[CVE-2026-80683][MODERATE 7.0] Bluetooth: SCO: give the socket its own sco_conn reference

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

CVE: CVE-2026-80683
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: Bluetooth: SCO: give the socket its own sco_conn reference
Commit: a33bc07b4730b6cd5681ac77d18ae0de3e739690
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=a33bc07b4730b6cd5681ac77d18ae0de3e739690
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80683
Analysis date: Fri, 28 Aug 2026 03:51:35 -0400
ActionableScore: 5
ActionableScore lower bound: 4
Actionable bucket: Strong Important candidate / Actionable Moderate at minimum
Manual review required: YES

Summary:
A Bluetooth SCO reference ownership race can let close() overlap a controller Disconnection Complete event and trigger refcount underflow plus use after free in sco_conn_put(), causing a local kernel crash with manual review needed for possible LPE risk.

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ABOUT THIS REPORT
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The original Linux kernel CVE announcement for CVE-2026-80683 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80683

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-2026-80683	MODERATE	CHECK WITH IMPACT FROM ORIG NN IMPORTANT	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H';*CWE-416;CWE-362;CWE-911;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '7';DESCR 'Bluetooth SCO has a reference ownership bug where the socket stores sco_conn without holding its own counted reference and sco_conn_del() can drop an extra reference. When close() races the controller Disconnection Complete event, conn sk can become NULL while sco_conn_del() is still running, causing a refcount underflow and a use after free in sco_conn_put(). For the CVSS the PR:L is used because reliable triggering typically requires a local user or process able to create and close SCO sockets while the Bluetooth connection is being disconnected. The issue is primarily local, although the timing can involve an adjacent Bluetooth controller or peer event. Impact is at least denial of service via kernel crash. In the paranoid interpretation, the confirmed use after free may allow confidentiality or integrity impact and should be reviewed for privilege escalation risk.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 5)	YES	REMOTE OOB RACE LEAK ERRORPATH UAF NETWORK KPANIC  KPANIC DECREASED_TO_MODERATE70_BASED_ON_ACTIONABLESCORELOWERTHAN6	YES	NO	guess

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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:

* Firmware-mediated external influence: +1. The race involves the controller Disconnection Complete event, which can be influenced by Bluetooth controller or adjacent peer behavior.
* Local unprivileged trigger: +1. A local process able to create and close Bluetooth SCO sockets can participate in the race. If the evaluated product restricts SCO socket creation, this should be downgraded.
* Memory corruption, weak primitive: +1. The patch and KASAN trace show a use after free and refcount underflow, but no attacker-controlled reclaim, object replacement, callback control, or arbitrary write is demonstrated.
* Real lifetime corruption: +1. The bug is a real reference ownership and lifetime error involving sco_conn and hci_conn references.
* Reliable kernel crash / strong DoS: +1. The report shows KASAN slab-use-after-free and refcount underflow in a kernel workqueue path.
* Hard or unreliable race / special timing required: -1. Triggering requires a close() race with controller disconnection handling.

Conservative total: 4

Paranoid additional signal:

* Availability impact realistic: +1. Once the race is hit, the failure is host-kernel memory lifetime corruption with a credible crash path.

Paranoid total: 5

Not awarded:

* Privilege escalation plausible: +0. There is no shown reclaim primitive, controlled replacement, type confusion, callback dispatch, or arbitrary write.
* Remote reachable: +0. This is not a normal network-reachable protocol parser bug. The external component is Bluetooth/controller mediated.
* Strong memory corruption primitive: +0. Race-UAF downgrade applies because the patch only demonstrates lifetime/refcount misuse and crash, not controlled exploitation.

## 3. Reachability analysis

A local user or process must be able to open and manipulate Bluetooth SCO sockets and race close() with disconnection completion. The Bluetooth controller or an adjacent Bluetooth peer may help create the required disconnect timing, but the primary trigger is local. Containers only matter if Bluetooth device access or relevant socket permissions are delegated into the container. This path is common on Bluetooth-enabled desktop or embedded systems, but usually absent or disabled on many servers.

Call-site confidence: high. The patch includes the relevant ownership sites in __sco_chan_add(), sco_conn_del(), sco_connect(), sco_conn_ready(), and sco_connect_cfm().

## 4. Severity interpretation

This is more than an ordinary Moderate correctness fix because the patch documents a confirmed slab-use-after-free and refcount underflow. Realistic demonstrated impact is local kernel crash and denial of service. Theoretical privilege escalation is not proven, but the lifetime corruption is real enough to require manual review. The conservative result is borderline manual-review territory, while the paranoid score places it as Actionable Moderate at minimum and a weak Important candidate.

## 5. One-sentence report phrase

A Bluetooth SCO reference ownership race can let close() overlap a controller Disconnection Complete event and trigger refcount underflow plus use after free in sco_conn_put(), causing a local kernel crash with manual review needed for possible LPE risk.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED.
YES REQUIRES MANUAL CHECK.

Reason: confirmed UAF plus refcount underflow in a kernel Bluetooth lifetime path. The patch does not prove an LPE primitive, but this class should not be auto-closed without checking object reuse and triggerability on the target product.

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

Patch: Bluetooth: SCO: give the socket its own sco_conn reference
Commit: a33bc07b4730b6cd5681ac77d18ae0de3e739690
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=a33bc07b4730b6cd5681ac77d18ae0de3e739690

Commit description:

sco_conn_del() drops a reference it does not own. It takes one transient
reference via sco_conn_hold_unless_zero() and releases it with the
sco_conn_put() that follows sco_sock_hold(); the additional put in the
!sk branch releases a second one:

    conn = sco_conn_hold_unless_zero(conn);
    ...
    sk = sco_sock_hold(conn);
    sco_conn_unlock(conn);
    sco_conn_put(conn);

    if (!sk) {
            sco_conn_put(conn);
            return;
    }

When close() races the controller's Disconnection Complete, sco_chan_del()
clears conn->sk and drops the socket's reference while sco_conn_del() is
running. sco_conn_del() then sees sk == NULL, its own put drops the count
to zero and frees the conn, and the second put writes to the freed kref:

    BUG: KASAN: slab-use-after-free in sco_conn_put.part.0+0x1a/0x190
    Write of size 4 at addr ffff8881099dec74 by task kworker/u17:3/413
    Workqueue: hci1 hci_rx_work
    Call Trace:
     sco_conn_put.part.0+0x1a/0x190
     hci_disconn_complete_evt+0x1ee/0x3e0
     hci_event_packet+0x54a/0x650
     hci_rx_work+0x321/0x3d0
    Allocated by task 413:
     sco_conn_add+0x72/0x1a0
     sco_connect_cfm+0x88/0x670
    Freed by task 413:
     sco_conn_del.isra.0+0x3f/0xf0
     hci_disconn_complete_evt+0x1ee/0x3e0
    refcount_t: underflow; use-after-free.

The root cause is that the socket stores the connection without holding a
reference of its own. __sco_chan_add() does:

    sco_pi(sk)->conn = conn;

so the socket borrows whatever reference its caller happened to hold, and
the callers paper over that with ad-hoc holds and puts. Give the socket a
counted reference instead: __sco_chan_add() takes one and it is released
together with the channel (sco_chan_del()) and in sco_sock_destruct().
With the socket holding its own reference, sco_conn_del() no longer needs
the extra put and the redundant hold in sco_conn_ready() goes away.

Making the socket own its reference means the connection is now actually
freed on the error paths of sco_connect() where it used to leak, which in
turn runs sco_conn_free() and its hci_conn_drop(conn->hcon). To keep the
hci_conn accounting balanced, make that ownership explicit as well:
sco_conn_add() consumes one hci_conn reference and the sco_conn owns it for
its lifetime. sco_connect() hands over the reference returned by
hci_connect_sco() and no longer drops it on the error paths;
sco_connect_cfm(), which is not given a reference, takes one with
hci_conn_hold() before handing it to sco_conn_add() (and drops it again if
the allocation fails); and the explicit hci_conn_hold() in sco_conn_ready()
is removed. Every reference then has a single, clear owner.

Fixes: e672077 ("Bluetooth: SCO: Use kref to track lifetime of sco_conn")
Cc: stable@vger.kernel.org
Suggested-by: Pauli Virtanen <pav@iki.fi>
Signed-off-by: Aldo Ariel Panzardo <qwe.aldo@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/sco.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=a33bc07b4730b6cd5681ac77d18ae0de3e739690

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

The original Linux kernel CVE announcement for CVE-2026-80683 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80683

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