[CVE-2026-72289][IMPORTANT] KVM: arm64: vgic: Check the interrupt is still ours before migrating it

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

CVE: CVE-2026-72289
Priority: IMPORTANT
AL-KERNEL base severity: IMPORTANT
KPANIC flag: YES
Patch: KVM: arm64: vgic: Check the interrupt is still ours before migrating it
Commit: 3893e1fcf6f306b327a8358dcd1cbd077989a240
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=3893e1fcf6f306b327a8358dcd1cbd077989a240
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72289
Analysis date: Sat, 15 Aug 2026 22:51:17 -0400
ActionableScore: 7
ActionableScore lower bound: 4
Actionable bucket: Strong Important candidate / Actionable Moderate at minimum
Manual review required: YES

Summary:
A race in KVM arm64 VGIC interrupt migration can double delete an interrupt from a vCPU pending list after it was concurrently removed, allowing a local guest or KVM user to trigger host kernel list corruption and at least a denial of service.

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

The original Linux kernel CVE announcement for CVE-2026-72289 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72289

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
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CVE-2026-72289	IMPORTANT	CHECK WITH IMPACT FROM ORIG NN LOW	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-787;*CWE-664;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '7';DESCR 'KVM arm64 vgic has a race in vgic_prune_ap_list while migrating a pending interrupt between vCPUs. The code drops locks and later checks only that the target affinity is unchanged, but the interrupt may already have been removed from the old ap_list by vgic_flush_pending_lpis while enabled and pending state still makes the affinity check pass. This can make list_del run a second time on an already removed list entry, leading to host kernel list corruption or a crash. For the CVSS the PR:L is used because the attacker typically needs the ability to run or control a guest VM or local KVM context, not full host administrator privileges. The issue is not directly network reachable and is a local or guest-to-host virtualization attack surface. Impact is at least denial of service on the host. For the paranoid score, choose the highest still defensible interpretation supported by the bug class and patch context, with preference for manual-review sensitivity over autoclosed false negatives.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 6)	YES	VIRT INIT SIMPLEFIX DMAorINTERRUPT HARDWARE LINUS  KPANIC INCREASED_TO_MODERATE_FROM_LOW_BASED_ON_GUESSCVSS KPANIC INCREASED_TO_HIGH_BASED_ON_ACTIONABLESCOREHIGHEREQTHAN6	NO	NO	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=7
ActionableScoreLower=4

## 1. ActionableScore

* Conservative score: 4
* Paranoid score: 7
* Final recommended bucket: **Strong Important candidate / Actionable Moderate at minimum**::

## 2. Signal breakdown

Conservative signals:

* Local unprivileged trigger: +1. Triggering appears possible from a local KVM guest or local user able to run/control a VM, typically not requiring full host root.
* Memory corruption, weak/indirect corruption candidate: +1. The bug can cause a second `list_del()` on an already removed VGIC interrupt list entry.
* Reliable kernel crash / strong DoS: +1. Kernel list corruption or invalid list manipulation can realistically crash the host.
* Broad/default/common subsystem exposure: +1. KVM is a common virtualization attack surface on arm64 systems where guests are supported.
* Hard or unreliable race / special timing required: -1. The bug requires a race between VGIC interrupt migration and pending LPI flushing.
* Privileged kernel/device-management memory corruption path: +1. The corruption occurs inside KVM VGIC interrupt management, a trusted host kernel virtualization path.

Paranoid additional interpretation:

* Memory corruption, strong corruption primitive: +2 instead of weak +1. A double `list_del()` can corrupt kernel list pointers, not merely cause a NULL dereference.
* Weak LPE concern: +1. Guest-to-host list corruption in KVM is a manual-review class even without a demonstrated reclaim or arbitrary write primitive.
* Real lifetime/ownership corruption: +1. The interrupt is no longer owned by the old vCPU list, but stale assumptions allow the old path to operate on it again.

## 3. Reachability analysis

The realistic trigger requires local KVM access or the ability to control a guest VM on an affected arm64 host. This is PR:L in practical terms, because `/dev/kvm` access is commonly delegated to non-root users or VM-management services, although exact reachability depends on host policy. It is not directly network reachable. A remote attacker would need an additional path to control a guest workload or VM-management interface.

Namespaces do not automatically make this reachable, but reduced-privilege service accounts, containerized VM managers, or users in the `kvm` group may have enough access. The race is timing dependent, so exploitation is not trivial, but the affected path is a real KVM host attack surface.

## 4. Severity interpretation

This is more than an ordinary Moderate because the failure mode is not just validation failure or a WARN. The patch prevents a stale ownership assumption that can make `list_del()` run twice on the same list node.

Realistically demonstrated impact is host DoS through list corruption or crash. Theoretical privilege escalation is not proven, because the patch does not show attacker-controlled reclaim, arbitrary write, callback control, or controlled object replacement. However, because this is KVM guest-to-host reachable list corruption in host kernel interrupt state, the paranoid score should remain high enough for manual review.

## 5. One-sentence report phrase

A race in KVM arm64 VGIC interrupt migration can double delete an interrupt from a vCPU pending list after it was concurrently removed, allowing a local guest or KVM user to trigger host kernel list corruption and at least a denial of service.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

Reason: this is a KVM guest-to-host attack surface with a race-dependent double `list_del()` and possible host kernel list corruption. Even though practical LPE is not demonstrated, this class should not be auto-closed.

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

Patch: KVM: arm64: vgic: Check the interrupt is still ours before migrating it
Commit: 3893e1fcf6f306b327a8358dcd1cbd077989a240
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=3893e1fcf6f306b327a8358dcd1cbd077989a240

Commit description:

vgic_prune_ap_list() drops both ap_list_lock and irq_lock while migrating
an interrupt to another vCPU. After reacquiring the locks it only checks
that the affinity is unchanged (target_vcpu == vgic_target_oracle(irq))
before moving the interrupt, which assumes that an interrupt whose affinity
is preserved is still queued on this vCPU's ap_list.

That assumption no longer holds if the interrupt is taken off the ap_list
while the locks are dropped. vgic_flush_pending_lpis() removes the
interrupt from the list and sets irq->vcpu to NULL, but leaves
enabled/pending/target_vcpu untouched. As the interrupt is still enabled
and pending, vgic_target_oracle() returns the same target_vcpu, so the
affinity check passes and list_del() is run a second time on an entry that
has already been removed.

Also check that the interrupt is still assigned to this vCPU
(irq->vcpu == vcpu) before moving it.

Fixes: 0919e84 ("KVM: arm/arm64: vgic-new: Add IRQ sync/flush framework")
Signed-off-by: Hyunwoo Kim <imv4bel@gmail.com>
Link: https://patch.msgid.link/aiHnI1mu6SGQrgnz@v4bel
Signed-off-by: Marc Zyngier <maz@kernel.org>
Cc: stable@vger.kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  arch/arm64/kvm/vgic/vgic.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=3893e1fcf6f306b327a8358dcd1cbd077989a240

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

The original Linux kernel CVE announcement for CVE-2026-72289 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72289

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: 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).