[CVE-2026-64403][MODERATE 7.0] Bluetooth: L2CAP: validate option length before reading conf opt value

[CVE-2026-64403][MODERATE 7.0] Bluetooth: L2CAP: validate option length before reading conf opt value

[AL-KERNEL]

CVE: CVE-2026-64403
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: Bluetooth: L2CAP: validate option length before reading conf opt value
Commit: cca81b4bc672604a84f6d224a55cc77ec7dee619
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=cca81b4bc672604a84f6d224a55cc77ec7dee619
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64403
Analysis date: Sat, 25 Jul 2026 09:07:47 -0400
ActionableScore: 5
ActionableScore lower bound: 2
Actionable bucket: Actionable Moderate at minimum
Manual review required: NO

Summary:
A nearby Bluetooth peer can trigger a validate-after-use bug in L2CAP configuration parsing, causing l2cap_get_conf_opt() to read up to 4 bytes past the received option buffer before length validation, with realistic impact mainly limited to DoS or limited confidentiality concern.

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ABOUT THIS REPORT
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The original Linux kernel CVE announcement for CVE-2026-64403 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64403

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: 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-2026-64403	MODERATE	CHECK WITH IMPACT FROM ORIG NN LOW	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:N/A:H';CWE-125;*CWE-20;CWE-126;Other CVSS 'AV:A/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '7.1';DESCR 'A validate after use bug in Bluetooth L2CAP configuration parsing allows l2cap_get_conf_opt() to read opt val before confirming that the full attacker controlled option length is present in the buffer. A nearby remote Bluetooth peer can send a malformed L2CAP configuration option and trigger an out of bounds read of up to 4 bytes before the caller detects the malformed length. For the CVSS the PR:N is used because triggering does not require local privileges on the victim and only requires the ability to interact with the Bluetooth L2CAP path. The issue is adjacent network reachable rather than Internet reachable because Bluetooth proximity or link access is normally required. Impact is primarily denial of service or a hardened kernel warning. For the paranoid score, choose the highest still defensible interpretation supported by the bug class and patch context, with preference for manual review sensitivity over autoclosed false negatives. The worst case is limited confidentiality impact and high availability impact, not privilege escalation, because the patch shows an out of bounds read but not a write primitive or UAF.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate at minimum (with actual score 4)	YES	REMOTE OOB LEAK NETWORK HARDWARE  DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5	NO	NO	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=5
ActionableScoreLower=2

## 1. ActionableScore

* Conservative score: 2
* Paranoid score: 5
* Final recommended bucket: **Actionable Moderate at minimum**

## 2. Signal breakdown

Conservative signals:

* Network-triggerable via adjacent Bluetooth path: +2
  A nearby Bluetooth peer can send malformed L2CAP configuration options. This is not Internet-routable remote exposure, but it is externally triggerable over Bluetooth adjacency.

Paranoid additional signals:

* Confidentiality impact plausible: +1
  The primitive is a bounded OOB read of up to 4 bytes. The commit says the garbage value is not consumed in the current control flow, so this is not a demonstrated leak, but limited confidentiality concern is defensible for triage.

* Availability impact plausible: +1
  The malformed parser path may cause warning or crash behavior on hardened/debug kernels or if surrounding allocation layout changes, but reliable production DoS is not strongly demonstrated.

* Broad/default/common subsystem exposure: +1
  Bluetooth L2CAP is a common kernel protocol path on systems with Bluetooth enabled, especially laptops, desktops, mobile, and embedded devices.

Not counted:

* No generic strong memory corruption: +0
  The patch shows read-only OOB access, not OOB write, UAF, double free, type confusion, or refcount misuse.

* No privilege escalation plausible: +0
  No attacker-controlled reclaim, write primitive, callback control, or object replacement is shown.

* No Dirty-Pipe-like primitive: +0
  There is no shared page, COW, page-cache, or externally owned page write.

## 3. Reachability analysis

The bug is triggerable by a nearby Bluetooth peer able to interact with the L2CAP configuration path and send a malformed configuration option with an attacker-controlled option length. No local user account or privileges on the victim are required, but physical radio proximity or Bluetooth link reachability is normally required, so this is adjacent-network exposure rather than normal AV:N Internet exposure.

Namespaces and containers are not the main factor because the trigger is external Bluetooth protocol input, not a local syscall-only interface. The path is relevant only when Bluetooth is enabled and reachable. On servers with Bluetooth disabled or absent, exposure is negligible. On client and embedded systems with Bluetooth enabled, realistic triggering conditions are plausible.

Call-site confidence: high. The patch includes the helper and its direct callers: l2cap_parse_conf_req(), l2cap_parse_conf_rsp(), and l2cap_conf_rfc_get().

## 4. Severity interpretation

This behaves more like an actionable Moderate than a Strong Important issue. The concrete primitive is a small OOB read before validation, not a write or lifetime corruption. The current control flow reportedly prevents the read value from being consumed, which limits demonstrated confidentiality impact.

However, it should not be auto-closed as an ordinary low-risk cleanup because it is an externally triggerable Bluetooth kernel parser bug with a real validate-after-use ordering flaw. The paranoid score reaches Actionable Moderate because adjacent-network reachability plus a concrete OOB read deserves manual review, even though practical privilege escalation is not supported by the patch.

## 5. One-sentence report phrase

A nearby Bluetooth peer can trigger a validate-after-use bug in L2CAP configuration parsing, causing l2cap_get_conf_opt() to read up to 4 bytes past the received option buffer before length validation, with realistic impact mainly limited to DoS or limited confidentiality concern.

## 6. Manual review recommendation

MANUAL CHECK RECOMMENDED

Manual review is recommended because this is an adjacent-network reachable kernel protocol parser OOB read. It is not a strong Important candidate by itself, but the external trigger surface and concrete OOB read primitive make it unsuitable for automatic closure without checking product Bluetooth exposure and hardening behavior.

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

Patch: Bluetooth: L2CAP: validate option length before reading conf opt value
Commit: cca81b4bc672604a84f6d224a55cc77ec7dee619
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=cca81b4bc672604a84f6d224a55cc77ec7dee619

Commit description:

l2cap_get_conf_opt() derives the option length from the
attacker-controlled opt->len field and immediately dereferences
opt->val (as u8, get_unaligned_le16() or get_unaligned_le32(), or a
raw pointer for the default case) before any caller has confirmed
that opt->len bytes are present in the buffer. The callers
(l2cap_parse_conf_req(), l2cap_parse_conf_rsp() and
l2cap_conf_rfc_get()) only detect a malformed option afterwards, once
the running length has gone negative, by which point the
out-of-bounds read has already executed.

An existing post-hoc length check keeps the garbage value from being
consumed, so this is not a data leak in the current control flow. It
is still a validate-after-use ordering bug: up to 4 bytes are read
past the end of the buffer before it is known to contain them, and it
is fragile to future changes in the callers.

Fix it at the source. Pass the end of the buffer into
l2cap_get_conf_opt() and refuse to touch opt->val unless the full
option (header + value) fits. Each caller computes an end pointer
once before the loop and checks the return value directly instead of
inferring the error from a negative length.

Fixes: 7c9cbd0 ("Bluetooth: Verify that l2cap_get_conf_opt provides large enough buffer")
Cc: stable@vger.kernel.org
Signed-off-by: Muhammad Bilal <meatuni001@gmail.com>
Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  net/bluetooth/l2cap_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=cca81b4bc672604a84f6d224a55cc77ec7dee619

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

The original Linux kernel CVE announcement for CVE-2026-64403 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64403

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:N/I:N/A:L
  The Best / paranoid CVSS vector: AV:A/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:H
  The Best / paranoid CVSS score: 7.1

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: 2
  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: NO
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).