[CVE-2026-53073][MODERATE 7.0] Bluetooth: hci_ldisc: Clear HCI_UART_PROTO_INIT on error [ Upstream

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

CVE: CVE-2026-53073
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: Bluetooth: hci_ldisc: Clear HCI_UART_PROTO_INIT on error [ Upstream
Commit: ebb39b2d81731b83ee71a1ba6dd0291a57b5ac07
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=ebb39b2d81731b83ee71a1ba6dd0291a57b5ac07
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53073
Analysis date: Thu, 25 Jun 2026 05:04:46 -0400
ActionableScore: 6
ActionableScore lower bound: 3
Actionable bucket: Strong Important candidate / Actionable Moderate at minimum
Manual review required: YES

Summary:
A race in Bluetooth HCI UART error handling can leave `HCI_UART_PROTO_INIT` set after registration failure, allowing incoming UART data to reach protocol receive handlers after resources are freed and potentially causing a kernel crash or UAF-based impact.

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

The original Linux kernel CVE announcement for CVE-2026-53073 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53073

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-2026-53073	MODERATE	CHECK	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-476;CWE-667;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '7';DESCR 'A race in Bluetooth hci_ldisc can leave HCI_UART_PROTO_INIT set after hci_register_dev fails, allowing incoming UART data to enter the protocol receive handler after protocol resources have been closed or freed. This can result in a NULL pointer dereference or a use after free in the kernel receive path and can crash the system. For the CVSS the PR:L is used for the paranoid score because a local user or service account with access to the HCI UART setup path or relevant tty may be able to trigger the failing registration and race in some deployments. The issue is not directly network reachable over IP and is tied to local or physically attached UART based Bluetooth controller handling. Impact is at least local denial of service via kernel crash. Because the receive path may run after freed resources are reachable, the worst case is treated as possible confidentiality and integrity impact for manual review.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 5) 	MAYBE	NULLPTR INIT SIMPLEFIX RACE HARDWARE KPANIC 	-	-	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=6
ActionableScoreLower=3

## 1. ActionableScore

* Conservative score: **3**
* Paranoid score: **6**
* Final recommended bucket: **Strong Important candidate / Actionable Moderate at minimum**::

## 2. Signal breakdown

Paranoid score signals:

* **Generic memory corruption: +2**
  The commit states that incoming UART data can reach protocol-specific receive handlers after resources are freed. This is a UAF candidate, not just a warning-only bug.

* **Real lifetime corruption: +1**
  The bug is explicitly a lifetime/order issue: `HCI_UART_PROTO_INIT` remains set while `proto->close()` and `hci_free_dev()` tear down resources.

* **Reliable kernel crash / strong DoS: +1**
  The commit mentions risk of NULL pointer dereference, and the receive path after teardown can realistically crash the kernel.

* **Weak LPE concern: +1**
  A receive handler operating on freed protocol/HCI state gives a theoretical privilege-escalation concern, but the patch does not show a controlled reclaim or arbitrary write primitive.

* **Privileged kernel/device-management memory corruption path: +1**
  This is inside Bluetooth HCI UART device registration/teardown and protocol receive handling, a trusted kernel device-management path.

* **Hard or unreliable race / special timing required: -1**
  Triggering requires failure of `hci_register_dev()` plus incoming UART data during a teardown window.

Conservative score additionally applies stronger privilege/configuration caution:

* **Requires admin/root/CAP_NET_ADMIN in typical deployments: -2**
  Setting up HCI UART line discipline and Bluetooth HCI device registration is normally done by root or privileged services.

* **Rare or configuration-dependent path: -1**
  HCI UART Bluetooth controllers are less common than USB Bluetooth or core networking paths.

## 3. Reachability analysis

The bug is local or device-adjacent, not IP network reachable. A typical attacker would need local influence over HCI UART setup, a privileged Bluetooth initialization service, a delegated tty, or a misconfigured environment where a less-privileged account can interact with the relevant UART/line-discipline path. In normal deployments this is closer to PR:H, but in embedded, containerized, service-account, or delegated-device environments PR:L is defensible for paranoid triage.

The affected path is not universally default-enabled. It depends on Bluetooth HCI over UART and an error during device registration. Realistic exploitation requires timing or a controllable failure path, but the lifetime bug is credible because the patch uses a write lock to prevent receive-path readers from entering before freeing resources.

## 4. Severity interpretation

This is not an ordinary low-risk cleanup. It is a race/lifetime bug with possible UAF or NULL dereference in a kernel receive path. Realistic impact is most likely local DoS via kernel crash. Theoretical memory-corruption impact is plausible enough for manual review, but there is no demonstrated strong LPE primitive such as controlled reclaim, arbitrary write, or object replacement.

Overall this is **Actionable Moderate**, with **Strong Important candidate** treatment reasonable for paranoid triage because it is a kernel UAF candidate in a device receive path.

## 5. One-sentence report phrase

A race in Bluetooth HCI UART error handling can leave `HCI_UART_PROTO_INIT` set after registration failure, allowing incoming UART data to reach protocol receive handlers after resources are freed and potentially causing a kernel crash or UAF-based impact.

## 6. Manual review recommendation

**MANUAL CHECK REQUIRED**

Reason: the patch context supports a real lifetime bug and possible UAF in a kernel receive path. Even though practical triggering is likely local and configuration-dependent, it should not be auto-closed without reviewing reachable protocols, tty permissions, embedded deployments, and whether freed objects can be reclaimed or influenced.

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

Patch: Bluetooth: hci_ldisc: Clear HCI_UART_PROTO_INIT on error [ Upstream
Commit: ebb39b2d81731b83ee71a1ba6dd0291a57b5ac07
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=ebb39b2d81731b83ee71a1ba6dd0291a57b5ac07

Changed files:
  drivers/bluetooth/hci_ldisc.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=ebb39b2d81731b83ee71a1ba6dd0291a57b5ac07

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

The original Linux kernel CVE announcement for CVE-2026-53073 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53073

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:N/I:N/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: 3
  Paranoid ActionableScore: 6

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).