary:
No one-sentence report phrase was found.

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

The original Linux kernel CVE announcement for CVE-2026-98108 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98108

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.

======================================================================
AL-KERNEL CLASSIFICATION RESULT
======================================================================

CVE-2026-98108	MODERATE	https://www.kernelcve.org/list/?q=CVE-2026-98108 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-787;*CWE-20;CWE-665;Other CVSS 'AV:A/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:H';BEST CVSS score: '7.5';DESCR 'An incorrect channel mode can cause an LE_CONN_REQ channel to inherit L2CAP_MODE_EXT_FLOWCTL from its listening parent instead of using L2CAP_MODE_LE_FLOWCTL. With deferred setup enabled, crafted or repeated Bluetooth LE connection requests can reach l2cap_ecred_rsp_defer() through the wrong protocol path. Missing limits on deferred channels and missing duplicate ident validation can then increase rsp count beyond the dcid array and cause a stack out of bounds write in kernel context. For the CVSS the PR:N is selected because a nearby Bluetooth peer does not need an account or local privileges on the target. AV:A is used because exploitation requires Bluetooth radio proximity and access to the affected L2CAP service rather than routable network access. AC:H reflects the required listening channel configuration, deferred setup state, and crafted request sequence. Impact is at least denial of service through kernel memory corruption. In the paranoid case the stack write may affect confidentiality and integrity or permit kernel code execution, although a reliable arbitrary write primitive is not established by the supplied code.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate / Strong Important candidate requiring manual review (with actual score 5)  SKIP CVE-2026-98108 UNKNOWN SKIP The Fixes patch not applied yet, so unlikely that actual: url YES  NO NO unknown 	MAYBE	REMOTE WRITE OOB DANGER SIMPLEFIX NETWORK KPANIC  KPANIC INCREASED_TO_HIGH_BASED_ON_GUESSCVSS DECREASED_TO_MODERATE7_BASED_ON_FALSEPOSCHECKOFKP	-	-	checked

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

ActionableScore=5
PrimitiveClass=CLASS_A
RealUAF=NO
HostAdminRequired=NO
NamespaceScopedPrivilege=NO
ImportantCandidate=YES
ManualReview=REQUIRED
AutoDowngradeAllowed=NO

1. ActionableScore

* Raw conservative score: 5
* Conservative score: 5
* Raw paranoid score: 5
* Paranoid score: 5
* No floor or cap was applied.
* Final recommended bucket: **Actionable Moderate / Strong Important candidate requiring manual review**::

2. Signal breakdown

* +2 Strong corruption primitive. The patch explicitly establishes a stack OOB write in `l2cap_ecred_rsp_defer()`. A nearby peer influences the number and grouping of deferred channels through LE connection requests and duplicate identifiers.
* +2 Direct adjacent-network reachability. Bluetooth LE requests from a nearby peer reach the vulnerable L2CAP operation without requiring an account or privileges on the target.
* +1 Reliable kernel crash or strong DoS. An out-of-bounds stack write in kernel context realistically supports an Oops, panic, or corrupted control flow.
* No timing penalty. This is a protocol-state and bounds-validation defect, not a race.
* No rare-hardware penalty. Bluetooth hardware is required, but the supplied evidence does not establish rare or physical-console-only hardware.
* No separate Strong LPE bonus. The destination is adjacent stack storage and the index is influenced, but neither an arbitrary target nor sufficiently controlled payload is established.
* No C or I bonus. Corruption is concrete, but protected-data disclosure, persistent unauthorized state modification, or a complete privilege-escalation chain is not demonstrated.
* No extra Availability point. The possible crash is already counted.
* Controlled reclaim, arbitrary kernel read or write, callback control, and demonstrated code execution are not established.

3. Reachability analysis

A nearby unauthenticated Bluetooth LE peer can send LE connection requests to an affected listening L2CAP service. The vulnerable configuration requires a listening parent channel using `L2CAP_MODE_EXT_FLOWCTL` and deferred setup. This is a target-side service prerequisite, but the remote attacker does not need host-admin privilege to transmit the triggering requests.

The attacker can influence duplicate identifiers and the number of deferred channels, causing `rsp->count` to reach or exceed the `dcid` array bound. No namespace capability is part of the remote trigger. No race is involved, and repeated attempts appear practical while the affected service remains reachable.

4. Primitive and severity interpretation

The exact primitive is an attacker-influenced stack OOB write of `l2cap_alloc_cid()` determined channel identifiers. The channel incorrectly inherits `L2CAP_MODE_EXT_FLOWCTL`, causing an ordinary `LE_CONN_REQ` deferred channel to be processed as an ECRED channel. Missing duplicate-ident and deferred-channel limits then permit an out-of-range `dcid[rsp->count++]` write.

This is not a UAF or repeated lifetime operation. It is CLASS_A because a concrete, remotely influenced kernel stack overwrite is directly established. The demonstrated practical consequence is memory corruption with plausible kernel DoS. Code execution or privilege escalation remains a technically relevant review question, but is not established because payload and destination control are constrained.

ImportantCandidate is YES because automatic Moderate downgrading would discard a concrete adjacent-network kernel stack corruption primitive. AutoDowngradeAllowed is NO for the same reason.

5. One-sentence report phrase

A nearby Bluetooth LE peer can exploit incorrect L2CAP channel mode inheritance and missing deferred-channel bounds checks to trigger a kernel stack out-of-bounds write, requiring manual review for impact beyond denial of service.

6. Manual review recommendation

MANUAL CHECK REQUIRED

The patch establishes remotely influenced kernel stack corruption, while the exact overwritten stack fields and resulting exploitation leverage require surrounding-layout and runtime analysis.

7. Call-site confidence

Call-site confidence: medium

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

Patch: Bluetooth: L2CAP: fix chan mode for LE_CONN_REQ + EXT_FLOWCTL pchan [ Upstream
Commit: 1074bcc57f741223f9fa82ce6afe5c3d783e4d10
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=1074bcc57f741223f9fa82ce6afe5c3d783e4d10

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=1074bcc57f741223f9fa82ce6afe5c3d783e4d10

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

The original Linux kernel CVE announcement for CVE-2026-98108 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98108

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:L/I:L/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: 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).