---
id: "CVE-2026-99168"
kind: "vulnerability"
aliases: ["CVE-2026-99168"]
title: "Linux kernel: mshv_vtl mmap path can dereference a NULL register page"
severity: "unknown"
cvss: null
epss: null
exploited: false
status: "open"
category: "runtime"
products: []
ecosystems: []
tags: ["hyper-v", "linux-kernel", "mshv-vtl", "runtime"]
not_affected_if: ["no-mshv-vtl-driver"]
published_at: "2026-10-28T11:17:37+00:00"
first_seen_at: "2026-10-28T11:32:36+00:00"
updated_at: "2026-10-28T11:35:38+00:00"
sources: [{"source": "nvd", "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-99168", "first_seen_at": "2026-10-28T11:32:36+00:00"}]
---

# Linux kernel: mshv_vtl mmap path can dereference a NULL register page

In the Linux kernel's mshv_vtl driver, a CPU whose register page failed to set up can still be reached through a memory fault, leading to a NULL pointer passed to get_page(). The fix checks the per-CPU register page before taking its reference and returns a bus error when it is missing.

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

## Fix

- Update the Linux kernel to a release that includes the upstream commit fixing mshv_vtl_fault() (the sources do not name a version)

## Timeline

- 2026-10-28T11:32:36+00:00 nvd https://nvd.nist.gov/vuln/detail/CVE-2026-99168

## From the sources

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

mshv_vtl: Check per-CPU register page before mmap

Register-page setup is optional for each CPU. If allocation or
registration fails, mshv_vtl_configure_reg_page() warns and leaves that
CPU's reg_page NULL, but initial context setup continues successfully.
Meanwhile, successful setup on another CPU sets the global
mshv_has_reg_page flag.

mshv_vtl_fault() checks this global flag before selecting the requested
CPU's register page. With mixed setup results across online CPUs, the
check passes even for a CPU with no register page, reaching
get_page(NULL) when userspace faults in that mapping.

Check the selected per-CPU register page before taking its reference and
return VM_FAULT_SIGBUS if it is absent.

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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_