* [CVE-2026-98928][MODERATE REGULAR] KVM: arm64: Derive GUEST_HAS_SVE from the SVE feature bit at EL2 [ Upstream
@ 2026-10-27 4:28 21% AL-KERNEL
0 siblings, 0 replies; 1+ results
From: AL-KERNEL @ 2026-10-27 4:28 UTC (permalink / raw)
To: kernel-cve
CVE: CVE-2026-98928
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: KVM: arm64: Derive GUEST_HAS_SVE from the SVE feature bit at EL2 [ Upstream
Commit: 4efda204087145d40a84344edec7e9d3885ad3ab
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=4efda204087145d40a84344edec7e9d3885ad3ab
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98928
Analysis date: Tue, 27 Oct 2026 00:28:18 -0400
ActionableScore: 3
ActionableScore lower bound: unknown
Actionable bucket: Borderline / manual review recommended
Manual review required: YES
Summary:
A below-host-admin `/dev/kvm` process can create inconsistent arm64 pKVM SVE state that is later consumed by the EL2 world switch, causing a host-wide fault.
======================================================================
ABOUT THIS REPORT
======================================================================
The original Linux kernel CVE announcement for CVE-2026-98928 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98928
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-2026-98928 MODERATE https://www.kernelcve.org/list/?q=CVE-2026-98928 CHECK WITH IMPACT FROM ORIG NN MODERATE | AEGIS IMPACT MODERATE_KPANIC AEGIS_AS=1 LEGACY=MODERATE RESULT=DIFF (final Legacy and Aegis differ; FINAL: MODERATE, Aegis: MODERATE_KPANIC) Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H';**CWE-476;CWE-665;CWE-670;BEST CVSS score: '5.5';DESCR 'An arm64 pKVM feature state inconsistency can set KVM_ARCH_FLAG_GUEST_HAS_SVE while KVM_ARM_VCPU_SVE is clear. pkvm_vcpu_init_sve then leaves sve_state NULL, but vcpu_has_sve reports SVE as enabled and the world switch can load guest SVE state through that NULL pointer. The supported impact is an EL2 fault and host wide denial of service. No UAF, OOB write, arbitrary write, or reliable information disclosure primitive is established. For the CVSS the PR:L value is selected because reliable triggering normally requires a local process with access to /dev/kvm and control over VM or vCPU initialization. The issue is not directly network reachable and applies only to arm64 KVM systems using the affected pKVM paths. Automated impact decision path. The original SimpleNet classifier selected MODERATE. The primary LLM estimated paranoid CVSS 5.5 and the production ActionableScore returned 3 with recommendation Borderline / manual review recommended. The production rules then evaluated CVSS thresholds and ActionableScore thresholds. No severity changing production threshold or specialist override was recorded. The legacy KP specialist has no review artifact for this run. The legacy FD or DH downgrade specialist has no review artifact for this run. Exact triggered rule markers were V41_INHERITED_KPANIC_PROMOTION_BLOCKED and MANUAL_REVIEW_REQUIRED. The independent weaker Aegis shadow evaluated CVSS 2.6 and ActionableScore 1 with primitive class CLASS_C and manual review REQUIRED. Its independently reconciled impact was MODERATE_KPANIC. The models disagreed but the aggregation rules retained the production result. The final reported impact is MODERATE.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline / manual review recommended (with actual score 3) MAYBE DANGER VIRT SIMPLEFIX HARDWARE LINUS TEST V41_INHERITED_KPANIC_PROMOTION_BLOCKED MANUAL_REVIEW_REQUIRED - - checked
======================================================================
ACTIONABLESCORE ANALYSIS
======================================================================
ActionableScore=3
PrimitiveClass=CLASS_C
RealUAF=NO
HostAdminRequired=NO
NamespaceScopedPrivilege=NO
ImportantCandidate=NO
ManualReview=RECOMMENDED
AutoDowngradeAllowed=YES
RequiresHostUID0=NO
AuthorizationDecisionBypass=NO
ProtectedResourceImpact=NONE
B4PendingReview=NO
B4PendingConfirmed=NO
1. ActionableScore
* Raw base score: 3.
* Conservative score: 3; no floor or cap applied.
* Raw paranoid score: 3.
* Paranoid score: 3; no technically supported stronger primitive.
* Final recommended bucket: **Borderline / manual review recommended**::
2. Signal breakdown
* +1 weak/indirect state-corruption concern: independently derived SVE flag and feature bit can leave an active vCPU claiming SVE while `sve_state` is NULL.
* +1 reliable kernel/host DoS: the world switch subsequently attempts to load guest SVE state through that NULL pointer, supporting an EL2 fault and host-wide failure.
* +1 local below-host-admin trigger: supplied evidence grounds triggering in a local process with `/dev/kvm` access and VM/vCPU initialization control.
* No UAF, OOB write, repeated release, arbitrary write, controlled reclaim, disclosure, or authorization bypass is shown.
* No extra availability point: host-wide failure is the same crash already counted.
* No guest-to-host corruption bonus: a malicious guest-only trigger and a useful host-memory primitive are not established.
* No race, hardware-rarity, or host-admin penalty is applied without specific proof.
3. Reachability analysis
The evidenced actor is a local VMM process with `/dev/kvm` access, not guest code alone. That actor controls VM/vCPU feature initialization; the host kernel and EL2 world-switch code consume the inconsistent state. Numeric UID 0 and host-administrator capabilities are not required by the supplied evidence. No namespace capability participates, and no remote path is shown. Arm64 pKVM and affected SVE setup are required, but the evidence does not justify a rare-hardware penalty.
4. Primitive and severity reading
The primitive is active vCPU feature-state inconsistency followed by NULL-state consumption in privileged EL2 execution. It is neither stale storage nor a lifetime violation. The supported outcome is a host-wide fault/DoS; useful non-crash corruption, host memory access, escape, or confidentiality/integrity impact is unproven. This is CLASS_C rather than CLASS_B/A, so it is not an Important candidate and may be downgraded after review.
5. One-sentence report phrase
A below-host-admin `/dev/kvm` process can create inconsistent arm64 pKVM SVE state that is later consumed by the EL2 world switch, causing a host-wide fault.
6. Manual review advice
MANUAL CHECK RECOMMENDED
Confirm affected pKVM/SVE configurations and `/dev/kvm` exposure; no Important-preserving primitive is currently shown.
7. Call-site confidence
Call-site confidence: medium
======================================================================
UPSTREAM PATCH SUMMARY
======================================================================
Patch: KVM: arm64: Derive GUEST_HAS_SVE from the SVE feature bit at EL2 [ Upstream
Commit: 4efda204087145d40a84344edec7e9d3885ad3ab
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=4efda204087145d40a84344edec7e9d3885ad3ab
Changed files:
arch/arm64/kvm/hyp/nvhe/pkvm.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=4efda204087145d40a84344edec7e9d3885ad3ab
======================================================================
DETAILED REPORT METHODOLOGY
======================================================================
The original Linux kernel CVE announcement for CVE-2026-98928 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98928
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: Not available
The Best / paranoid CVSS vector: AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
The Best / paranoid CVSS score: 5.5
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: unknown
Paranoid ActionableScore: 3
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 [email protected] (and both
send reply to CVE record itself too and see "reply" button below for howto reply).
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