* [CVE-2026-97977][MODERATE 7.0] Bluetooth: btusb: Fix UAF of btusb_data by rx_work [ Upstream
@ 2026-09-30 6:03 21% AL-KERNEL
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From: AL-KERNEL @ 2026-09-30 6:03 UTC (permalink / raw)
To: kernel-cve
CVE: CVE-2026-97977
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: Bluetooth: btusb: Fix UAF of btusb_data by rx_work [ Upstream
Commit: 472d005622525b7be155cac99dde2252b0163bd1
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=472d005622525b7be155cac99dde2252b0163bd1
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-97977
Analysis date: Wed, 30 Sep 2026 02:03:07 -0400
ActionableScore: 5
ActionableScore lower bound: 4
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-2026-97977 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-97977
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-2026-97977 MODERATE https://www.kernelcve.org/list/?q=CVE-2026-97977 CHECK WITH IMPACT FROM ORIG NN LOW 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-416;CWE-362;CWE-667;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:L/I:L/A:H';BEST CVSS score: '7';DESCR 'A race in the Bluetooth btusb teardown path allows rx_work to continue running after btusb_data has been freed because cancel_delayed_work does not wait for work that is already executing on another CPU. The remaining worker can dereference the freed ACL queue, HCI device pointer, and recv_acl callback after USB device disconnect. An URB completion can also requeue rx_work if traffic is not stopped before synchronous cancellation. Impact is at least a local denial of service through a kernel crash. Because this is a confirmed use after free involving an indirect callback stored in the freed object, controlled memory reuse may potentially result in confidentiality loss, integrity impact, or privilege escalation and requires manual review. For the CVSS the PR:L value is used for the paranoid score because Bluetooth or device management may be delegated to a restricted service, container, or user with limited capabilities rather than full host administration. AC:H reflects the requirement to win a timing dependent race between delayed work execution and device teardown. The issue is not directly network reachable by a remote Bluetooth peer alone because freeing btusb_data also requires local, administrative, or physical device disconnection.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate / Strong Important candidate requiring manual review (with actual score 5) MAYBE USB INIT UAF SKB HARDWARE KPANIC KPANIC INCREASED_TO_HIGH_BASED_ON_GUESSCVSS DECREASED_TO_MODERATE7_BASED_ON_FALSEPOSCHECKOFDH - - checked
======================================================================
ACTIONABLESCORE ANALYSIS
======================================================================
ActionableScore=5
ActionableScoreLower=4
PrimitiveClass=CLASS_B
RealUAF=YES
HostAdminRequired=UNKNOWN
NamespaceScopedPrivilege=NO
ImportantCandidate=YES
ManualReview=REQUIRED
AutoDowngradeAllowed=NO
1. ActionableScore
* Raw conservative score: 3
* Conservative score: 4
* Raw paranoid score: 3
* Paranoid score: 5
* Applied conservative floor: 3 -> 4 because a real post-lifetime dereference reaches multiple fields of an active structured object rather than only a fixed transfer buffer.
* Applied paranoid floor: 3 -> 5 because the stale worker performs queue processing and an indirect call through `data->recv_acl`, leaving meaningful exploitation leverage unresolved despite no demonstrated controlled reclaim.
* Final recommended bucket: **Actionable Moderate / Strong Important candidate requiring manual review**::
2. Signal breakdown
Positive signals:
* +2 Real UAF. `btusb_data` is freed after `hci_unregister_dev()` while an asynchronously running `btusb_rx_work()` can retain and dereference the same object.
* +1 Reliable kernel crash or strong DoS. Access to the freed ACL queue, HCI pointer, or callback can produce a kernel fault.
Negative signals:
* No negative privilege score. Host-admin-equivalent privilege is not established as mandatory because physical USB removal is another possible teardown source.
* No race penalty. The patch establishes a race, but does not establish that it is sufficiently narrow, uncontrollable, or unreliable to justify minus one.
* No rare-hardware penalty. A USB Bluetooth adapter is required, but the supplied evidence does not establish rare or unusual hardware.
Important non-awarded signals:
* Controlled reclaim or attacker-shaped replacement contents are not demonstrated.
* Arbitrary or directed kernel read/write is not demonstrated.
* Strong exploitation leverage +2 is not awarded merely because a stale callback is invoked.
* Structured stale-object leverage +1 is withheld because the supplied evidence does not show meaningful attacker control over reclaimed contents or object replacement.
* Local unprivileged trigger +1 is not awarded because an ordinary user is not shown to control the complete traffic plus device-disconnect sequence.
* Remote reachability +2 is not awarded because a Bluetooth peer alone is not shown to free `btusb_data`.
* No additional Availability point is awarded because it would duplicate the same kernel-crash consequence.
* Confidentiality and Integrity points are not awarded. Post-free callback dispatch creates unresolved concern, but no disclosure, protected-state modification, or successful callback hijack is established.
* No concrete repeated release or refcount mutation exists. The stale worker dereferences and processes the freed object but does not perform a second `put`, `free`, or refcount decrement on the exact reference.
* The repeated-release paranoid bonus and repeated-release FLOOR 5 condition do not apply.
3. Reachability analysis
The complete trigger requires `rx_work` to be executing or requeued while the USB Bluetooth device is being closed and disconnected. A host administrator can likely initiate driver unbind or equivalent device teardown, and a physical actor can disconnect a USB adapter, but the supplied evidence does not establish one mandatory attacker model. Therefore `HostAdminRequired=UNKNOWN`.
An ordinary local user is not shown to control the complete teardown operation. A remote Bluetooth peer may influence receive activity and help keep `rx_work` active, but it is not shown to trigger the required USB disconnect independently. The complete operation is host-device-global rather than confined to an attacker-created namespace, so `NamespaceScopedPrivilege=NO`.
A USB Bluetooth adapter and the affected queued polling path are prerequisites. They are hardware and feature dependencies, but not enough to justify a rare-hardware penalty. The race can potentially be retried through device reconnection and renewed traffic, but reliable attacker control over those stages is not established.
4. Primitive and severity interpretation
The exact primitive is an asynchronous post-teardown UAF. `cancel_delayed_work()` can return while `btusb_rx_work()` is running, after which `btusb_disconnect()` frees `btusb_data`. The stale worker then accesses `data->acl_q`, `data->hdev`, and `data->recv_acl`.
This is an active structured object rather than a simple fixed data buffer. The stale path performs queue traversal and an indirect callback invocation. It is broader than an immediate poisoned-pointer fault, although the supplied evidence does not demonstrate attacker-controlled replacement of the freed allocation.
There is no concrete second lifetime or refcount mutation. This is category A, an ordinary stale post-lifetime dereference and structured callback use, rather than category B, a second `put`, `free`, or refcount mutation through the dangling reference.
The demonstrated consequence is kernel crash and denial of service. Callback hijacking, kernel code execution, and privilege escalation remain speculative because controlled reclaim and callback contents are not established.
`PrimitiveClass=CLASS_B` is appropriate because the actual UAF and post-free structured processing are concrete, but no Class A exploitation primitive is demonstrated. `ImportantCandidate=YES` reflects the unresolved post-free indirect callback path, not a claim that exploitation is proven. `AutoDowngradeAllowed=NO` because automatically treating this as an ordinary crash-only driver issue would discard a concrete active-object UAF whose stale path invokes a callback.
Likely operational severity is Actionable Moderate pending manual analysis of allocator reuse, attacker influence over Bluetooth receive traffic, device teardown permissions, and whether reclaimed `btusb_data` contents can affect the indirect call.
5. One-sentence report phrase
A teardown race allows btusb rx_work to process a freed btusb_data object and invoke its stale receive callback, causing at least a kernel crash while leaving post-reclaim callback exploitation unresolved.
6. Manual review recommendation
MANUAL CHECK REQUIRED
The confirmed UAF reaches an indirect callback after object destruction, so reclaim feasibility and callback influence should be examined before assigning an ordinary Moderate disposition.
7. Call-site confidence
Call-site confidence: high
======================================================================
UPSTREAM PATCH SUMMARY
======================================================================
Patch: Bluetooth: btusb: Fix UAF of btusb_data by rx_work [ Upstream
Commit: 472d005622525b7be155cac99dde2252b0163bd1
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=472d005622525b7be155cac99dde2252b0163bd1
Changed files:
drivers/bluetooth/btusb.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=472d005622525b7be155cac99dde2252b0163bd1
======================================================================
DETAILED REPORT METHODOLOGY
======================================================================
The original Linux kernel CVE announcement for CVE-2026-97977 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-97977
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:H/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: 4
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 [email protected] (and both
send reply to CVE record itself too and see "reply" button below for howto reply).
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