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Response snapshot Nov 5, 2026, 22:51 UTC

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VulnerabilityCVE-2026-23401

Linux kernel: KVM: x86/mmu: Drop/zap existing present SPTE even when creating an MMIO SPTE

In the Linux kernel, the following vulnerability has been resolved: KVM: x86/mmu: Drop/zap existing present SPTE even when creating an MMIO SPTE When installing an emulated MMIO SPTE, do so *after* dropping/zapping the existing SPTE (if it's shadow-present).

At a glance

Exploited
Not known
Severity
5.5 Medium (CVSS 3.1)
Chance of exploitation
Not estimated
Sources
1 source

What to do

Check the vendor advisory for affected versions and fixes.

Read NVD CVE-2026-23401 (opens a new tab)

What happened

In the Linux kernel, the following vulnerability has been resolved:

KVM: x86/mmu: Drop/zap existing present SPTE even when creating an MMIO SPTE

When installing an emulated MMIO SPTE, do so *after* dropping/zapping the existing SPTE (if it's shadow-present). While commit a54aa15c6bda3 was right about it being impossible to convert a shadow-present SPTE to an MMIO SPTE due to a _guest_ write, it failed to account for writes to guest memory that are outside the scope of KVM.

E.g. if host userspace modifies a shadowed gPTE to switch from a memslot to emulted MMIO and then the guest hits a relevant page fault, KVM will install the MMIO SPTE without first zapping the shadow-present SPTE.

Continue reading

------------[ cut here ]------------ is_shadow_present_pte(*sptep) WARNING: arch/x86/kvm/mmu/mmu.c:484 at mark_mmio_spte+0xb2/0xc0 [kvm], CPU#0: vmx_ept_stale_r/4292 Modules linked in: kvm_intel kvm irqbypass CPU: 0 UID: 1000 PID: 4292 Comm: vmx_ept_stale_r Not tainted 7.0.0-rc2-eafebd2d2ab0-sink-vm #319 PREEMPT Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 0.0.

0 02/06/2015 RIP: 0010:mark_mmio_spte+0xb2/0xc0 [kvm] Call Trace: <TASK> mmu_set_spte+0x237/0x440 [kvm] ept_page_fault+0x535/0x7f0 [kvm] kvm_mmu_do_page_fault+0xee/0x1f0 [kvm] kvm_mmu_page_fault+0x8d/0x620 [kvm] vmx_handle_exit+0x18c/0x5a0 [kvm_intel] kvm_arch_vcpu_ioctl_run+0xc55/0x1c20 [kvm] kvm_vcpu_ioctl+0x2d5/0x980 [kvm] __x64_sys_ioctl+0x8a/0xd0 do_syscall_64+0xb5/0x730 entry_SYSCALL_64_after_hwframe+0x4b/0x53 RIP: 0033:0x47fa3f </TASK> ---[ end trace 0000000000000000 ]---

Scores and how they were measured

CVSS base severity

5.5

Version 3.1As of

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

Measurement source (opens a new tab)

How bad it is if exploited. Not a prediction of exploitation or proof you are exposed.

EPSS probability

Not available

A model's estimate of exploitation in the next 30 days, not certainty or your own risk.

Related technology

Sources

  1. Primary source

    NVD CVE-2026-23401 (opens a new tab)

    NVD record: description, CVSS (the CNA score is preferred), affected products, and publication date. Not evidence of exploitation.

    Published Checked

  2. Primary source

    NVD CVE API 2.0 (opens a new tab)

    The NVD API page that supplied this CVE record.

    Published Date not suppliedChecked

Cite this record

For factual claims, cite the primary sources above; cite KEVWire for its compilation, dates, and classifications.

APA

KEVWire. (2026, November 5). Linux kernel: KVM: x86/mmu: Drop/zap existing present SPTE even when creating an MMIO SPTE (CVE-2026-23401). https://kevwire.com/record/CVE-2026-23401

MLA

"Linux kernel: KVM: x86/mmu: Drop/zap existing present SPTE even when creating an MMIO SPTE (CVE-2026-23401)." KEVWire, 5 Nov. 2026, kevwire.com/record/CVE-2026-23401.

Chicago

KEVWire. "Linux kernel: KVM: x86/mmu: Drop/zap existing present SPTE even when creating an MMIO SPTE (CVE-2026-23401)." Last modified November 5, 2026. https://kevwire.com/record/CVE-2026-23401.

Evidence summary (plain text)

Linux kernel: KVM: x86/mmu: Drop/zap existing present SPTE even when creating an MMIO SPTE (Apr 1, 2026).
In the Linux kernel, the following vulnerability has been resolved:

KVM: x86/mmu: Drop/zap existing present SPTE even when creating an MMIO SPTE

When installing an emulated MMIO SPTE, do so *after* dropping/zapping the
existing SPTE (if it's shadow-present).  While commit a54aa15c6bda3 was
right about it being impossible to convert a shadow-present SPTE to an
MMIO SPTE due to a _guest_ write, it failed to account for writes to guest
memory that are outside the scope of KVM.

E.g.
CVSS 5.5 (version 3.1; evidence as of Nov 5, 2026; https://nvd.nist.gov/vuln/detail/CVE-2026-23401).
Sources:
NVD CVE-2026-23401: https://nvd.nist.gov/vuln/detail/CVE-2026-23401
NVD CVE API 2.0: https://services.nvd.nist.gov/rest/json/cves/2.0?lastModStartDate=2026-11-05T20:51:23.450Z&lastModEndDate=2026-11-05T22:25:57.582Z&resultsPerPage=500&startIndex=1000
Record ID: CVE-2026-23401.
Record origin: Ingested record.
AI evidence: Not assessed.
Known exploitation: Not assessed.
Zero-day status: Not assessed. KEV membership alone does not establish zero-day status.
About this data

This record was ingested from a data source. Retrieved: Nov 5, 2026, 22:25 UTC. Ingestion is not an independent editorial investigation.

NVD status: Modified. Publication in the NVD is not evidence of exploitation.

A CISA KEV listing documents known exploitation, not necessarily a zero-day; absence from the catalog does not prove a vulnerability has never been exploited.

Technology tags indicate possible relevance, not verified exposure. Confirm the affected product, version, and configuration against your own inventory; KEVWire does not scan your systems.

A personal reading checklist on this device, not verified remediation.

Record JSON

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Record details

Record detail