---
id: "CVE-2026-98720"
kind: "vulnerability"
aliases: ["CVE-2026-98720"]
title: "Linux KVM: nested VM entry can leave TPR writes passed through to L0"
severity: "unknown"
cvss: null
epss: null
exploited: false
status: "open"
category: "runtime"
products: []
ecosystems: []
tags: ["kvm", "linux-kernel", "nested-virtualization", "runtime", "self-hosted"]
not_affected_if: ["no-kvm", "no-nested-virtualization"]
published_at: "2026-10-18T16:17:25+00:00"
first_seen_at: "2026-10-23T21:57:16+00:00"
updated_at: "2026-10-25T05:17:24+00:00"
sources: [{"source": "nvd", "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-98720", "first_seen_at": "2026-10-23T21:57:16+00:00"}]
---

# Linux KVM: nested VM entry can leave TPR writes passed through to L0

The Linux kernel's KVM nested VMX code fails to refresh the vmcs02 MSR bitmap when eVMCS controls change between nested VM entries. A guest VM can then read and write the host's TPR (task priority register) directly.

_Summary, check and fix written by a model from the sources; labelled as such._

## How to check

- unknown

## Fix

- unknown

## Timeline

- 2026-10-23T21:57:16+00:00 nvd https://nvd.nist.gov/vuln/detail/CVE-2026-98720

## From the sources

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

KVM: nVMX: Force MSR bitmap refresh if runtime eVMCS controls are modified

Force a refresh of the vmcs02 MSR bitmap during nested VM-Enter if the
runtime eVMCS controls (pin, primary, secondary, etc.) are being updated.
If L1 isn't intercepting TPR writes, runs L2 with TPR virtualization, and
then runs the same L2 with TPR virtualization disabled, KVM will fail to
refresh msr_bitmap02 and leave TPR in passthrough mode even though TPR
virtualization is disabled.  I.e. failure to refresh the bitmap lets L2 (or
L1 by proxy) read and write L0's TPR.

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_Free to read at a human pace. An API with keys and an MCP server are in preparation; early access: hello@infrastack.ai_