[CVE-2026-92521][MODERATE REGULAR] ACPI: PCI: Clear driver_data on all paths that free the acpi_pci_root [ Upstream

[CVE-2026-92521][MODERATE REGULAR] ACPI: PCI: Clear driver_data on all paths that free the acpi_pci_root [ Upstream

[AL-KERNEL]

CVE: CVE-2026-92521
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: ACPI: PCI: Clear driver_data on all paths that free the acpi_pci_root [ Upstream
Commit: 321bb0eb1486a0d575f02e24e3f4170e408c2f51
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=321bb0eb1486a0d575f02e24e3f4170e408c2f51
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-92521
Analysis date: Fri, 18 Sep 2026 02:20:20 -0400
ActionableScore: 4
ActionableScore lower bound: unknown
Actionable bucket: Borderline / manual review recommended
Manual review required: YES

Summary:
No one-sentence report phrase was found.

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

The original Linux kernel CVE announcement for CVE-2026-92521 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-92521

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-2026-92521	MODERATE	https://www.kernelcve.org/list/?q=CVE-2026-92521 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:H/UI:N/S:U/C:H/I:H/A:H';*CWE-416;*CWE-664;CWE-825;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '6.4';DESCR 'A stale device driver_data pointer can remain after acpi_pci_root_add fails or after acpi_pci_root_remove frees an acpi_pci_root object. A later acpi_pci_find_root call may dereference the freed object and cause a kernel use after free. The confirmed impact is at least kernel crash or ACPI PCI hotplug failure. The worst case may include kernel memory corruption if the dangling object is reused before a later dereference. For the CVSS the PR:H is used because reliable triggering normally requires administrative control of PCI or ACPI hotplug operations or control of the relevant hardware firmware or virtual platform. The issue is not directly network reachable. Manual review is required to determine whether reachable post free accesses can provide an exploitable memory corruption primitive.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline / manual review recommended (with actual score 4)  SKIP CVE-2026-92521 UNKNOWN SKIP The Fixes patch not applied yet, so unlikely that actual: url YES  NO NO unknown 	MAYBE	DANGER ERRORPATH UAF HARDWARE MEMORY  DECREASED_TO_MODERATEREG_BASED_ON_FALSEPOSCHECKOFKP	-	-	checked

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

ActionableScore=4
PrimitiveClass=CLASS_B
RealUAF=YES
HostAdminRequired=UNKNOWN
NamespaceScopedPrivilege=UNKNOWN
ImportantCandidate=NO
ManualReview=RECOMMENDED
AutoDowngradeAllowed=YES

1. ActionableScore

* Raw conservative score: 3
* Conservative score: 4
* Raw paranoid score: 3
* Paranoid score: 4
* Applied conservative floor: Real UAF FLOOR 4 changes 3 to 4 because a freed acpi_pci_root remains reachable through device->driver_data and may be dereferenced later. Host-admin-equivalent privilege is not positively established.
* Applied paranoid floor: Real UAF FLOOR 4 changes 3 to 4 for the same reason.
* Final recommended bucket: **Borderline / manual review recommended**::

2. Signal breakdown

Positive signals:

* +2 Real UAF or active lifetime violation. The patch directly establishes that acpi_pci_root is freed while device->driver_data can still reference it. A subsequent acpi_pci_find_root call may dereference this stale pointer.
* +1 Reliable kernel crash or strong DoS concern. Dereferencing a freed structured kernel object can realistically cause an Oops, kernel crash, or ACPI PCI hotplug failure.

Negative signals:

* No host-admin penalty applied. The supplied patch does not positively establish that the complete trigger requires host-root-equivalent privileges.
* No hard-race penalty applied. The bug is an ordered lifetime failure after attach failure or root removal, not a demonstrated narrow timing race.
* No niche subsystem penalty applied. ACPI PCI root handling is platform dependent, but the input does not establish that the vulnerable condition is rare or unattacker-reachable.

Important non-awarded signals:

* Controlled reclaim or attacker-controlled replacement of the freed acpi_pci_root is not demonstrated.
* Arbitrary or directed kernel write is not demonstrated.
* Confidentiality and integrity impact are not awarded. A dangling pointer alone does not establish disclosure, modification, or privilege escalation.
* Remote reachability is not established. ACPI firmware, PCI root hot-add, and root removal are not direct network interfaces.
* Structured stale-object leverage is not awarded. The visible evidence establishes a later lookup and possible dereference, but does not show attacker-controlled post-free fields, callback dispatch, pointer traversal, or active reuse of a replacement object.
* No concrete repeated release, put, kfree, or refcount mutation through the same dangling reference is established.
* No additional Availability point is awarded because the possible Oops or crash is already counted once.

3. Reachability analysis

The stale pointer can arise on two paths: failure of dmar_device_add during ACPI PCI root hot-add, and removal of an ACPI PCI root bridge. The later stale use requires an acpi_pci_find_root call after the root has been freed but before driver_data is cleared.

The input does not establish which actor can reliably induce the complete root-bridge hot-add, attach failure, removal, and subsequent lookup sequence. Such events may be controlled by firmware, a hypervisor in a virtualized guest, hardware hotplug infrastructure, or an administrative management path. These possibilities do not establish either ordinary-user reachability or a host-admin requirement.

HostAdminRequired is therefore UNKNOWN. NamespaceScopedPrivilege is also UNKNOWN because no namespace-aware capability checks or complete namespace-scoped trigger chain are supplied. No direct network-triggerable path is shown. No concrete special hardware prerequisite is proven beyond the general ACPI PCI root and hotplug context.

There is no demonstrated attacker-controlled race. The issue is a stale pointer surviving an ordered error or removal path.

4. Primitive and severity interpretation

The exact primitive is a real stale post-free kernel object reference. acpi_pci_root is assigned to device->driver_data, freed by kfree on an add failure or root removal path, and can later be recovered through driver_data by acpi_pci_find_root.

This is an active structured-object UAF candidate rather than fixed stale DMA or buffer storage. However, the supplied patch only establishes a later possible stale dereference. It does not establish controlled object reuse, attacker-shaped replacement contents, a callback or ops dispatch through reused memory, arbitrary read or write, refcount takeover, or a security-boundary bypass.

This is not a repeated-release case. There is one kfree of root, but no visible second kfree, put, refcount decrement, or other lifetime-mutating operation through the same dangling reference. Therefore the concrete repeated release or refcount signal does not apply, and FLOOR 5 does not apply.

PrimitiveClass is CLASS_B because a real post-lifetime dereference candidate exists. The demonstrated practical consequence is kernel instability or DoS. Memory-corruption escalation is theoretically possible for a UAF if reclaimed memory is later interpreted as acpi_pci_root, but that mechanism is not established by the supplied patch. ImportantCandidate is NO because the available evidence is consistent with a constrained stale-object dereference without demonstrated reuse leverage. AutoDowngradeAllowed is YES because no unresolved controlled corruption, repeated lifetime mutation, authorization bypass, or cross-boundary primitive is shown.

Likely operational severity is Borderline Moderate. It should be manually reviewed for reachable acpi_pci_find_root callers and for platform or virtualization paths that could make root removal or hot-add failure attacker-influenced.

5. One-sentence report phrase

A stale device driver_data pointer may reference a freed acpi_pci_root after ACPI PCI root add failure or removal, allowing a later acpi_pci_find_root lookup to dereference freed kernel memory and cause a kernel crash.

6. Manual review recommendation

MANUAL CHECK RECOMMENDED

Review reachable acpi_pci_find_root call sites and determine whether an untrusted VM, firmware-facing device path, or delegated PCI hotplug management interface can induce the free followed by a later lookup.

7. Call-site confidence

Call-site confidence: medium

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

Patch: ACPI: PCI: Clear driver_data on all paths that free the acpi_pci_root [ Upstream
Commit: 321bb0eb1486a0d575f02e24e3f4170e408c2f51
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=321bb0eb1486a0d575f02e24e3f4170e408c2f51

Changed files:
  drivers/acpi/pci_root.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=321bb0eb1486a0d575f02e24e3f4170e408c2f51

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

The original Linux kernel CVE announcement for CVE-2026-92521 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-92521

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:H/UI:N/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS vector: AV:L/AC:H/PR:H/UI:N/S:U/C:H/I:H/A:H
  The Best / paranoid CVSS score: 6.4

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: unknown
  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).