---
id: "CVE-2026-99216"
kind: "vulnerability"
aliases: ["CVE-2026-99216"]
title: "Linux Hyper-V VMBus: connection state reset leaves host messages flowing"
severity: "unknown"
cvss: null
epss: null
exploited: false
status: "open"
category: "infrastructure"
products: []
ecosystems: []
tags: ["hyper-v", "infrastructure", "linux-kernel", "vmbus"]
not_affected_if: ["bare-metal", "non-hyper-v-hypervisor"]
published_at: "2026-10-28T11:17:43+00:00"
first_seen_at: "2026-10-28T11:32:38+00:00"
updated_at: "2026-10-28T11:33:44+00:00"
sources: [{"source": "nvd", "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-99216", "first_seen_at": "2026-10-28T11:32:38+00:00"}]
---

# Linux Hyper-V VMBus: connection state reset leaves host messages flowing

In the Linux kernel's Hyper-V VMBus driver, error and exit paths force the connection state to DISCONNECTED before vmbus_disconnect() runs, so the unload is skipped and the Hyper-V host can keep sending messages and VMBus interrupts. The sources do not describe a demonstrated attacker exploit or a concrete impact beyond that unclean state.

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

## Timeline

- 2026-10-28T11:32:38+00:00 nvd https://nvd.nist.gov/vuln/detail/CVE-2026-99216

## From the sources

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

Drivers: hv: Don't reset VMBus connection state on error/exit paths

In two places, current code forces vmbus_connection.conn_state to
DISCONNECTED prior to calling vmbus_disconnect(). But vmbus_disconnect()
calls vmbus_initiate_unload(), which unloads the VMBus connection
only if the conn_state is CONNECTED. Consequently, the connection
remains and the Hyper-V host might continue to send messages or post
VMBus interrupts.

The problem was introduced in commit 74347a99e73ae ("x86/Hyper-V:
Unload vmbus channel in hv panic callback"), in that
vmbus_initiate_unload() started checking the current connection
state before doing the unload. This commit removed some occurrences
where conn_state was forced to DISCONNECTED, but these two remained,
apparently due to an oversight at the time.

Fix this by not forcing conn_state to DISCONNECTED during VMBus exit,
or if a failure occurs when establishing the connection in the first
place. Whatever value conn_state has at the time is then read by
vmbus_initiate_unload() to determine if there is a connection to
be unloaded.

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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_