[CVE-2026-64539][MODERATE 7.0] Bluetooth: eir: Fix stack OOB write when prepending the Flags AD [ Upstream

[CVE-2026-64539][MODERATE 7.0] Bluetooth: eir: Fix stack OOB write when prepending the Flags AD [ Upstream

[AL-KERNEL]

CVE: CVE-2026-64539
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: Bluetooth: eir: Fix stack OOB write when prepending the Flags AD [ Upstream
Commit: 0f0b6232af56441d0a2dcb173cc4f8d8aab39014
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=0f0b6232af56441d0a2dcb173cc4f8d8aab39014
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64539
Analysis date: Wed, 29 Jul 2026 01:35:04 -0400
ActionableScore: 7
ActionableScore lower bound: 4
Actionable bucket: Strong Important candidate / Actionable Moderate at minimum
Manual review required: YES

Summary:
A local CAP_NET_ADMIN attacker with access to an LE-only Bluetooth controller can trigger a stack OOB write in legacy advertising data construction, causing at least kernel DoS and requiring manual review for possible privilege escalation.

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

The original Linux kernel CVE announcement for CVE-2026-64539 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64539

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-2026-64539	MODERATE	CHECK WITH IMPACT FROM ORIG NN IMPORTANT	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H';*CWE-787;CWE-121;*CWE-20;Other CVSS 'AV:L/AC:L/PR:H/UI:N/S:U/C:L/I:L/A:H';BEST CVSS score: '7.8';DESCR 'eir_create_adv_data() can prepend a 3 byte Flags AD structure to a fixed size legacy advertising buffer and then copy user supplied instance advertising data without accounting for the added bytes. A local attacker who can configure Bluetooth advertising through CAP_NET_ADMIN on an LE-only controller can trigger a stack OOB write when adv_data_len already fills the legacy buffer. For the CVSS the PR:L is used in the paranoid score because CAP_NET_ADMIN may be delegated to a local service or container like context and is not always equivalent to full system administrator control in practical risk analysis. The issue is not network reachable over Bluetooth radio traffic because the malformed advertising instance must be configured locally through the management path. Impact is at least local denial of service via kernel crash and in worst case may allow confidentiality and integrity impact because this is a kernel stack OOB write with attacker influenced data.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 6) 	MAYBE	REMOTE WRITE KASAN OOB NETWORK KPANIC  KPANIC DECREASED_TO_MODERATE70_BASED_ON_ACTIONABLESCORELOWERTHAN7	-	-	checked

======================================================================
ACTIONABLESCORE ANALYSIS
======================================================================

ActionableScore=7
ActionableScoreLower=4

## 1. ActionableScore

* Conservative score: 4
* Paranoid score: 7
* Final recommended bucket: **Strong Important candidate / Actionable Moderate at minimum**::

## 2. Signal breakdown

Conservative signals:

* Generic memory corruption: +2. The patch fixes a confirmed stack OOB write in `eir_create_adv_data()`.
* Reliable kernel crash / strong DoS: +1. KASAN shows `stack-out-of-bounds` in a kernel workqueue path.
* Privileged kernel/device-management memory corruption path: +1. The bug is in Bluetooth controller advertising management code.
* Availability impact realistic: +1. A kernel stack overwrite can plausibly crash the host kernel.
* Requires CAP_NET_ADMIN in typical deployments: -2. The commit states the trigger requires a local user with `CAP_NET_ADMIN`.
* Corruption primitive constrained: -1. The overflow is small, around the prepended 3 byte Flags AD accounting gap, and the overwrite target is not freely selectable.

Conservative total: 4

Paranoid additional interpretation:

* Privilege escalation plausible: +2. The bug is a kernel stack OOB write with attacker-influenced advertising data, so LPE cannot be dismissed without manual analysis.
* Confidentiality impact plausible: +1. Stack corruption may theoretically affect kernel control/data flow.
* Integrity impact plausible: +1. Same reason, this is not just a NULL dereference or resource leak.
* Reduced CAP penalty: -1 instead of -2. `CAP_NET_ADMIN` may be delegated to a service, namespace-like environment, or constrained process and is not always equivalent to full host root in practical risk triage.

Paranoid total: 7

## 3. Reachability analysis

The bug is locally reachable through Bluetooth management operations that configure advertising instances. The described trigger requires an LE-only controller and the legacy advertising path. It is not remotely reachable over Bluetooth radio traffic because the malformed advertising data must be configured locally through the kernel management interface.

In typical deployments, this requires `CAP_NET_ADMIN`, so ordinary local users cannot trigger it directly. However, systems may delegate Bluetooth or network administration privileges to service accounts, desktop components, containers, or constrained management daemons. In those cases, the practical privilege requirement can be lower than full host-root control.

Call-site confidence: high. The commit includes the failing call chain through `hci_update_adv_data_sync()` and `hci_schedule_adv_instance_sync()`.

## 4. Severity interpretation

This is not an ordinary Moderate resource bug. It is confirmed kernel stack memory corruption with attacker-influenced data, but the trigger is local and capability-gated. Realistic impact may be kernel crash only, especially given the small overflow and lack of demonstrated target control. The paranoid interpretation treats it as an Important candidate because stack OOB writes have historically been under-triaged when exploitability was not immediately obvious.

## 5. One-sentence report phrase

A local CAP_NET_ADMIN attacker with access to an LE-only Bluetooth controller can trigger a stack OOB write in legacy advertising data construction, causing at least kernel DoS and requiring manual review for possible privilege escalation.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

Reason: this is a confirmed kernel stack OOB write, not just a warning or validation cleanup, and the overwrite contains attacker-influenced advertising data even though the trigger is capability-gated and hardware/path dependent.

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

Patch: Bluetooth: eir: Fix stack OOB write when prepending the Flags AD [ Upstream
Commit: 0f0b6232af56441d0a2dcb173cc4f8d8aab39014
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=0f0b6232af56441d0a2dcb173cc4f8d8aab39014

Changed files:
  net/bluetooth/eir.c
  mm/kasan/shadow.c
  net/bluetooth/hci_sync.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=0f0b6232af56441d0a2dcb173cc4f8d8aab39014

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

The original Linux kernel CVE announcement for CVE-2026-64539 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64539

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:L/PR:H/UI:N/S:U/C:L/I:L/A:H
  The Best / paranoid CVSS vector: AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
  The Best / paranoid CVSS score: 7.8

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: 4
  Paranoid ActionableScore: 7

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).