[CVE-2026-74540][MODERATE 7.0] Bluetooth: L2CAP: fix UAF in l2cap_le_connect_rsp [ Upstream

[CVE-2026-74540][MODERATE 7.0] Bluetooth: L2CAP: fix UAF in l2cap_le_connect_rsp [ Upstream

[AL-KERNEL]

CVE: CVE-2026-74540
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: Bluetooth: L2CAP: fix UAF in l2cap_le_connect_rsp [ Upstream
Commit: fd4c1e301bdec60a40728ea37de531cbccda501a
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=fd4c1e301bdec60a40728ea37de531cbccda501a
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74540
Analysis date: Sat, 15 Aug 2026 16:30:52 -0400
ActionableScore: 5
ActionableScore lower bound: 4
Actionable bucket: Strong Important candidate / Actionable Moderate at minimum
Manual review required: YES

Summary:
A Bluetooth L2CAP LE connect response handler can use a freed channel object after a remote disconnect race, allowing an adjacent Bluetooth attacker to trigger a kernel UAF with likely DoS impact and requiring manual review for possible memory corruption consequences.

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ABOUT THIS REPORT
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The original Linux kernel CVE announcement for CVE-2026-74540 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74540

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.

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AL-KERNEL CLASSIFICATION RESULT
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CVE-2026-74540	MODERATE	CHECK WITH IMPACT FROM ORIG NN IMPORTANT	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:A/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H';*CWE-416;CWE-362;CWE-667;Other CVSS 'AV:A/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:H';BEST CVSS score: '7.5';DESCR 'l2cap_le_connect_rsp() can use a Bluetooth L2CAP channel after it is freed because the handler looks up the channel by ident but did not take a reference before locking it. A nearby remote Bluetooth peer can race a LE connection response with a disconnect path that runs l2cap_chan_del(), freeing the channel between lookup and l2cap_chan_lock(). For the CVSS the PR:N is used because the attacker does not need a local account on the target, only Bluetooth adjacency and the ability to send protocol traffic to the exposed Bluetooth stack. The issue is not Internet reachable, but it is remotely reachable over Bluetooth radio range. Impact is at least denial of service via kernel crash and the paranoid score treats the UAF as possible kernel memory corruption with confidentiality, integrity, and availability impact.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 5)	YES	REMOTE LOCK UAF NETWORK  DECREASED_TO_MODERATE70_BASED_ON_ACTIONABLESCORELOWERTHAN6 DECREASED_TO_MODERATEREG_BASED_ON_FALSEPOSCHECKOFKP	NO	NO	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=5
ActionableScoreLower=4

## 1. ActionableScore

* Conservative score: 4
* Paranoid score: 5
* Final recommended bucket: **Strong Important candidate / Actionable Moderate at minimum**::

## 2. Signal breakdown

Conservative signals:

* Remote reachable / network-triggerable: +2
  Bluetooth L2CAP traffic can be sent by a nearby remote peer within radio range. This is not Internet reachable, but it is remotely reachable over an adjacent wireless protocol.

* Memory corruption, weak/indirect corruption candidate: +1
  The patch fixes a real UAF, but the shown primitive is a race between lookup and locking. No attacker-controlled reclaim, type confusion, callback control, or write-after-free primitive is demonstrated.

* Real lifetime corruption: +1
  The missing l2cap_chan_hold_unless_zero() means the channel lifetime was not protected after lookup, allowing l2cap_chan_del() to free it concurrently.

* Reliable kernel crash / strong DoS: +1
  A stale channel pointer can be locked and operated on after free, which is a credible kernel crash path.

* Hard or unreliable race / special timing required: -1
  Exploitation requires winning a race between LE connect response handling and remote disconnect driven channel deletion.

Conservative total before cap: 4
Race-UAF downgrade cap applies: conservative cap 4.

Paranoid additional signal:

* Broad/default/common endpoint exposure: +1
  Bluetooth is commonly present and enabled on many endpoint systems, so adjacent exposure may be practically relevant in non-server environments.

Paranoid total before cap: 5
Race-UAF downgrade cap applies: paranoid cap 5.

## 3. Reachability analysis

A nearby Bluetooth peer can potentially trigger the vulnerable path by interacting with the LE L2CAP connection state and racing a disconnect against l2cap_le_connect_rsp(). No local account on the victim is required, so this is not a local-only interface. The vector is adjacent wireless rather than Internet remote.

Namespaces and containers are not central to this issue because the attacker is external to the host over Bluetooth radio. Practical exposure depends on whether Bluetooth is enabled, discoverable or pairable state, controller policy, and whether the relevant L2CAP LE path is reachable by the attacker. The race requirement makes reliable exploitation harder, but the affected code is a real kernel object lifetime path.

Call-site confidence: high. The patch and commit directly show the lookup, missing hold, later lock/use, and added put.

## 4. Severity interpretation

This is not an ordinary Moderate resource leak or validation-only bug. It is an adjacent-reachable kernel UAF race in Bluetooth L2CAP handling. Realistic demonstrated impact is strongest for denial of service through kernel crash. Privilege escalation is theoretically possible for kernel UAF bugs, but the patch does not show reclaim control, writable stale access, function pointer dispatch, type confusion, or refcount takeover.

Therefore the conservative practical result is borderline/manual review at 4, while the paranoid result is Actionable Moderate at 5. It should not be auto-closed without human review because the bug class is UAF, the attacker can be external over Bluetooth adjacency, and the affected code is in the kernel networking stack.

## 5. One-sentence report phrase

A Bluetooth L2CAP LE connect response handler can use a freed channel object after a remote disconnect race, allowing an adjacent Bluetooth attacker to trigger a kernel UAF with likely DoS impact and requiring manual review for possible memory corruption consequences.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED.
YES REQUIRES MANUAL CHECK.

Reason: adjacent-reachable Bluetooth UAF race, real object lifetime bug, plausible kernel crash, and non-zero memory corruption concern even though a practical LPE primitive is not demonstrated.

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

Patch: Bluetooth: L2CAP: fix UAF in l2cap_le_connect_rsp [ Upstream
Commit: fd4c1e301bdec60a40728ea37de531cbccda501a
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=fd4c1e301bdec60a40728ea37de531cbccda501a

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=fd4c1e301bdec60a40728ea37de531cbccda501a

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

The original Linux kernel CVE announcement for CVE-2026-74540 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74540

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:H/PR:N/UI:N/S:U/C:L/I:L/A:H
  The Best / paranoid CVSS vector: AV:A/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H
  The Best / paranoid CVSS score: 7.5

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: 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).