[CVE-2026-74568][MODERATE 7.0] KVM: arm64: vgic: Fix race between LPI release and re-registration [ Upstream

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

CVE: CVE-2026-74568
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: KVM: arm64: vgic: Fix race between LPI release and re-registration [ Upstream
Commit: 292e80a159aa88635bf668a7212cfdf526b8bd52
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=292e80a159aa88635bf668a7212cfdf526b8bd52
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74568
Analysis date: Sat, 15 Aug 2026 18:10:59 -0400
ActionableScore: 7
ActionableScore lower bound: 5
Actionable bucket: Strong Important candidate / Actionable Moderate at minimum
Manual review required: YES

Summary:
A race in KVM arm64 VGIC LPI lifetime handling can let a guest-controlled LPI release and re-registration corrupt the LPI xarray state, causing DoS and creating a plausible stale-object or UAF candidate that requires manual review.

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ABOUT THIS REPORT
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The original Linux kernel CVE announcement for CVE-2026-74568 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74568

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-2026-74568	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:H/I:H/A:H';CWE-362;*CWE-416;*CWE-664;*CWE-772;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '7';DESCR 'A race in KVM arm64 VGIC LPI lifetime handling can occur when an LPI refcount reaches zero while another CPU re-registers the same INTID through vgic_add_lpi. The old code could separate the refcount drop from xarray eviction, allowing a newly registered LPI to be erased or an old LPI to be overwritten and leaked. This is at least a denial of service risk for the host or guest interrupt state, and the lifetime pattern around refcount, xarray replacement, and kfree_rcu makes it a plausible UAF or stale object candidate that needs manual review. For the CVSS the PR:L is used because an attacker typically needs control of a guest or a guest kernel path able to issue ITS LPI mapping commands, but full host administrative privileges are not required. The issue is not network reachable by packet traffic and is exposed through the KVM guest interrupt controller interface on arm64 systems using VGICv3 ITS and LPIs. Impact is at least availability loss, while the paranoid score uses CIA:HHH due to possible memory corruption consequences from the race class and patch context.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 7)	YES	VIRT RACE LEAK UAF HARDWARE LINUS  KPANIC INCREASED_TO_MODERATE7_BASED_ON_GUESSCVSS KPANIC INCREASED_TO_HIGH_BASED_ON_ACTIONABLESCOREHIGHEREQTHAN6 DECREASED_TO_MODERATE7_BASED_ON_FALSEPOSCHECKOFKP	YES	NO	checked

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ACTIONABLESCORE ANALYSIS
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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

Conservative signals:

* Local or guest-controlled trigger: +1. The race can be driven from guest-visible VGIC ITS LPI operations such as DISCARD and MAPTI, without host-root privileges.
* Memory corruption, weak or indirect corruption candidate: +1. The patch shows refcount and xarray lifetime inconsistency, stale LPI replacement, deletion of a newly registered object, and leaked orphaned objects.
* Real lifetime corruption: +1. The bug is explicitly about refcount drop, xarray eviction, kfree_rcu lifetime, and unsafe access after concurrent release.
* Reliable kernel crash or strong DoS: +1. Corrupting VGIC LPI state can break interrupt delivery and plausibly crash or destabilize the VM or host KVM path.
* Cross-boundary isolation concern: +1. The affected interface is a guest-to-host KVM interrupt-controller path, so a guest-controlled race affects host kernel state.
* Hard or unreliable race: -1. The issue requires a timing window between LPI release and re-registration on another CPU.
* Common virtualization exposure: +1. KVM arm64 VGICv3 ITS and LPIs are relevant for arm64 virtualization deployments using MSI-capable virtual devices.

Paranoid additional interpretation:

* Stronger memory-lifetime concern: +1 over conservative. The combination of refcount zero, xarray overwrite, kfree_rcu, and removal of pending_release because it is no longer safe from UAF makes this a credible UAF or stale-object manual-review candidate, even though no reclaim or arbitrary write primitive is demonstrated.

## 3. Reachability analysis

The bug is not network reachable by packet traffic. It is reachable through the KVM arm64 VGIC ITS LPI control path when a guest can cause concurrent LPI discard and re-map activity for the same INTID.

The practical attacker is most likely a malicious or compromised guest, possibly guest root or a guest kernel path that can issue the relevant ITS operations. This is not equivalent to full host-root privilege. Namespaces on the host are not the main factor here, but virtualization boundary exposure is important because guest-controlled state can affect host KVM data structures.

The path is configuration dependent: it needs arm64 KVM with VGICv3 ITS and LPIs. That is not universal on all Linux systems, but it is a normal virtualization configuration rather than a legacy-only path.

Call-site confidence: high. The provided commit message includes the relevant release and add paths, the race timeline, and the changed refcount/xarray/kfree_rcu logic.

## 4. Severity interpretation

This is above an ordinary Moderate because it is a KVM guest-facing lifetime race in host kernel code. The conservative evidence supports at least Actionable Moderate due to refcount lifetime corruption, xarray state corruption, and guest-to-host boundary impact.

Theoretical memory corruption potential is stronger than a plain DoS, but realistic exploitation evidence is not enough to claim reliable privilege escalation or arbitrary code execution. The paranoid score treats it as a Strong Important candidate because KVM object-lifetime races around refcounted RCU-freed objects have historically been under-triaged and should not be auto-closed.

## 5. One-sentence report phrase

A race in KVM arm64 VGIC LPI lifetime handling can let a guest-controlled LPI release and re-registration corrupt the LPI xarray state, causing DoS and creating a plausible stale-object or UAF candidate that requires manual review.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

Reason: this is a KVM guest-to-host refcount and object-lifetime race involving xarray replacement and kfree_rcu. No reliable LPE primitive is proven, but the bug class and boundary make it unsafe to auto-close.

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

Patch: KVM: arm64: vgic: Fix race between LPI release and re-registration [ Upstream
Commit: 292e80a159aa88635bf668a7212cfdf526b8bd52
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=292e80a159aa88635bf668a7212cfdf526b8bd52

Changed files:
  arch/arm64/kvm/vgic/vgic-its.c
  arch/arm64/kvm/vgic/vgic.c
  include/kvm/arm_vgic.h

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=292e80a159aa88635bf668a7212cfdf526b8bd52

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

The original Linux kernel CVE announcement for CVE-2026-74568 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74568

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: 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: 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).