[CVE-2026-68339][MODERATE REGULAR] Bluetooth: btusb: validate Realtek vendor event length [ Upstream

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

CVE: CVE-2026-68339
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: Bluetooth: btusb: validate Realtek vendor event length [ Upstream
Commit: 8de58bfa26e028f99271dde5a92107cd07f5e063
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=8de58bfa26e028f99271dde5a92107cd07f5e063
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-68339
Analysis date: Mon, 10 Aug 2026 15:56:24 -0400
ActionableScore: 2
ActionableScore lower bound: 1
Actionable bucket: Ordinary Moderate / Low-like
Manual review required: NO

Summary:
A short Realtek Bluetooth vendor event can cause `btusb_recv_event_realtek()` to read `skb->data[2]` before validating that the byte exists, resulting in a limited kernel out-of-bounds read and possible coredump misclassification, but no supported privilege escalation or remote network attack path is shown.

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ABOUT THIS REPORT
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The original Linux kernel CVE announcement for CVE-2026-68339 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-68339

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: NO

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-2026-68339	MODERATE	CHECK WITH IMPACT FROM ORIG NN LOW	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:P/AC:L/PR:N/UI:R/S:U/C:L/I:N/A:L';CWE-125;*CWE-20;CWE-754;Other CVSS 'AV:P/AC:H/PR:N/UI:R/S:U/C:N/I:N/A:L';BEST CVSS score: '3.2';DESCR 'A short Realtek Bluetooth vendor event can reach btusb_recv_event_realtek with less than three bytes of event data, while the old classifier reads data byte 2 before validating that the Realtek subevent byte is present. This is a small out of bounds read in the local btusb receive path and may misclassify a malformed event as a Realtek coredump if the adjacent byte has the expected value. For the CVSS the PR:N is used because the attacker does not need an account on the victim once a malicious or compromised Bluetooth USB controller is the input source. The issue is not directly network reachable over Bluetooth packet traffic and normally requires physical device control or compromised local controller firmware. Impact is mainly denial of service or diagnostic misbehavior. In the paranoid score confidentiality is limited because an out of bounds read exists, but there is no supported arbitrary write, UAF, or privilege escalation primitive.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate / Low-like (with actual score 2)	YES	USB SIMPLEFIX SKB DEBUGFS  INCREASED_FROM_LOW_BASED_ON_REQUIREMANUALCHECK DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5	YES	NO	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=2
ActionableScoreLower=1

## 1. ActionableScore

* Conservative score: 1
* Paranoid score: 2
* Final recommended bucket: **Ordinary Moderate / Low-like**

## 2. Signal breakdown

Conservative signals:

* Firmware-mediated external influence: +1. The malformed input is an HCI event delivered by a local Realtek USB Bluetooth controller or its firmware, not a normal remote network packet.
* No strong memory corruption primitive: +0. The bug is a one-byte out-of-bounds read from `skb->data[2]`, not an OOB write, UAF, double free, type confusion, or arbitrary write.
* No reliable kernel crash shown: +0. The commit describes misclassification as a coredump, not a demonstrated panic or persistent host-wide DoS.
* No LPE signal: +0. There is no reclaim, write primitive, callback control, refcount takeover, or attacker-controlled object replacement.
* Constrained read-only primitive: -1. The read is small and used only for classification.
* Physical or firmware control requirement: effectively limits exposure. I do not apply full remote reachability.

Paranoid additional signals:

* Confidentiality impact plausible: +1. Because an OOB read exists in kernel memory, a limited confidentiality concern is technically possible, but the patch does not show a user-visible leak path.
* Availability impact weakly plausible: +0 or +1 considered, but not counted separately because no reliable crash path is shown.

## 3. Reachability analysis

The realistic trigger is a malformed Realtek vendor HCI event received through the local `btusb` driver path. A normal remote Bluetooth peer does not directly control this USB HCI event stream in the same way as a network protocol parser. Practical exploitation would usually require a malicious USB Bluetooth device, compromised controller firmware, or a test setup able to inject malformed HCI events.

No local Linux user account is required once the malicious device or firmware is the input source, but the attack is not network-reachable in the usual AV:N sense. Namespaces and containers do not materially lower the requirement, because the vulnerable input originates from the physical or firmware-mediated Bluetooth controller path.

Call-site confidence: high for the immediate bug, because the patch directly shows the missing `skb->len` check before `skb->data[2]`. Confidence is lower for downstream impact because the full coredump handling path is not included.

## 4. Severity interpretation

This behaves like a low-end memory-safety validation bug, not an Important-class kernel vulnerability. The theoretical issue is an out-of-bounds read and possible coredump misclassification. Realistic exploitation evidence is weak because there is no demonstrated disclosure path, no write primitive, no UAF, no privilege escalation path, and no reliable kernel crash described.

The issue should not be treated as remote network-triggerable. It is best triaged as ordinary Moderate or Low-like, with manual review only because kernel OOB reads can sometimes hide secondary effects.

## 5. One-sentence report phrase

A short Realtek Bluetooth vendor event can cause `btusb_recv_event_realtek()` to read `skb->data[2]` before validating that the byte exists, resulting in a limited kernel out-of-bounds read and possible coredump misclassification, but no supported privilege escalation or remote network attack path is shown.

## 6. Manual review recommendation

MANUAL CHECK RECOMMENDED

Manual review is recommended because this is a kernel out-of-bounds read in a device input path, but the current evidence supports only low practical severity and does not justify Important-class handling.

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

Patch: Bluetooth: btusb: validate Realtek vendor event length [ Upstream
Commit: 8de58bfa26e028f99271dde5a92107cd07f5e063
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=8de58bfa26e028f99271dde5a92107cd07f5e063

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=8de58bfa26e028f99271dde5a92107cd07f5e063

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

The original Linux kernel CVE announcement for CVE-2026-68339 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-68339

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:H/PR:N/UI:R/S:U/C:N/I:N/A:L
  The Best / paranoid CVSS vector: AV:P/AC:L/PR:N/UI:R/S:U/C:L/I:N/A:L
  The Best / paranoid CVSS score: 3.2

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: 1
  Paranoid ActionableScore: 2

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).