[CVE-2026-53255][MODERATE REGULAR] Bluetooth: MGMT: validate advertising TLV before type checks [ Upstream

[CVE-2026-53255][MODERATE REGULAR] Bluetooth: MGMT: validate advertising TLV before type checks [ Upstream

[AL-KERNEL]

CVE: CVE-2026-53255
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: Bluetooth: MGMT: validate advertising TLV before type checks [ Upstream
Commit: 13ad995071a06570668dd8daab3616c247c72080
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=13ad995071a06570668dd8daab3616c247c72080
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53255
Analysis date: Thu, 25 Jun 2026 11:14:15 -0400
ActionableScore: 3
ActionableScore lower bound: 1
Actionable bucket: Borderline Moderate / manual review recommended
Manual review required: YES

Summary:
A malformed Bluetooth MGMT advertising TLV can cause `tlv_data_is_valid()` to read one byte past the supplied buffer before length validation, allowing a local management-path attacker to trigger a kernel OOB read and possible DoS, with no demonstrated privilege-escalation primitive.

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

The original Linux kernel CVE announcement for CVE-2026-53255 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53255

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
======================================================================

CVE-2026-53255	MODERATE	CHECK	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:H';CWE-125;*CWE-20;CWE-129;Other CVSS 'AV:L/AC:L/PR:H/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '6.1';DESCR 'A malformed Bluetooth advertising TLV can make tlv_data_is_valid() read the advertising type byte before proving that the current element still fits inside the supplied buffer. If the length byte is the last byte of the buffer, the parser reads one byte out-of-bounds while handling MGMT_OP_ADD_ADVERTISING and can trigger a kernel crash or KASAN report. For the CVSS the PR:L is used in the paranoid score because a local process may be able to reach the advertising management path through delegated Bluetooth management access or a privileged service interface, even though direct raw MGMT access is usually administrative. The issue is not directly network reachable because it is triggered through the local Bluetooth MGMT control path rather than over the air Bluetooth traffic. Impact is at least local denial of service via kernel crash, with limited confidentiality impact possible from an invalid read primitive but no supported integrity impact or privilege escalation primitive.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline Moderate / manual review recommended (with actual score 2)	YES	REMOTE READ KASAN OOB NETWORK  DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5	NO	NO	checked

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

ActionableScore=3
ActionableScoreLower=1

## 1. ActionableScore

* Conservative score: 1
* Paranoid score: 3
* Final recommended bucket: **Borderline Moderate / manual review recommended**::

## 2. Signal breakdown

Conservative signals:

* Reliable kernel crash / strong DoS: +1. KASAN reports vmalloc-out-of-bounds read in `tlv_data_is_valid()` from `MGMT_OP_ADD_ADVERTISING`.
* Requires admin/root/CAP_NET_ADMIN in typical deployments: -2. Direct Bluetooth MGMT control operations are normally administrative.
* Net result is floored to practical lower score 1 because this is still a kernel bounds bug, but with limited demonstrated impact.

Paranoid signals:

* Local unprivileged or reduced-privilege trigger concern: +1. A local process may reach this path indirectly through delegated Bluetooth management access or a privileged service interface.
* Reliable kernel crash / strong DoS: +1. The malformed TLV reaches a KASAN-detected out-of-bounds read and may crash or warn depending on kernel configuration.
* Confidentiality impact plausible: +1. The primitive is a one-byte out-of-bounds read, but no direct user-visible disclosure path is shown.
* No generic memory corruption bonus. This is read-only OOB, not UAF, OOB write, double-free, type confusion, or refcount corruption.
* No privilege escalation bonus. The patch does not show attacker-controlled overwrite, reclaim, callback dispatch, or object confusion.

## 3. Reachability analysis

The bug is triggered through the local Bluetooth MGMT control path, specifically malformed advertising TLV data passed to `MGMT_OP_ADD_ADVERTISING` via `hci_sock_sendmsg()`. It is not triggered by over-the-air Bluetooth packets and is not directly network reachable. Typical direct access requires administrative Bluetooth management privileges, but some systems may expose advertising control through `bluetoothd`, desktop policy, containers, or delegated service interfaces, which justifies the paranoid PR:L-style interpretation. The path requires Bluetooth support and an active management interface, so exposure is common on Bluetooth-enabled systems but not universal on servers.

## 4. Severity interpretation

This behaves like a borderline Moderate kernel memory-safety issue rather than an Important vulnerability. The demonstrated primitive is a one-byte out-of-bounds read before validation, with realistic impact mainly local DoS via KASAN report, warning, or crash. Theoretical confidentiality impact is limited and not clearly observable by the attacker. There is no evidence of integrity impact, privilege escalation, write primitive, UAF, or controllable memory corruption.

## 5. One-sentence report phrase

A malformed Bluetooth MGMT advertising TLV can cause `tlv_data_is_valid()` to read one byte past the supplied buffer before length validation, allowing a local management-path attacker to trigger a kernel OOB read and possible DoS, with no demonstrated privilege-escalation primitive.

## 6. Manual review recommendation

MANUAL CHECK RECOMMENDED

Reason: this is a kernel out-of-bounds read in a local control path and should not be blindly auto-closed, but the demonstrated primitive is narrow, read-only, mostly DoS-oriented, and does not currently justify Important-class handling.

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

Patch: Bluetooth: MGMT: validate advertising TLV before type checks [ Upstream
Commit: 13ad995071a06570668dd8daab3616c247c72080
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=13ad995071a06570668dd8daab3616c247c72080

Changed files:
  net/bluetooth/mgmt.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=13ad995071a06570668dd8daab3616c247c72080

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

The original Linux kernel CVE announcement for CVE-2026-53255 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53255

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:N/I:N/A:H
  The Best / paranoid CVSS vector: AV:L/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:H
  The Best / paranoid CVSS score: 6.1

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: 3

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).