[CVE-2026-53256][MODERATE 7.0] Bluetooth: RFCOMM: hold listener socket in rfcomm_connect_ind() [ Upstream

[CVE-2026-53256][MODERATE 7.0] Bluetooth: RFCOMM: hold listener socket in rfcomm_connect_ind() [ Upstream

[AL-KERNEL]

CVE: CVE-2026-53256
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: Bluetooth: RFCOMM: hold listener socket in rfcomm_connect_ind() [ Upstream
Commit: f5ec76bdbeb80f75ad0be204371afffee0f8fac8
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=f5ec76bdbeb80f75ad0be204371afffee0f8fac8
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53256
Analysis date: Thu, 25 Jun 2026 09:02:02 -0400
ActionableScore: 5
ActionableScore lower bound: 4
Actionable bucket: Actionable Moderate at minimum
Manual review required: YES

Summary:
Bluetooth RFCOMM can race listener lookup against listener close, allowing `rfcomm_connect_ind()` to use a freed listener socket and potentially crash the kernel, with adjacent Bluetooth reachability and a weak but review-worthy UAF escalation concern.

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

The original Linux kernel CVE announcement for CVE-2026-53256 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53256

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-2026-53256	MODERATE	CHECK	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:N/I:N/A:H';BEST CVSS score: '7.5';DESCR 'A race in Bluetooth RFCOMM can leave rfcomm_connect_ind using a listener socket after it was closed and freed by another path. The selected listener was returned after dropping rfcomm_sk_list.lock without holding a reference, so close can unlink and free the parent before lock_sock, bt_accept_enqueue, or the deferred setup callback uses it. KASAN reported a slab use after free in lock_sock_nested, which makes this a memory safety issue rather than a pure DoS only bug. For the CVSS the PR:N is used for the paranoid score because an adjacent Bluetooth peer may trigger connection indications without local privileges on the victim, assuming a reachable RFCOMM listener and suitable Bluetooth access. The issue is not Internet reachable and should be treated as AV:A because exploitation requires Bluetooth proximity or access to the local Bluetooth network. Impact is at least denial of service via kernel crash and in worst case may allow confidentiality or integrity impact due to kernel use after free, so manual review is required.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate at minimum (with actual score 5)	YES	REMOTE LOCK INIT RACE UAF NETWORK TEST KPANIC MEMORY  KPANIC INCREASED_TO_HIGH_BASED_ON_GUESSCVSS KPANIC DECREASED_TO_MODERATE70_BASED_ON_ACTIONABLESCORELOWERTHAN7	NO	NO	checked

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

ActionableScore=5
ActionableScoreLower=4

## 1. ActionableScore

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

## 2. Signal breakdown

Conservative signals:

* Remote reachable / network-triggerable: +2. The trigger is not Internet-reachable, but an adjacent Bluetooth/RFCOMM peer can influence the connection indication path if an RFCOMM listener exists.
* Memory corruption, weak primitive: +1. KASAN reports slab-use-after-free in `lock_sock_nested()` from `rfcomm_connect_ind()`.
* Real lifetime corruption: +1. The listener socket can be freed after lookup because no reference was held across dropping `rfcomm_sk_list.lock`.
* Reliable kernel crash / strong DoS: +1. The reported failure is a concrete UAF crash path.
* Hard or unreliable race / special timing required: -1. Exploitation requires winning a close-vs-connect race.

Paranoid additional signal:

* Weak LPE concern: +1. The stale socket may be used not only for `lock_sock()` but also for queueing and possible `sk_state_change()` notification, so callback/function-pointer-adjacent use makes manual review justified, although no controlled reclaim or overwrite primitive is demonstrated.

## 3. Reachability analysis

An adjacent Bluetooth peer may trigger RFCOMM connection handling, while a local listener close path races with `rfcomm_connect_ind()`. No local privileges on the victim are necessarily required for the peer side, but the system must have Bluetooth/RFCOMM enabled and a reachable listener socket. This is not Internet-reachable and should be treated as adjacent-network exposure. Containers and namespaces are not the main factor here unless they can create or manage Bluetooth RFCOMM sockets on the host.

## 4. Severity interpretation

This is not an ordinary Moderate cleanup because it fixes a real UAF on a kernel `struct sock` object and KASAN observed the bug. Realistic impact is most clearly kernel crash / DoS due to the race window. Theoretical privilege escalation is not proven, but the stale object is used in sensitive socket operations and may reach a state-change callback path, so the paranoid score treats it as Actionable Moderate requiring manual review rather than auto-close.

## 5. One-sentence report phrase

Bluetooth RFCOMM can race listener lookup against listener close, allowing `rfcomm_connect_ind()` to use a freed listener socket and potentially crash the kernel, with adjacent Bluetooth reachability and a weak but review-worthy UAF escalation concern.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED. This is a confirmed race-triggered UAF in a remotely influenced Bluetooth socket path, with at least reliable DoS and enough stale-object usage to justify manual security review.

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

Patch: Bluetooth: RFCOMM: hold listener socket in rfcomm_connect_ind() [ Upstream
Commit: f5ec76bdbeb80f75ad0be204371afffee0f8fac8
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=f5ec76bdbeb80f75ad0be204371afffee0f8fac8

Changed files:
  net/bluetooth/rfcomm/sock.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=f5ec76bdbeb80f75ad0be204371afffee0f8fac8

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

The original Linux kernel CVE announcement for CVE-2026-53256 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53256

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:N/I:N/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: 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).