* [CVE-2026-97975][MODERATE 7.0] Bluetooth: hci_sysfs: Fix NULL pointer dereference in device_del() [ Upstream
@ 2026-09-25 11:35 21% AL-KERNEL
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From: AL-KERNEL @ 2026-09-25 11:35 UTC (permalink / raw)
To: kernel-cve
CVE: CVE-2026-97975
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: Bluetooth: hci_sysfs: Fix NULL pointer dereference in device_del() [ Upstream
Commit: eeabdb25c3209569367e99a85ca9a503b64a646d
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=eeabdb25c3209569367e99a85ca9a503b64a646d
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-97975
Analysis date: Fri, 25 Sep 2026 07:35:59 -0400
ActionableScore: 4
ActionableScore lower bound: unknown
Actionable bucket: Borderline / manual review recommended
Manual review required: YES
Summary:
No one-sentence report phrase was found.
======================================================================
ABOUT THIS REPORT
======================================================================
The original Linux kernel CVE announcement for CVE-2026-97975 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-97975
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-2026-97975 MODERATE https://www.kernelcve.org/list/?q=CVE-2026-97975 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:L/I:L/A:H';CWE-362;*CWE-416;**CWE-476;Other CVSS 'AV:A/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '6.4';DESCR 'A race in Bluetooth hci_conn_del_sysfs can occur when a child device is being unregistered while the connection cleanup path reparents child devices. A BNEP network device can be removed from its parent klist by device_move while device_del still uses a stale parent state, resulting in a NULL pointer dereference in klist_put and a kernel crash. The missing explicit reference from the connection device to the HCI parent device also creates a stale device lifetime reference and an underlying use after free candidate. For the CVSS the PR:N is used because a nearby Bluetooth peer may trigger the affected BNEP connection and teardown activity without local code execution on the target. The attack vector is adjacent because Bluetooth communication requires radio proximity. The race requires timing control and therefore AC:H. Impact is at least denial of service via kernel crash and in the worst case may allow limited confidentiality or integrity impact due to the device lifetime use after free condition. This issue should be reviewed manually.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline / manual review recommended (with actual score 4) YES REMOTE DANGER NULLPTR RACE UAF NETWORK HARDWARE SYZBOT KPANIC YES NO checked
======================================================================
ACTIONABLESCORE ANALYSIS
======================================================================
ActionableScore=4
PrimitiveClass=CLASS_B
RealUAF=YES
HostAdminRequired=UNKNOWN
NamespaceScopedPrivilege=UNKNOWN
ImportantCandidate=NO
ManualReview=RECOMMENDED
AutoDowngradeAllowed=YES
1. ActionableScore
* Raw conservative score: 3
* Conservative score: 4
* Raw paranoid score: 3
* Paranoid score: 4
* Applied conservative floor: Real UAF floor 4 changed 3 to 4.
* Applied paranoid floor: Real UAF floor 4 changed 3 to 4.
* Final recommended bucket: **Borderline / manual review recommended**::
2. Signal breakdown
* +2 Real UAF or lifetime violation. `conn->dev.parent` previously did not hold a device reference to `hdev->dev`. The parent device could therefore be released while `conn->dev` still retained and later used its stale parent pointer. The added `get_device()` at initialization and `put_device()` at connection-device release directly establish the intended parent lifetime invariant.
* +1 Reliable kernel crash or strong DoS. The reported race has a concrete NULL pointer dereference in `klist_put()` during `device_del()`. This can produce an Oops or kernel crash.
* No direct network reachability +2. Bluetooth and BNEP are involved, but the supplied patch does not establish that a nearby unauthenticated Bluetooth peer can complete the full trigger without preexisting local BNEP or PAN provisioning and connection setup.
* No local unprivileged trigger +1. The complete privilege and service setup requirements for creating the relevant BNEP child device and driving both teardown paths are not established.
* No hard-race penalty. The bug is a race, but the supplied evidence does not prove that its timing is unusually narrow, externally uncontrollable, or effectively one-shot.
* No structured stale-object leverage +1. The stale parent use is in connection-device release and cleanup processing. There is no demonstrated controlled reclaim, attacker-controlled replacement object, callback dispatch, attacker-shaped post-free field consumption, arbitrary read, or arbitrary write.
* No concrete repeated release or refcount mutation +1. The pre-fix code lacks a required parent reference. It does not show an earlier `put_device(parent)` followed by a second `put_device(parent)` through the same exact dangling reference. The stale `put_device()` is a single potentially post-lifetime use, not a demonstrated double put sequence.
* No Confidentiality or Integrity points. The patch establishes a stale-lifetime condition and crash path, but does not establish information disclosure, unauthorized modification, controlled reallocation, or a security-boundary bypass.
* No paranoid-only bonus. The patch-supported mechanics do not establish a distinct post-free refcount takeover, controlled reuse, or other stronger primitive beyond the concrete UAF and crash path.
3. Reachability analysis
The directly demonstrated trigger is a concurrent lifecycle race between `hci_conn_del_sysfs()` and child device unregistration. The concrete example is a BNEP network device being removed through `unregister_netdev()` while the Bluetooth connection cleanup path attempts to move child devices.
A nearby Bluetooth peer may influence connection establishment and teardown in a deployment using Bluetooth PAN or BNEP. However, the supplied code does not establish that the same peer can create the BNEP child device, cause its unregister operation, and reliably trigger the concurrent `hci_conn_del_sysfs()` path without a locally configured Bluetooth PAN service or local management activity.
Host-admin-equivalent privilege is not positively established, but below-host-admin reachability for the complete sequence is also not proven. Therefore `HostAdminRequired=UNKNOWN`.
No evidence shows that all required operations can be completed through attacker-controlled user or network namespaces. Therefore `NamespaceScopedPrivilege=UNKNOWN`.
No unusual physical hardware is required beyond an available Bluetooth adapter. No host boot option or sysctl prerequisite is established by the patch. BNEP or PAN configuration may be a practical deployment prerequisite, but this is not used as a negative score penalty because the supplied evidence does not fully resolve that setup boundary.
4. Primitive and severity interpretation
The primary observed primitive is a race-driven invalid device-list state. `device_del()` retains a snapshot of a non-NULL parent relationship while concurrent `device_move()` removes the same child from the parent klist and clears its parent-klist linkage. The later `klist_del()` reaches `klist_put()` with an already-invalid node state and dereferences NULL.
The patch also establishes a real parent-device lifetime violation. Before the fix, `conn->dev.parent` pointed to `hdev->dev` without an explicit retained device reference. A connection device could outlive the HCI parent device and later release or otherwise use a stale parent pointer. This is a real UAF or stale post-lifetime object-use candidate, not merely a bookkeeping issue.
The stale object is an active `struct device`, but the visible stale operation is constrained to cleanup and release behavior. There is no demonstrated attacker-controlled object replacement, post-free structured field consumption, callback use, refcount takeover, arbitrary write, disclosure, or privilege escalation path. The patch does not establish a concrete repeated release or refcount mutation on the exact same dangling reference.
This is therefore `CLASS_B`, not `CLASS_A`. The confirmed operational consequence is kernel DoS through NULL dereference or stale-device lifetime misuse. Privilege escalation remains speculative and is not used for scoring. The issue warrants manual review because it contains a real device-lifetime UAF condition, but the supplied evidence supports a constrained cleanup-path UAF rather than an Important-grade exploitation primitive.
`ImportantCandidate=NO` because meaningful exploitation leverage beyond cleanup-path crash behavior is not established. `AutoDowngradeAllowed=YES` because there is no demonstrated controlled reclaim, repeated stale lifetime mutation, security-boundary bypass, or unresolved active-object reuse primitive requiring Important-vs-Moderate preservation.
5. One-sentence report phrase
A race between Bluetooth child-device reparenting and BNEP device unregistration can cause a NULL pointer dereference and exposes a stale HCI parent-device lifetime reference, leading to kernel denial of service.
6. Manual review recommendation
MANUAL CHECK RECOMMENDED
A real parent-device lifetime violation is fixed, but the visible stale uses are cleanup-related and no controlled reuse, write primitive, or privilege-escalation mechanism is established.
7. Call-site confidence
Call-site confidence: medium
======================================================================
UPSTREAM PATCH SUMMARY
======================================================================
Patch: Bluetooth: hci_sysfs: Fix NULL pointer dereference in device_del() [ Upstream
Commit: eeabdb25c3209569367e99a85ca9a503b64a646d
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=eeabdb25c3209569367e99a85ca9a503b64a646d
Changed files:
net/bluetooth/hci_sysfs.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=eeabdb25c3209569367e99a85ca9a503b64a646d
======================================================================
DETAILED REPORT METHODOLOGY
======================================================================
The original Linux kernel CVE announcement for CVE-2026-97975 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-97975
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:H/PR:N/UI:N/S:U/C:L/I:L/A:H
The Best / paranoid CVSS score: 6.4
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 [email protected] (and both
send reply to CVE record itself too and see "reply" button below for howto reply).
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