[CVE-2026-64404][MODERATE REGULAR] Bluetooth: ISO: avoid NULL deref of conn in iso_conn_big_sync()

[CVE-2026-64404][MODERATE REGULAR] Bluetooth: ISO: avoid NULL deref of conn in iso_conn_big_sync()

[AL-KERNEL]

CVE: CVE-2026-64404
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: Bluetooth: ISO: avoid NULL deref of conn in iso_conn_big_sync()
Commit: b3e647a4aa4d2d054f86a783f5c426035e1dc237
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=b3e647a4aa4d2d054f86a783f5c426035e1dc237
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64404
Analysis date: Sat, 25 Jul 2026 14:46:40 -0400
ActionableScore: 4
ActionableScore lower bound: 3
Actionable bucket: Borderline Moderate. Manual review recommended
Manual review required: YES

Summary:
A race in Bluetooth ISO `iso_conn_big_sync()` can dereference a NULL `conn` or `hcon` after the socket lock is dropped and reacquired during PA-sync teardown, allowing a local Bluetooth socket user with controller-event timing to crash the kernel.

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

The original Linux kernel CVE announcement for CVE-2026-64404 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64404

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.

======================================================================
AL-KERNEL CLASSIFICATION RESULT
======================================================================

CVE-2026-64404	MODERATE	CHECK WITH IMPACT FROM ORIG NN MODERATE	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H';**CWE-476;CWE-362;CWE-667;BEST CVSS score: '4.7';DESCR 'A race in Bluetooth ISO iso_conn_big_sync() can occur because the socket lock is dropped around hci_get_route() and the function later uses iso_pi(sk) conn hcon after taking the lock again. During this window the ISO connection can be torn down by controller driven disconnect handling, leaving conn or hcon NULL and causing a kernel NULL pointer dereference. For the CVSS the PR:L is used because reliable triggering requires a local process able to create or operate the relevant Bluetooth ISO PA sync socket. The issue is not reachable over an IP network, although Bluetooth controller events or nearby Bluetooth activity may participate in the teardown side of the race. Impact is denial of service via kernel crash. No direct evidence of UAF, information disclosure, or privilege escalation is visible from this patch context.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline Moderate. Manual review recommended (with actual score 4)	YES	REMOTE NULLPTR SIMPLEFIX RACE NETWORK  DECREASED_TO_MODERATE_REGULAR_FROM_MODERATE7_BASED_ON_GUESSCVSS_AND_CIANNH	YES	NO	checked

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

ActionableScore=4
ActionableScoreLower=3

## 1. ActionableScore

* Conservative score: 3
* Paranoid score: 4
* Final recommended bucket: **Borderline Moderate. Manual review recommended**::

## 2. Signal breakdown

Conservative signals:

* Local unprivileged trigger: +1. A local process that can create or operate the relevant Bluetooth ISO PA-sync socket can reach `iso_sock_recvmsg()` and the `iso_conn_big_sync()` path.
* Firmware-mediated external influence: +1. The teardown side of the race can be driven by Bluetooth controller events or nearby Bluetooth activity, but this is not ordinary IP network reachability.
* Reliable kernel crash / strong DoS: +1. If the race is won, `conn` or `conn->hcon` can be NULL and the kernel can hit a NULL pointer dereference.
* Broad/default/common subsystem: +1. Bluetooth is a common client subsystem, though the affected ISO PA-sync broadcast sink path is more specialized.
* Hard or unreliable race / special timing required: -1. The bug requires a dropped-lock timing window between `hci_get_route()` and re-acquiring the socket lock.

Paranoid additional interpretation:

* Availability impact realistic: +1. A successful trigger can cause a host-wide kernel crash, so the paranoid score keeps the issue above ordinary low-priority cleanup.

Not counted:

* No generic memory corruption. The patch and description support NULL dereference, not UAF reclaim, OOB write, double free, type confusion, or arbitrary write.
* No LPE signal. There is no demonstrated stale-object reuse, attacker-controlled reclaim, callback control, or write primitive.
* No confidentiality or integrity signal. The failure mode is crash-only based on the provided code path.

## 3. Reachability analysis

The likely trigger is a local process using Bluetooth ISO sockets in a PA-sync broadcast sink configuration with `BT_SK_DEFER_SETUP` and `BT_SK_PA_SYNC`. The race also depends on connection teardown occurring while the socket lock is dropped, which can be influenced by controller-side disconnect or broadcast teardown events.

This is not reachable over an IP network. It may be externally influenced over Bluetooth radio or controller behavior, but still appears to require a local socket context on the target. Namespaces and container impact are deployment-dependent because Bluetooth device access is commonly restricted, and many containers will not have direct host Bluetooth access. On desktops or embedded systems with Bluetooth enabled and permissive AF_BLUETOOTH access, the local trigger assumption is more plausible.

Call-site confidence: high. The commit message identifies `iso_sock_recvmsg()` as the reaching path and the patch shows the dereference site and the added revalidation.

## 4. Severity interpretation

This behaves like a borderline Moderate kernel DoS issue rather than an Important-class vulnerability. The theoretical risk comes from a race in kernel networking/Bluetooth code, but the concrete primitive shown is a NULL pointer dereference after connection teardown, not reusable memory corruption.

Realistic exploitation evidence supports denial of service only. Manual review is still useful because Bluetooth controller-mediated races can have subtle lifetime behavior, but the provided patch does not justify privilege escalation, confidentiality impact, or integrity impact.

## 5. One-sentence report phrase

A race in Bluetooth ISO `iso_conn_big_sync()` can dereference a NULL `conn` or `hcon` after the socket lock is dropped and reacquired during PA-sync teardown, allowing a local Bluetooth socket user with controller-event timing to crash the kernel.

## 6. Manual review recommendation

MANUAL CHECK RECOMMENDED

Reason: this is a kernel Bluetooth race with controller-mediated timing and a real crash path, but current evidence supports NULL dereference DoS only and does not show UAF reuse, write corruption, or privilege escalation.

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

Patch: Bluetooth: ISO: avoid NULL deref of conn in iso_conn_big_sync()
Commit: b3e647a4aa4d2d054f86a783f5c426035e1dc237
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=b3e647a4aa4d2d054f86a783f5c426035e1dc237

Commit description:

iso_conn_big_sync() drops the socket lock to call hci_get_route() and
then re-acquires it, but dereferences iso_pi(sk)->conn->hcon afterwards
without re-checking that conn is still valid.

While the lock is dropped, the connection can be torn down under the
same socket lock: iso_disconn_cfm() -> iso_conn_del() -> iso_chan_del()
sets iso_pi(sk)->conn to NULL (and the broadcast teardown path can also
clear conn->hcon on its own). When iso_conn_big_sync() re-acquires the
lock and reads conn->hcon, conn may be NULL, causing a NULL pointer
dereference (hcon is the first member of struct iso_conn).

This path is reached from iso_sock_recvmsg() for a PA-sync broadcast
sink socket (BT_SK_DEFER_SETUP | BT_SK_PA_SYNC), so the dropped-lock
window can race with connection teardown driven by controller events.

Re-validate iso_pi(sk)->conn and its hcon after re-acquiring the socket
lock and bail out if the connection went away, as already done in the
sibling iso_sock_rebind_bc().

Fixes: 7a17308 ("Bluetooth: iso: Fix circular lock in iso_conn_big_sync")
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=b3e647a4aa4d2d054f86a783f5c426035e1dc237

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

The original Linux kernel CVE announcement for CVE-2026-64404 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64404

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: Not available
  The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS score: 4.7

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: 3
  Paranoid ActionableScore: 4

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).