[CVE-2026-98736][MODERATE 7.0] Bluetooth: hci_conn: Lock parent access during enhanced SCO setup

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

CVE: CVE-2026-98736
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: Bluetooth: hci_conn: Lock parent access during enhanced SCO setup
Commit: 1239ef0fa809b5952fca679db3faa3e1c00e1dac
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=1239ef0fa809b5952fca679db3faa3e1c00e1dac
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98736
Analysis date: Sat, 24 Oct 2026 09:01:06 -0400
ActionableScore: 4
ActionableScore lower bound: unknown
Actionable bucket: Borderline / manual review recommended
Manual review required: YES

Summary:
A narrow Bluetooth workqueue race permits a demonstrated one-byte read from a freed ACL parent during SCO parameter selection, plausibly crashing the kernel without a shown write or reuse primitive.

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ABOUT THIS REPORT
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The original Linux kernel CVE announcement for CVE-2026-98736 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98736

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-2026-98736	MODERATE	https://www.kernelcve.org/list/?q=CVE-2026-98736 CHECK WITH IMPACT FROM ORIG NN MODERATE | AEGIS IMPACT MODERATE_KPANIC AEGIS_AS=5 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:L/I:L/A:H';*CWE-416;CWE-362;CWE-667;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '5.8';DESCR 'A race in hci_enhanced_setup_sync allows the receive workqueue to unlink and free the ACL parent while the request workqueue still uses a previously loaded conn parent pointer. The demonstrated primitive is a one byte slab use after free read from parent features during enhanced SCO parameter selection. A local attacker able to initiate SCO activity may trigger a kernel crash by racing setup against ACL disconnection. A Bluetooth peer may help control disconnection timing, but the available evidence does not establish a fully remote trigger lacking a local SCO consumer. For the CVSS the PR:L value reflects the need for a local user or process able to reach Bluetooth SCO operations. AC:H reflects the required workqueue interleaving and narrow lifetime window. Availability impact is high due to a possible kernel crash. Limited confidentiality or integrity impact is retained only in the paranoid vector because slab reuse could influence the stale capability read, while no arbitrary write or reliable information disclosure is demonstrated. Automated impact decision path. The original SimpleNet classifier selected MODERATE_KPANIC. The primary LLM estimated paranoid CVSS 5.8 and the production ActionableScore returned 4 with recommendation Borderline / manual review recommended. The production rules then evaluated CVSS thresholds and ActionableScore thresholds. No severity changing production threshold or specialist override was recorded. 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 has no review artifact for this run. The independent weaker Aegis shadow evaluated CVSS 2.5 and ActionableScore 5 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 Borderline / manual review recommended (with actual score 4)	MAYBE	REMOTE READ OOB DANGER UAF NETWORK HARDWARE LINUS KPANIC 	-	-	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=4
PrimitiveClass=CLASS_B
RealUAF=YES
HostAdminRequired=UNKNOWN
NamespaceScopedPrivilege=UNKNOWN
ImportantCandidate=NO
ManualReview=RECOMMENDED
AutoDowngradeAllowed=YES
RequiresHostUID0=UNKNOWN
AuthorizationDecisionBypass=NO
ProtectedResourceImpact=NONE
B4PendingReview=NO
B4PendingConfirmed=NO

1. ActionableScore

* Raw base score: 2.
* Conservative score: 4. Real-UAF floor 4 applied: 2 -> 4.
* Raw paranoid score: 2.
* Paranoid score: 4. The same floor applies; no additional exploit primitive is supported.
* Final recommended bucket: **Borderline / manual review recommended**::

2. Signal breakdown

* +2 Real UAF: the receive worker can free the ACL parent after the request worker loads `conn->parent`, followed by a demonstrated one-byte read from freed `parent->features[0][3]`.
* +1 Reliable kernel crash/DoS: the slab UAF can plausibly produce an Oops or kernel crash.
* -1 Hard race: exploitation requires a narrow workqueue interleaving; the demonstrated KASAN result used an added 40 ms delay.
* Floor 4: this is an actual stale use of an active structured object, not fixed stale storage, and host-admin-only reachability is not proven.
* No structured stale-object leverage: the stale feature byte affects codec/parameter selection, but attacker-controlled reclaim, replacement contents, pointers, callbacks, or a later corrupting operation are not shown.
* No OOB write, repeated release, arbitrary write, disclosure, C/I impact, or additional availability effect is established.
* NEW52/B5-R does not apply: there is no retry-accumulated heap OOB write.
* B4-PENDING does not apply: no authorization decision is changed from DENY to ALLOW.

3. Reachability analysis

A local process must initiate SCO setup while ACL disconnection races the queued setup work; a Bluetooth peer may influence disconnection timing. The complete socket permission and capability requirements are not shown, so below-host-admin reachability, host UID 0 requirements, and namespace-scoped privilege remain unknown. A fully remote trigger is not established. No unusual hardware beyond an applicable Bluetooth setup is evidenced.

4. Primitive and severity reading

The primitive is a read-only slab UAF of an active ACL-parent object during normal SCO setup, not a cleanup-only dereference. The consumed stale byte selects enhanced-SCO parameters, but no post-free write, lifetime mutation, controlled reuse, or security-boundary crossing is shown. This is CLASS_B because the lifetime violation is concrete, while the demonstrated practical consequence is crash/DoS. Important-grade leverage is not materially evidenced, so automatic Moderate handling remains permissible after review.

5. One-sentence report phrase

A narrow Bluetooth workqueue race permits a demonstrated one-byte read from a freed ACL parent during SCO parameter selection, plausibly crashing the kernel without a shown write or reuse primitive.

6. Manual review advice

MANUAL CHECK RECOMMENDED

Confirm product-specific SCO socket permissions and whether an attacker can reliably drive both setup and disconnection without privileged assistance.

7. Call-site confidence

Call-site confidence: high

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

Patch: Bluetooth: hci_conn: Lock parent access during enhanced SCO setup
Commit: 1239ef0fa809b5952fca679db3faa3e1c00e1dac
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=1239ef0fa809b5952fca679db3faa3e1c00e1dac

Commit description:

Bluetooth: hci_conn: Lock parent access during enhanced SCO setup

hci_enhanced_setup_sync() runs on the request workqueue without the
hci_dev_lock held by its caller when setup was queued. Its CVSD
capability check and find_next_esco_param() dereference conn->parent
while the receive workqueue can unlink and release that parent.

The following interleaving can cause a use-after-free:

  hci_enhanced_setup_sync()       hci_disconn_complete_evt()
  load conn->parent
                                 hci_dev_lock()
                                 hci_conn_del(ACL parent)
                                   unlink SCO child
                                   drop link's parent reference
                                   clear child->parent
                                   release ACL parent
                                     bt_link_release()
                                       kfree(parent)
                                 hci_dev_unlock()
  read parent->features[0][3]

The reference held for the queued SCO child does not keep its ACL parent
alive after unlinking. Commit 42de40a ("Bluetooth: hci_conn: fix the
SCO setup context lifetime") protects the child stored in the queued
context, but leaves these parent accesses unprotected.

With a 40 ms diagnostic delay after loading conn->parent, an instrumented
kernel based on fd179f8 , which already contains 42de40a ,
reported:

  BUG: KASAN: slab-use-after-free in hci_enhanced_setup_sync+0xda5/0xdf0
  Read of size 1 at addr ffff888102204047 by task kworker/u17:0/93
  Call Trace:
   hci_enhanced_setup_sync+0xda5/0xdf0
   hci_cmd_sync_work+0x13c/0x290
   process_one_work+0x6b4/0x10e0

  Allocated by task 92:
   __hci_conn_add+0x304/0x1df0
   hci_connect_acl+0x349/0x3e0
   hci_connect_sco+0x3b/0x9a0
   sco_sock_connect+0x475/0xca0

  Freed by task 94:
   kfree+0x121/0x3c0
   bt_link_release+0x79/0xa0
   device_release+0xc8/0x240
   kobject_put+0x14d/0x280
   hci_conn_del+0x524/0xe30
   hci_disconn_complete_evt+0x403/0x8c0
   hci_event_packet+0x71b/0xb20
   hci_rx_work+0x293/0x730

The accessed address is 71 bytes into the freed ACL parent, at its
features[0][3] byte; the queued SCO child is a different object. The
diagnostic preserves the loaded parent across the delay, matching the
unmodified compiled capability check, and does not change the parent
references or teardown path.

Hold hci_dev_lock() across the codec switch, including every call to
find_next_esco_param(), and release it on all selection errors. Keep
configure_datapath_sync() outside the critical section because it waits
for HCI events. Preserve parameter selection and existing return values.

Fixes: e07a06b ("Bluetooth: Convert SCO configure_datapath to hci_sync")
Cc: stable@vger.kernel.org
Assisted-by: GPT-6-Astra
Signed-off-by: Chengfeng Ye <nicoyip.dev@gmail.com>
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/hci_conn.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=1239ef0fa809b5952fca679db3faa3e1c00e1dac

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

The original Linux kernel CVE announcement for CVE-2026-98736 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98736

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:N/I:N/A:H
  The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:H
  The Best / paranoid CVSS score: 5.8

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: 4

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).