[CVE-2026-74509][IMPORTANT] Bluetooth: hci_sync: Fix advertising data UAFs

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

CVE: CVE-2026-74509
Priority: IMPORTANT
AL-KERNEL base severity: IMPORTANT
KPANIC flag: YES
Patch: Bluetooth: hci_sync: Fix advertising data UAFs
Commit: 95cdcd8c82a501931fd3ae9b3811b0b6da167e94
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=95cdcd8c82a501931fd3ae9b3811b0b6da167e94
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74509
Analysis date: Sat, 15 Aug 2026 11:34:35 -0400
ActionableScore: 7
ActionableScore lower bound: 5
Actionable bucket: Strong Important candidate / Actionable Moderate at minimum
Manual review required: YES

Summary:
No one-sentence report phrase was found.

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

The original Linux kernel CVE announcement for CVE-2026-74509 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74509

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: IMPORTANT
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
======================================================================

CVE-2026-74509	IMPORTANT	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-667;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:H';BEST CVSS score: '7';DESCR 'A race in Bluetooth HCI advertising command sync paths can leave an adv_info pointer valid only under hdev lock in use after hci_remove_adv_instance frees it from an advertising termination event. KASAN shows a slab use-after-free write in hci_set_ext_scan_rsp_data_sync, so the impact is memory corruption with at least kernel crash risk and a plausible local privilege escalation risk that needs manual review. For the CVSS the PR:L is used because triggering generally requires local ability to manage Bluetooth advertising through mgmt or a Bluetooth service interface rather than full kernel administrative control. The issue is not a generic IP network bug. An adjacent Bluetooth peer may help create the termination event, but reliable exploitation generally needs local advertising control-plane activity. Impact is at least local denial of service and in the paranoid case may include confidentiality and integrity impact due to UAF memory corruption.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 7)	YES	REMOTE OOB DANGER UAF NETWORK SKB KPANIC 	NO	NO	checked

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

ActionableScore=7
ActionableScoreLower=5

1. ActionableScore
* Conservative score: 5
* Paranoid score: 7
* Final recommended bucket: **Strong Important candidate / Actionable Moderate at minimum**::

2. Signal breakdown
* Local unprivileged or low-privilege trigger: +1. Triggering requires local ability to manage Bluetooth advertising through mgmt or a Bluetooth service interface, not full kernel control.
* Generic memory corruption, strong primitive: +2. KASAN reports slab-use-after-free with a write in `hci_set_ext_scan_rsp_data_sync`.
* Real lifetime corruption: +1. An `adv_info` pointer can survive past `hci_remove_adv_instance()` and `kfree(adv)`.
* Reliable kernel crash / strong DoS: +1. The reported KASAN UAF write is a credible crash path.
* Weak LPE concern: +1. This is a writable stale object access, but no controlled reclaim, callback overwrite, or type confusion is shown.
* Hard or unreliable race: -1. Exploitation depends on interleaving command-sync wait with advertising termination.
* Paranoid only, confidentiality impact plausible: +1. UAF memory corruption can expose allocator-sensitive behavior in worst case.
* Paranoid only, integrity impact plausible: +1. A write-after-free into slab memory may corrupt another object if reuse is achievable.

3. Reachability analysis
The bug is local/control-plane reachable through Bluetooth advertising management paths. Direct mgmt access is often privileged, but real deployments may expose advertising control through BlueZ or service policy to a lower-privileged local user, so PR:L style handling is reasonable for triage. This is not a generic IP network vulnerability. An adjacent Bluetooth peer or controller-side event may help produce advertising termination, but reliable exploitation still appears to require local advertising setup and race timing. Bluetooth is common on endpoint systems but not universally enabled on servers.

Call-site confidence: high. The patch and commit show the affected call paths, the stale `adv_info` lifetime, the wait point, the freeing path, and the later UAF write.

4. Severity interpretation
This is more than ordinary Moderate because it is a real race-based UAF with a write to freed slab memory. Conservative handling is Actionable Moderate due to local reachability, race difficulty, and lack of a demonstrated reclaim primitive. Paranoid handling reaches Strong Important candidate because writable UAFs in kernel object lifetime code can sometimes become LPE-relevant even when the initial report only shows a crash.

5. One-sentence report phrase
A race in Bluetooth HCI advertising command-sync paths can keep an `adv_info` pointer across an HCI command wait after the instance is freed, causing a slab use-after-free write and possible kernel crash, with worst-case local privilege-escalation concern requiring manual review.

6. Manual review recommendation
MANUAL CHECK REQUIRED.
Reason: confirmed writable UAF in kernel Bluetooth code, plausible LPE concern, and nontrivial deployment-dependent privilege model.

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

Patch: Bluetooth: hci_sync: Fix advertising data UAFs
Commit: 95cdcd8c82a501931fd3ae9b3811b0b6da167e94
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=95cdcd8c82a501931fd3ae9b3811b0b6da167e94

Commit description:

hci_find_adv_instance() returns an adv_info pointer that is valid only
while hdev->lock is held.  The advertising command-sync paths perform
instance lookups without that lock and, in some cases, retain the pointer
while waiting for a controller response.

An advertising termination event can therefore interleave as follows:

  hci_cmd_sync_work                 hci_rx_work
  hci_find_adv_instance()
  __hci_cmd_sync_status()
    wait for controller reply       hci_dev_lock()
                                    hci_remove_adv_instance()
                                      kfree(adv)
  adv->scan_rsp_changed = false

KASAN reported:

  BUG: KASAN: slab-use-after-free in hci_set_ext_scan_rsp_data_sync+0x2e1/0x300
  Write of size 1 at addr ffff88810a45d21d by task kworker/u17:0/88
  Workqueue: hci0 hci_cmd_sync_work
  Call Trace:
   hci_set_ext_scan_rsp_data_sync+0x2e1/0x300
   hci_schedule_adv_instance_sync+0x390/0x4c0
   hci_cmd_sync_work+0x173/0x300
  Allocated by task 87:
   hci_add_adv_instance+0x538/0xac0
   add_advertising+0x885/0x1160
  Freed by task 89:
   kfree+0x131/0x3c0
   hci_remove_adv_instance+0x1d8/0x3b0
   hci_le_ext_adv_term_evt+0x17b/0x730

Protect the instance lookup and payload construction in the extended
advertising, scan response, and periodic advertising data paths.  Snapshot
the advertising parameters under hdev->lock, but release the lock before
waiting for the controller.

Clear advertising-data dirty bits before issuing their commands and
restore them after a failure using a fresh lookup.  Likewise, update the
reported transmit power through a fresh lookup after the parameter command
completes.  No adv_info pointer then survives an HCI command wait.

Fixes: cba6b75 ("Bluetooth: hci_sync: Make use of hci_cmd_sync_queue set 2")
Cc: stable@vger.kernel.org
Suggested-by: Luiz Augusto von Dentz <luiz.dentz@gmail.com>
Signed-off-by: Chengfeng Ye <nicoyip.dev@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/hci_sync.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=95cdcd8c82a501931fd3ae9b3811b0b6da167e94

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

The original Linux kernel CVE announcement for CVE-2026-74509 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74509

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: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: 5
  Paranoid ActionableScore: 7

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: IMPORTANT
KPANIC detected for this report: YES
Published priority for this report (same as in Subject): IMPORTANT

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).