* [CVE-2026-90040][MODERATE 7.0] KVM: SEV: Forcefully invalidate SNP VMSA if its backing gmem page is zapped [ Upstream
@ 2026-09-16 13:30 21% AL-KERNEL
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From: AL-KERNEL @ 2026-09-16 13:30 UTC (permalink / raw)
To: kernel-cve
CVE: CVE-2026-90040
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: KVM: SEV: Forcefully invalidate SNP VMSA if its backing gmem page is zapped [ Upstream
Commit: 2640cc26ed0dd1bf6ec2f6852a60e494093db3e5
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=2640cc26ed0dd1bf6ec2f6852a60e494093db3e5
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-90040
Analysis date: Wed, 16 Sep 2026 09:30:18 -0400
ActionableScore: 5
ActionableScore lower bound: 4
Actionable bucket: Actionable Moderate / Strong Important candidate requiring manual review
Manual review required: YES
Summary:
No one-sentence report phrase was found.
======================================================================
ABOUT THIS REPORT
======================================================================
The original Linux kernel CVE announcement for CVE-2026-90040 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-90040
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.
======================================================================
AL-KERNEL CLASSIFICATION RESULT
======================================================================
CVE-2026-90040 MODERATE https://www.kernelcve.org/list/?q=CVE-2026-90040 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:U/C:L/I:L/A:H';*CWE-672;CWE-362;*CWE-664;Other CVSS 'AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '6.6';DESCR 'KVM SEV-SNP can keep a stale VMSA physical address in the vCPU control state when the guest_memfd page backing the guest provided VMSA is invalidated, for example by PUNCH_HOLE or memslot delete or move. If the vCPU keeps running with that VMSA page in use, firmware can reject RMPUPDATE reclaim with FAIL_INUSE and the page may later cause an RMP violation and host kernel crash. For the CVSS the PR:L is used because a local user or service with KVM VM control and access to the SNP guest_memfd can trigger the invalidation. The issue is not directly network reachable and requires an SEV-SNP KVM environment. Impact is at least local denial of service via host crash. For the paranoid score, limited confidentiality or integrity impact is kept as a manual review signal because stale protected page ownership and later host page reuse are involved, but the patch does not show an arbitrary write primitive.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate / Strong Important candidate requiring manual review (with actual score 5) YES OOB LOCK DANGER VIRT HARDWARE KPANIC YES NO checked
======================================================================
ACTIONABLESCORE ANALYSIS
======================================================================
ActionableScore=5
ActionableScoreLower=4
PrimitiveClass=CLASS_B
RealUAF=YES
HostAdminRequired=NO
NamespaceScopedPrivilege=NO
ImportantCandidate=YES
ManualReview=REQUIRED
AutoDowngradeAllowed=NO
1. ActionableScore
* Raw conservative score: 4
* Conservative score: 4. No floor or cap changed the score.
* Raw paranoid score: 5
* Paranoid score: 5. No floor or cap changed the score.
* Final recommended bucket: **Actionable Moderate / Strong Important candidate requiring manual review**::
2. Signal breakdown
Conservative signals:
* +2 Real lifetime or stale post-lifetime page use. KVM can keep a stale VMSA physical address in vCPU control state after the backing guest_memfd page is invalidated or zapped.
* +1 Reliable host crash or strong DoS. The supplied trace shows RMPUPDATE FAIL_INUSE followed by RMP violation and host kernel Oops in prep_new_page.
* +1 Active-state retirement and ownership invalidation bypass. A live VMSA page mapping must be invalidated when the backing gmem page or memslot is removed, but the old control.vmsa_pa could remain active.
Paranoid additional signal:
* +1 Active translation or protected-page synchronization concern. The stale VMSA page remains operationally active in SEV-SNP RMP state outside the immediate software structure, and the fix adds range invalidation and vCPU reload synchronization to prevent later host reuse under stale SNP ownership.
Non-awarded signals:
* +2 Strong guest-to-host exploitation leverage not awarded. The evidence supports host crash and stale protected page state, but not controlled host memory replacement, arbitrary host read or write, callback control, or demonstrated guest escape.
* Local unprivileged trigger not awarded. The complete trigger appears to require a local VMM or process with KVM VM control and guest_memfd operations, not an ordinary unprivileged user.
* Remote reachable not awarded. No network path is established.
* Extra Availability not awarded. The host crash is already counted once.
* Confidentiality and Integrity direct bonuses not awarded. Limited C/I concern is reflected only in the paranoid score because stale protected page ownership and host page reuse are involved, but no concrete disclosure or unauthorized write primitive is shown.
* Race penalty not awarded. The issue involves invalidation sequencing, but the supplied evidence does not establish a narrow externally uncontrollable timing race.
* Hardware rarity penalty not awarded. SEV-SNP capable hardware is required, but this is the relevant deployment environment for the vulnerable feature and not enough by itself to force a rare-hardware downgrade.
Repeated release/refcount check:
* First release can end lifetime: not applicable as a classic put or kref release sequence.
* Exact same reference survives: not as a refcounted object reference, but stale vmsa_pa survives in vCPU control state.
* Second lifetime/refcount mutation: not established.
* Concrete repeated release/refcount +1 awarded: no.
* Paranoid repeated-refcount +1 awarded: no.
* FLOOR 5 applied: no. The paranoid score reaches 5 by active protected-page synchronization concern, not by repeated-release floor.
3. Reachability analysis
The evaluated attacker is a local VMM or local host process with access to KVM VM control for an SEV-SNP guest. This actor can manage guest_memfd and trigger invalidation through operations such as PUNCH_HOLE or memslot delete or move. This is below host-admin in the practical KVM model when /dev/kvm and VM resources are delegated to a VMM process, so HostAdminRequired=NO.
This is not a guest-only trigger based on the supplied evidence. A malicious guest can provide or use the VMSA state, but the invalidation of the backing guest_memfd page or memslot lifecycle is controlled by the VMM or host-side process. Therefore the trigger is compound unless additional evidence shows the guest can induce the VMM-side invalidation.
NamespaceScopedPrivilege=NO because the relevant operations are KVM and guest_memfd VM lifecycle operations, not a namespace-scoped capability chain. Prior host setup exists in the sense that an SEV-SNP capable KVM environment and an SNP VM must exist, but exploitation does not appear to require host root once the VM control context is available. No direct network trigger is established.
Special hardware is required: AMD SEV-SNP capable virtualization. This narrows exposure but does not make the bug physical-only in the evaluated deployment. Race repeatability is not proven to be hard. The bug is primarily an invalidation and synchronization gap around live VMSA page state.
4. Primitive and severity interpretation
The exact primitive is stale active VMSA page state in KVM SEV-SNP. A guest-provided VMSA page from guest_memfd can be installed into vCPU control.vmsa_pa, and if the backing gmem page or relevant memslot is invalidated without forcing VMSA reload, KVM may continue to treat the stale physical page as the active VMSA.
This is active structured virtualization state, not fixed passive storage. It is broader than a simple WARN-only bug because the stale page ownership remains relevant to firmware RMP state and later host page allocation. The demonstrated consequence is host kernel crash by RMP violation. The speculative consequence is limited C/I impact from stale protected page ownership and later host reuse, but the patch does not establish arbitrary write, controlled reclaim, callback control, or guest-to-host privilege escalation.
PrimitiveClass=CLASS_B because this is a real lifetime or active-state ownership violation with unresolved exploitation leverage, but not a strong Class A primitive. RealUAF=YES because stale post-lifetime page use is directly implied after the backing gmem page is invalidated while vCPU control state may still consume it.
ImportantCandidate=YES because the bug affects KVM SEV-SNP protected page ownership and host page reuse, and the post-lifetime state is more meaningful than a shallow crash-only NULL dereference. AutoDowngradeAllowed=NO because automatic closure would discard an unresolved active-state lifetime and protected-page ownership primitive. Operational severity is Actionable Moderate, with Strong Important review justified if additional evidence shows guest-only triggering or useful host memory corruption beyond crash.
For KVM attacker roles:
* Guest-only: not established as complete trigger.
* Local VMM or /dev/kvm process: supported trigger model.
* Host administrator: not required by the supplied evidence once VM control is delegated.
* Actual guest-to-host corruption primitive: not established beyond host crash and stale protected page state.
5. One-sentence report phrase
KVM SEV-SNP can leave a stale VMSA physical address active after the backing guest_memfd page is invalidated, allowing a local VMM context to trigger RMP failures and a host kernel crash, with protected-page ownership state requiring manual review for possible impact beyond DoS.
6. Manual review recommendation
MANUAL CHECK REQUIRED
Reason: this is not merely a warning or ordinary crash path. It involves stale KVM SEV-SNP VMSA page state, guest_memfd invalidation, RMP ownership, and host page reuse, but the supplied evidence does not prove a controlled guest-to-host corruption primitive.
7. Call-site confidence
Call-site confidence: high
======================================================================
UPSTREAM PATCH SUMMARY
======================================================================
Patch: KVM: SEV: Forcefully invalidate SNP VMSA if its backing gmem page is zapped [ Upstream
Commit: 2640cc26ed0dd1bf6ec2f6852a60e494093db3e5
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=2640cc26ed0dd1bf6ec2f6852a60e494093db3e5
Changed files:
arch/x86/kvm/svm/sev.c
arch/x86/include/asm/kvm-x86-ops.h
arch/x86/include/asm/kvm_host.h
arch/x86/kvm/mmu/mmu.c
arch/x86/kvm/svm/svm.c
arch/x86/kvm/svm/svm.h
arch/x86/kvm/x86.c
include/linux/kvm_host.h
virt/kvm/guest_memfd.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=2640cc26ed0dd1bf6ec2f6852a60e494093db3e5
======================================================================
DETAILED REPORT METHODOLOGY
======================================================================
The original Linux kernel CVE announcement for CVE-2026-90040 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-90040
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:U/C:L/I:L/A:H
The Best / paranoid CVSS score: 6.6
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: 5
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 [email protected] (and both
send reply to CVE record itself too and see "reply" button below for howto reply).
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