[CVE-2026-74300][MODERATE REGULAR] Bluetooth: hci: validate codec capability element length [ Upstream

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

CVE: CVE-2026-74300
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: Bluetooth: hci: validate codec capability element length [ Upstream
Commit: fc97fc8cf7f53fd3619db63e09050d20a3a0c4b1
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=fc97fc8cf7f53fd3619db63e09050d20a3a0c4b1
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74300
Analysis date: Sun, 16 Aug 2026 07:51:07 -0400
ActionableScore: 4
ActionableScore lower bound: 2
Actionable bucket: Borderline Moderate, manual review recommended but not Strong Important
Manual review required: YES

Summary:
A truncated Bluetooth HCI Read Local Codec Capabilities response can cause hci_read_codec_capabilities() to copy one byte beyond the advertised response payload into the cached codec list, creating a limited OOB read and possible low-impact information disclosure if attacker influence over a controller or HCI injection path exists.

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ABOUT THIS REPORT
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The original Linux kernel CVE announcement for CVE-2026-74300 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74300

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-2026-74300	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:L/I:N/A:L';CWE-125;CWE-126;*CWE-20;Other CVSS 'AV:P/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N';BEST CVSS score: '4.4';DESCR 'A truncated Bluetooth HCI Read Local Codec Capabilities response can pass validation because hci_read_codec_capabilities checked only the payload length and did not include the one byte length field in the required element size. This can make the parser record a capability element that extends one byte beyond the advertised response payload and copy that extra byte into the cached codec capability list. For the CVSS the PR:L is used for the paranoid score because a local user or service with access to an HCI injection path or a virtual controller path may be able to provide the malformed controller response. In the typical hardware threat model the issue requires a malformed or malicious local Bluetooth controller rather than a remote Bluetooth peer. Impact is mainly limited information disclosure from a small out of bounds read, with possible low availability impact if malformed responses disrupt controller capability parsing.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline Moderate, manual review recommended but not Strong Important (with actual score 3)	YES	REMOTE SIMPLEFIX NETWORK SKB  LOWERED_FROM_HIGH_BASED_ON_GUESSCVSS  DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5	NO	NO	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=4
ActionableScoreLower=2

## 1. ActionableScore

* Conservative score: 2
* Paranoid score: 4
* Final recommended bucket: **Borderline Moderate, manual review recommended but not Strong Important**::

## 2. Signal breakdown

Conservative signals:

* Firmware-mediated external influence: +1
  The malformed input is a Bluetooth controller response, not ordinary remote Bluetooth peer traffic.
* Confidentiality impact plausible: +1
  The parser can copy one byte beyond the advertised response payload into the cached codec capability list, so a limited information disclosure path is plausible if that cached data is later exposed.

Paranoid additional signals:

* Local unprivileged or reduced-privilege trigger: +1
  In a paranoid interpretation, a local user or service with access to a virtual HCI or HCI injection path may be able to supply the malformed controller response.
* Broad/common subsystem exposure: +1
  Bluetooth is a common kernel subsystem on desktops, laptops, and mobile systems, although this specific path requires a local controller capability query.

Signals not awarded:

* Remote reachable / network-triggerable: +0
  The affected input is a local controller response, not a packet from a remote Bluetooth peer.
* Strong memory corruption: +0
  This is a limited read-only OOB condition, not an OOB write, UAF, double free, type confusion, or controlled overwrite.
* Privilege escalation plausible: +0
  No reclaim, write primitive, callback control, refcount abuse, or object replacement is supported by the patch.
* Reliable kernel crash / strong DoS: +0
  The patch describes a truncated response and one-byte overread into a cached list, not a reliable panic path.

## 3. Reachability analysis

The most realistic trigger is a malformed or malicious Bluetooth controller response to Read Local Codec Capabilities. This means the attacker generally needs influence over the local Bluetooth controller, firmware, emulation layer, or a privileged HCI injection path. It is not realistically triggerable by a normal remote Bluetooth peer based on this patch.

Namespaces and containers do not normally make raw HCI controller-event injection available to unprivileged users. If a product exposes virtual HCI or controller emulation to less trusted local users, the score should use the paranoid interpretation.

The path is present in the Bluetooth stack, but impact depends on Bluetooth being enabled and codec capability enumeration being executed.

## 4. Severity interpretation

This behaves like a low to borderline Moderate issue, not an Important-class vulnerability. The theoretical memory-safety concern is a small OOB read, but the demonstrated primitive is limited to copying one extra byte beyond an advertised controller response payload. There is no supported evidence of attacker-controlled memory corruption, privilege escalation, or remote network reachability.

The reason not to auto-close immediately is that the copied byte may become observable through codec capability reporting paths, so limited confidentiality impact should be checked.

## 5. One-sentence report phrase

A truncated Bluetooth HCI Read Local Codec Capabilities response can cause hci_read_codec_capabilities() to copy one byte beyond the advertised response payload into the cached codec list, creating a limited OOB read and possible low-impact information disclosure if attacker influence over a controller or HCI injection path exists.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

This should be manually checked because it is an OOB read candidate with a possible disclosure path, but it should not be treated as a Strong Important candidate without additional evidence of remote peer reachability, a larger disclosure primitive, or memory corruption beyond the one-byte read.

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UPSTREAM PATCH SUMMARY
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Patch: Bluetooth: hci: validate codec capability element length [ Upstream
Commit: fc97fc8cf7f53fd3619db63e09050d20a3a0c4b1
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=fc97fc8cf7f53fd3619db63e09050d20a3a0c4b1

Changed files:
  net/bluetooth/hci_codec.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=fc97fc8cf7f53fd3619db63e09050d20a3a0c4b1

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

The original Linux kernel CVE announcement for CVE-2026-74300 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74300

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:L/I:N/A:N
  The Best / paranoid CVSS vector: AV:L/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:L
  The Best / paranoid CVSS score: 4.4

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: 2
  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).