[CVE-2026-46138][MODERATE REGULAR] Bluetooth: hci_event: Fix OOB read and infinite loop in hci_le_create_big_complete_evt

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

CVE: CVE-2026-46138
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: Bluetooth: hci_event: Fix OOB read and infinite loop in hci_le_create_big_complete_evt
Commit: 6cb7f67bc28da787499291a562d49a084d9c90cd
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=6cb7f67bc28da787499291a562d49a084d9c90cd
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-46138
Analysis date: Thu, 28 May 2026 13:05:17 -0400
ActionableScore: 4
ActionableScore lower bound: 3
Actionable bucket: Borderline, manual review recommended
Manual review required: YES

Summary:
A malformed Bluetooth LE Create BIG Complete controller event can cause an OOB read from `bis_handle[]` and leave a BIG connection in `BT_BOUND` state, leading to an infinite loop with `hci_dev_lock` held and a realistic DoS.

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ABOUT THIS REPORT
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The original Linux kernel CVE announcement for CVE-2026-46138 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-46138

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 REGULAR
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-2026-46138	MODERATE	CHECK	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:A/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H';CWE-125;*CWE-835;*CWE-20;Other CVSS 'AV:P/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '5.3';DESCR 'A malformed LE Create BIG Complete event can make the Bluetooth HCI event handler read past the valid bis_handle flex array when fewer BIS handles are present than bound BIG connections. The out-of-bounds value is then used as an HCI handle and may be rejected, leaving the connection in BT_BOUND state and causing the same connection to be found again in a loop while hci_dev_lock is held. For the CVSS the PR:N is used because a malicious or faulty controller response does not require privileges on the victim once the affected controller path is reachable. The issue is firmware or controller mediated and is not clearly a normal remote Bluetooth packet parsing bug. Impact is mainly denial of service through a stuck HCI event path or kernel lockup, with no demonstrated information disclosure or privilege escalation primitive.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline, manual review recommended (with actual score 4) 	MAYBE	REMOTE WRITE OOB DANGER ERRORPATH NETWORK  LOWERED_FROM_HIGH_BASED_ON_GUESSCVSS  DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5	-	-	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=4
ActionableScoreLower=3

## 1. ActionableScore

* Conservative score: **3**
* Paranoid score: **4**
* Final recommended bucket: **Borderline, manual review recommended**::

## 2. Signal breakdown

* Firmware-mediated external influence: **+1**. The malformed `LE_Create_BIG_Complete` event is supplied by the Bluetooth controller.
* Reliable kernel crash / strong DoS: **+1**. The OOB value can keep the connection in `BT_BOUND` state and create an infinite loop while `hci_dev_lock` is held.
* Availability impact realistic: **+1**. A stuck HCI event handler can hang Bluetooth processing and may affect system responsiveness.
* Broad subsystem exposure, paranoid only: **+1**. Bluetooth is common, and this is in the HCI event path, although the specific BIG/BIS ISO path is more specialized.
* Weak read-only OOB: **+0**. The primitive is an OOB read from a flex array, not an OOB write, UAF, double-free, or controlled overwrite.
* No confidentiality signal: **+0**. The OOB bytes are used as an internal HCI handle and are not shown to be disclosed to userspace or a peer.
* No integrity / LPE signal: **+0**. No write primitive or realistic privilege escalation path is shown.
* Specific controller / feature condition: **0 to -1 considered**. The path requires affected Bluetooth controller behavior and BIG/BIS setup, but I do not apply a strong rare-hardware penalty because it is still in the main Bluetooth stack.

## 3. Reachability analysis

The direct trigger is a malformed Bluetooth controller event, not a normal userspace syscall and not clearly an over-the-air Bluetooth packet parser. A malicious or faulty controller can trigger it without local privileges on the host once the affected controller path is active. A remote Bluetooth-adjacent attacker is only a paranoid possibility if they can cause the controller to emit the malformed BIG completion event, but that is not demonstrated by the patch. Namespaces and containers do not materially lower the trigger requirement because the critical input comes from the controller event stream.

## 4. Severity interpretation

This behaves like a **borderline actionable Moderate** issue. The realistic impact is DoS through an infinite loop with `hci_dev_lock` held. The theoretical OOB read is real, but it is read-only and not shown to leak data or corrupt memory. There is no supported LPE primitive, so it should not be treated as Important without additional evidence of remote controller manipulation or disclosure.

## 5. One-sentence report phrase

A malformed Bluetooth LE Create BIG Complete controller event can cause an OOB read from `bis_handle[]` and leave a BIG connection in `BT_BOUND` state, leading to an infinite loop with `hci_dev_lock` held and a realistic DoS.

## 6. Manual review recommendation

**MANUAL CHECK RECOMMENDED**

Manual review is recommended because this is a core Bluetooth HCI event path with controller-supplied malformed input and a lock-held infinite loop, but the current evidence supports DoS only and not information disclosure or privilege escalation.

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UPSTREAM PATCH SUMMARY
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Patch: Bluetooth: hci_event: Fix OOB read and infinite loop in hci_le_create_big_complete_evt
Commit: 6cb7f67bc28da787499291a562d49a084d9c90cd
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=6cb7f67bc28da787499291a562d49a084d9c90cd

Commit description:

hci_le_create_big_complete_evt() iterates over BT_BOUND connections for
a BIG handle using a while loop, accessing ev->bis_handle[i++] on each
iteration.  However, there is no check that i stays within ev->num_bis
before the array access.

When a controller sends a LE_Create_BIG_Complete event with fewer
bis_handle entries than there are BT_BOUND connections for that BIG,
or with num_bis=0, the loop reads beyond the valid bis_handle[] flex
array into adjacent heap memory.  Since the out-of-bounds values
typically exceed HCI_CONN_HANDLE_MAX (0x0EFF), hci_conn_set_handle()
rejects them and the connection remains in BT_BOUND state.  The same
connection is then found again by hci_conn_hash_lookup_big_state(),
creating an infinite loop with hci_dev_lock held.

Fix this by terminating the BIG if in case not all BIS could be setup
properly.

Fixes: a0bfde1 ("Bluetooth: ISO: Add support for connecting multiple BISes")
Cc: stable@vger.kernel.org
Signed-off-by: ZhiTao Ou <hkbinbinbin@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_event.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=6cb7f67bc28da787499291a562d49a084d9c90cd

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

The original Linux kernel CVE announcement for CVE-2026-46138 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-46138

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:P/AC:L/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:N/I:N/A:H
  The Best / paranoid CVSS score: 5.3

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: 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: NO
Published priority for this report (same as in Subject): MODERATE REGULAR

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).