[CVE-2026-63946][MODERATE 7.0] Bluetooth: ISO: fix UAF in iso_recv_frame

[AL-KERNEL <alkernel@kernelcve.org>]

CVE: CVE-2026-63946
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: Bluetooth: ISO: fix UAF in iso_recv_frame
Commit: c57ea90f203c8b8b41a474f19a09000d0f841436
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=c57ea90f203c8b8b41a474f19a09000d0f841436
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-63946
Analysis date: Sun, 19 Jul 2026 22:48:21 -0400
ActionableScore: 5
ActionableScore lower bound: 4
Actionable bucket: Actionable Moderate at minimum
Manual review required: YES

Summary:
Bluetooth ISO receive handling can use a freed socket after dropping iso_conn_lock without holding a reference, allowing a race with iso_sock_kill that can crash the kernel and warrants manual review for UAF exploitability.

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

The original Linux kernel CVE announcement for CVE-2026-63946 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-63946

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-2026-63946	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:L/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:H';BEST CVSS score: '7.5';DESCR 'Bluetooth ISO receive handling has a race based use-after-free because iso_recv_frame reads the socket from conn under iso_conn_lock but uses it after dropping the lock without holding a socket reference. A concurrent iso_sock_kill can free the socket in that window, after which iso_recv_frame may read sk_state or pass the stale socket to sock_queue_rcv_skb(), leading to kernel memory corruption or a crash. For the CVSS the PR:N in the paranoid adjacent attack model means the attacker does not need a local account on the victim if timing is driven from a nearby Bluetooth peer, although reliable exploitation may depend on an existing ISO connection and socket teardown timing. The issue is not Internet reachable, but it is adjacent network reachable over Bluetooth radio range. Impact is at least denial of service and in the worst defensible case may include privilege escalation due to a kernel use-after-free.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate at minimum (with actual score 5)	YES	REMOTE DANGER UAF NETWORK SKB KPANIC  KPANIC DECREASED_TO_MODERATE70_BASED_ON_ACTIONABLESCORELOWERTHAN7	YES	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 score:

* Local unprivileged trigger: +1. A local process that can create and tear down Bluetooth ISO sockets may race socket close against receive handling.
* Memory corruption, weak primitive: +1. This is a race UAF, but the patch does not show controlled reclaim, type confusion, callback control, arbitrary write, or attacker-controlled object replacement.
* Real lifetime corruption: +1. The bug is a real missing socket reference lifetime issue, fixed by taking sock_hold under iso_conn_lock.
* Reliable kernel crash / strong DoS: +1. Dereferencing freed struct sock through sk_state or sock_queue_rcv_skb can plausibly crash the kernel.
* Availability impact realistic: +1. A kernel UAF in receive processing can produce host-wide DoS, not just a harmless warning.
* Hard or unreliable race / special timing required: -1. Triggering requires a narrow window between iso_recv_frame and concurrent iso_sock_kill.

Paranoid score differences:

* Adjacent network-triggerable influence: +2 instead of only local triggering. A nearby Bluetooth peer can influence frame delivery timing over radio range, although reliable exploitation likely still depends on an existing ISO connection and socket teardown timing.
* Race-UAF downgrade cap applied. Conservative score is capped at 4 and paranoid score at 5 because the patch only shows stale pointer survival across concurrent close/free, without a demonstrated reclaim or write primitive.

## 3. Reachability analysis

The most realistic trigger requires a local process able to use Bluetooth ISO sockets and cause socket teardown while ISO receive processing is active. A nearby Bluetooth peer may help drive receive-side timing, so the paranoid model treats this as adjacent network influenced, but not Internet reachable.

Namespaces and containers may matter if Bluetooth socket access is delegated into a container or service sandbox. This should not be treated as full host-root only unless the evaluated product restricts Bluetooth ISO sockets to administrators.

The path is not a broad TCP/IP Internet-facing path. It depends on Bluetooth ISO support, Bluetooth hardware or controller exposure, and an active ISO connection. These conditions reduce broad exposure, but the bug is still a kernel UAF in a receive path and should not be auto-closed.

## 4. Severity interpretation

This behaves like an actionable Moderate issue, with Important-class review sensitivity because it is a real kernel lifetime bug. The realistic impact is local or adjacent DoS via kernel crash. The theoretical higher concern is that struct sock UAF bugs can sometimes become privilege-escalation candidates, but this patch does not show controlled reclaim, stale object replacement, write-after-free, callback dispatch, or refcount takeover.

## 5. One-sentence report phrase

Bluetooth ISO receive handling can use a freed socket after dropping iso_conn_lock without holding a reference, allowing a race with iso_sock_kill that can crash the kernel and warrants manual review for UAF exploitability.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

Reason: this is a real race-based UAF in a Bluetooth receive path, with adjacent-radio influence possible and kernel crash impact likely, even though the patch does not demonstrate a strong LPE primitive.

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

Patch: Bluetooth: ISO: fix UAF in iso_recv_frame
Commit: c57ea90f203c8b8b41a474f19a09000d0f841436
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=c57ea90f203c8b8b41a474f19a09000d0f841436

Commit description:

iso_recv_frame reads conn->sk under iso_conn_lock but releases the lock
before using sk, with no reference held. A concurrent iso_sock_kill()
can free sk in that window, causing use-after-free on sk->sk_state and
sock_queue_rcv_skb().

Fix by replacing the bare pointer read with iso_sock_hold(conn), which
calls sock_hold() while the spinlock is held, atomically elevating the
refcount before the lock drops. Add a drop_put label so sock_put() is
called on all exit paths where the hold succeeded.

Fixes: ccf74f2 ("Bluetooth: Add BTPROTO_ISO socket type")
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/iso.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=c57ea90f203c8b8b41a474f19a09000d0f841436

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

The original Linux kernel CVE announcement for CVE-2026-63946 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-63946

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:H/PR:L/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: 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).