[CVE-2026-53254][MODERATE 7.0] Bluetooth: RFCOMM: validate skb length in MCC handlers [ Upstream

[CVE-2026-53254][MODERATE 7.0] Bluetooth: RFCOMM: validate skb length in MCC handlers [ Upstream

[AL-KERNEL]

CVE: CVE-2026-53254
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: Bluetooth: RFCOMM: validate skb length in MCC handlers [ Upstream
Commit: 7c15c7c2878957cbfed93bcc29c13fdace464254
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=7c15c7c2878957cbfed93bcc29c13fdace464254
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53254
Analysis date: Thu, 25 Jun 2026 10:38:26 -0400
ActionableScore: 5
ActionableScore lower bound: 4
Actionable bucket: Actionable Moderate at minimum
Manual review required: YES

Summary:
A malicious nearby Bluetooth device can send truncated RFCOMM MCC frames that cause kernel out-of-bounds reads in MCC handlers, making this an adjacent-network Actionable Moderate issue requiring manual review.

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

The original Linux kernel CVE announcement for CVE-2026-53254 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53254

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-2026-53254	MODERATE	CHECK	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:A/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:H';CWE-125;*CWE-20;CWE-754;Other CVSS 'AV:A/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:L';BEST CVSS score: '7.6';DESCR 'A length validation flaw in Bluetooth RFCOMM MCC handling allows skb data to be interpreted as protocol specific structures before the skb length is checked. A malicious nearby Bluetooth device can send truncated MCC frames and trigger out of bounds reads in handlers such as rfcomm_recv_pn, rfcomm_recv_rpn, rfcomm_recv_rls, and rfcomm_recv_msc. For the CVSS the PR:N is used because no privileges are required on the victim beyond the ability to reach and interact with the Bluetooth RFCOMM endpoint. The attack vector is AV:A because exploitation requires Bluetooth adjacency rather than Internet reachability. Impact is at least limited confidentiality exposure or denial of service from invalid kernel reads. In the paranoid score, limited integrity impact and high availability impact are kept for manual review sensitivity, but the bug is not treated as arbitrary memory corruption because the patch shows reads and validation fixes rather than writes or UAF.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate at minimum (with actual score 5)	YES	REMOTE OOB NETWORK SKB HARDWARE KPANIC MEMORY  KPANIC INCREASED_TO_MODERATE7_BASED_ON_GUESSCVSS	NO	NO	checked

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

ActionableScore=5
ActionableScoreLower=4

## 1. ActionableScore

* Conservative score: 4
* Paranoid score: 5
* Final recommended bucket: **Actionable Moderate at minimum**

## 2. Signal breakdown

* Remote reachable / network-triggerable: +2
  Bluetooth RFCOMM is reachable from a malicious nearby Bluetooth device. This is adjacent-network style exposure, not Internet-reachable AV:N.
* Weak corruption / read-only OOB: +0
  The patch shows out-of-bounds reads from skb data after truncated MCC frames. It does not show OOB write, UAF, double free, type confusion, or arbitrary write.
* Confidentiality impact plausible: +1
  OOB read in kernel protocol parsing can plausibly expose or consume adjacent kernel buffer data, although no strong disclosure channel is demonstrated.
* Broad/default/common subsystem exposure: +1
  Bluetooth RFCOMM is a common kernel protocol path on systems with Bluetooth enabled.
* Paranoid availability concern: +1
  Invalid OOB reads in kernel packet parsing may cause crash or warning-dependent DoS on hardened/debug builds or unlucky object layout, but this is not strongly demonstrated.

## 3. Reachability analysis

A malicious nearby Bluetooth device can trigger the bug by sending truncated RFCOMM MCC frames. No local user account or victim-side privileges are required once the attacker can interact with the Bluetooth RFCOMM endpoint, so PR:N is appropriate for practical triage. This is not Internet-reachable and should be treated as adjacent Bluetooth exposure. Containers and namespaces are mostly irrelevant because the trigger is external Bluetooth protocol input. Realistic exploitation requires Bluetooth enabled, RFCOMM reachable, and attacker proximity or access to the same Bluetooth radio environment.

## 4. Severity interpretation

This is more than an ordinary Moderate because it is externally triggerable through Bluetooth protocol parsing in kernel space. It is not a strong Important candidate on the patch evidence alone because the primitive is read-only OOB access, not UAF, OOB write, type confusion, or controlled memory corruption. The realistic impact is limited information exposure or malformed-state handling, with possible DoS. The paranoid score keeps it actionable because adjacent network kernel parsing bugs are often underestimated during early triage.

## 5. One-sentence report phrase

A malicious nearby Bluetooth device can send truncated RFCOMM MCC frames that cause kernel out-of-bounds reads in MCC handlers, making this an adjacent-network Actionable Moderate issue requiring manual review.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

Reason: adjacent-network reachable kernel OOB read in Bluetooth protocol parsing. No strong LPE primitive is shown, but external reachability and kernel memory access make auto-close inappropriate.

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

Patch: Bluetooth: RFCOMM: validate skb length in MCC handlers [ Upstream
Commit: 7c15c7c2878957cbfed93bcc29c13fdace464254
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=7c15c7c2878957cbfed93bcc29c13fdace464254

Changed files:
  net/bluetooth/rfcomm/core.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=7c15c7c2878957cbfed93bcc29c13fdace464254

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

The original Linux kernel CVE announcement for CVE-2026-53254 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53254

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:A/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:L
  The Best / paranoid CVSS vector: AV:A/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:H
  The Best / paranoid CVSS score: 7.6

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: 5

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).