[CVE-2026-80665][MODERATE REGULAR] KVM: arm64: nv: Inject SEA if kvm_translate_vncr() can't resolve PFN

[CVE-2026-80665][MODERATE REGULAR] KVM: arm64: nv: Inject SEA if kvm_translate_vncr() can't resolve PFN

[AL-KERNEL]

CVE: CVE-2026-80665
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: KVM: arm64: nv: Inject SEA if kvm_translate_vncr() can't resolve PFN
Commit: 4ead4def04659739c399bfcb063f8a906194c79f
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=4ead4def04659739c399bfcb063f8a906194c79f
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80665
Analysis date: Fri, 28 Aug 2026 06:59:59 -0400
ActionableScore: 4
ActionableScore lower bound: 3
Actionable bucket: Borderline. Manual review recommended
Manual review required: YES

Summary:
KVM arm64 nested virtualization can crash the host kernel when VNCR PFN translation fails without preparing a valid abort state, allowing a local KVM user or nested guest context to trigger a guest-to-host DoS without evidence of memory corruption or privilege escalation.

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

The original Linux kernel CVE announcement for CVE-2026-80665 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80665

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-2026-80665	MODERATE	CHECK WITH IMPACT FROM ORIG NN MODERATE	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:L/PR:L/UI:N/S:C/C:N/I:N/A:H';CWE-617;CWE-703;CWE-755;Other CVSS 'AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '6.5';DESCR 'KVM arm64 nested virtualization can crash the host when kvm_translate_vncr() returns EFAULT without preparing a valid s1_walk_result abort state. A late failure such as a VNCR translated GFN outside the memslots or an unresolved PFN can make kvm_handle_vncr_abort() reach BUG_ON() in the fault injection path. For the CVSS the PR:L value is used because reliable triggering requires the ability to run or control a VM or nested guest context through KVM, but does not require full host root privileges in typical tenant or /dev/kvm access models. The issue is not directly network reachable and is triggered through the virtualization control and guest execution path rather than packet traffic. Impact is denial of service via host kernel crash. No confidentiality or integrity impact is assigned because the patch indicates an error handling and reachable assertion failure rather than a concrete memory corruption primitive.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline. Manual review recommended (with actual score 4)  SKIP CVE-2026-80665 UNKNOWN SKIP The Fixes patch not applied yet, so unlikely that actual: url YES  NO NO unknown 	MAYBE	VIRT SIMPLEFIX HARDWARE LINUS  INCREASED_TO_MODERATE7_FROM_MODERATE_BASED_ON_GUESSCVSS DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5	-	-	checked

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

ActionableScore=4
ActionableScoreLower=3

## 1. ActionableScore

* Conservative score: 3
* Paranoid score: 4
* Final recommended bucket: **Borderline. Manual review recommended**::

## 2. Signal breakdown

* Local unprivileged trigger: +1. Triggering appears possible from a user or tenant able to run or control a KVM VM or nested guest, commonly via `/dev/kvm` access rather than full host root.
* Reliable kernel crash / strong DoS: +1. The old path could reach `BUG_ON(!vt->wr.failed)` and crash the host kernel.
* Cross-boundary isolation impact: +1. The failure is guest or nested-guest controlled behavior causing host-side KVM failure, affecting the virtualization boundary and potentially other workloads.
* Availability impact realistic: +1 in paranoid score only. Host kernel crash is system-wide if the BUG_ON path is reached.
* Rare AND difficult-to-reach subsystem/configuration: -1. This requires arm64 KVM nested virtualization and VNCR handling, which is not a broad default path.
* No memory corruption signal. The patch shows error-state preparation and removal of a reachable assertion, not UAF, OOB write, type confusion, refcount corruption, or arbitrary write.
* No confidentiality or integrity signal. There is no supported info leak or write primitive.

## 3. Reachability analysis

The likely attacker is a local user, VM tenant, or guest workload with enough access to exercise KVM arm64 nested virtualization. Full host root is not inherently required in environments where `/dev/kvm` is delegated to users or virtualization tenants, so PR:L is the better practical assumption for triage. Containers matter only if they are granted KVM device access. The path is not network reachable and is not triggered by packet traffic. Realistic exploitation depends on nested virtualization being enabled and on reaching the VNCR translation failure case, such as a translated GFN outside memslots or unresolved PFN.

## 4. Severity interpretation

This behaves like an actionable guest-to-host denial-of-service issue, not an Important-class memory corruption issue. The realistic impact is host kernel crash through a reachable `BUG_ON` after incomplete abort-state setup. Theoretical severity is elevated because the crash crosses the virtualization boundary, but the patch does not support privilege escalation, confidentiality impact, or integrity impact.

## 5. One-sentence report phrase

KVM arm64 nested virtualization can crash the host kernel when VNCR PFN translation fails without preparing a valid abort state, allowing a local KVM user or nested guest context to trigger a guest-to-host DoS without evidence of memory corruption or privilege escalation.

## 6. Manual review recommendation

MANUAL CHECK RECOMMENDED

This should not be auto-closed because it is a KVM guest-to-host host-crash condition, but the absence of a concrete memory corruption primitive keeps it below a Strong Important candidate.

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

Patch: KVM: arm64: nv: Inject SEA if kvm_translate_vncr() can't resolve PFN
Commit: 4ead4def04659739c399bfcb063f8a906194c79f
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=4ead4def04659739c399bfcb063f8a906194c79f

Commit description:

kvm_handle_vncr_abort() assumes that s1_walk_result conveys an abort
when kvm_translate_vncr() returns -EFAULT. This is not always the case
as it's possible to encounter 'late' failures on the output of S1
translation, e.g. a GFN outside of the memslots.

Fix it by preparing an external abort before returning from
kvm_translate_vncr(). Get rid of the BUG_ON() in the fault injection
path while at it.

Cc: stable@vger.kernel.org
Fixes: 2a359e0 ("KVM: arm64: nv: Handle mapping of VNCR_EL2 at EL2")
Signed-off-by: Oliver Upton <oupton@kernel.org>
Link: https://patch.msgid.link/20260618234207.1063941-3-oupton@kernel.org
Signed-off-by: Marc Zyngier <maz@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  arch/arm64/include/asm/kvm_nested.h
  arch/arm64/kvm/at.c
  arch/arm64/kvm/nested.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=4ead4def04659739c399bfcb063f8a906194c79f

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

The original Linux kernel CVE announcement for CVE-2026-80665 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80665

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:L/PR:L/UI:N/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS vector: AV:L/AC:L/PR:L/UI:N/S:C/C:N/I:N/A:H
  The Best / paranoid CVSS score: 6.5

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: 3
  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).