Cloudanix VulnDB

CVE-2026-99251

None

CVSS

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EPSS

0.2%

Published

Nov 3, 2026

CISA due date

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Cloudanix analysis

Monitor only SSVC: Track

A Linux kernel bug on systems running in Microsoft Hyper-V can make the computer get stuck forever during startup under rare processor layout conditions, stopping normal operation.

Exploitation
Other
Attacker needs
Local User
Complexity
Theoretical
Impact
Denial Of Service
Component
OS kernel
Class
Denial of service
Remediation
Upgrade
Effort
Medium
Patch risk
Low

What it actually does

Infinite retry loop in init_vp_index() within Hyper-V drivers when a NUMA node lacks online housekeeping CPUs in the HK_TYPE_MANAGED_IRQ mask, causing the cpumask check to perpetually fail and retry without progress.

Why it matters to the business

Potential system hang or boot failure on Linux instances running under Hyper-V with specific NUMA and CPU isolation configurations, resulting in unplanned downtime and requiring manual intervention or reboot.

How an attack unfolds

An attacker with local access or control over system configuration sets up a NUMA topology where one or more nodes have no housekeeping CPUs for managed IRQs; during kernel initialization the loop in init_vp_index() is entered and never exits, denying service.

How to fix it

Update to a Linux kernel version that includes the fix for the infinite retry loop in init_vp_index(); apply the patch that adds NUMA node skipping for nodes without housekeeping CPUs and updates the early abort check.

How to confirm the fix worked

Boot the patched kernel under the previously triggering NUMA/housekeeping configuration and confirm that init_vp_index() completes without looping; inspect kernel source or dmesg for the updated early abort logic and node-skipping behavior.

Typical attack path

  1. Gain local access or control over kernel boot parameters and NUMA/CPU affinity settings
  2. Configure HK_TYPE_MANAGED_IRQ housekeeping mask to exclude all CPUs on a given NUMA node
  3. Trigger kernel initialization path that calls init_vp_index()
  4. Observe infinite loop causing hang or DoS

How to detect it

Examine boot logs and dmesg for repeated calls or stalls inside init_vp_index(); look for Hyper-V guest initialization traces that never progress past VP index assignment on systems with NUMA nodes.

What your security team should do

  • Prioritize kernel updates on all Hyper-V Linux guests within the next maintenance window
  • Review and document CPU isolation and housekeeping mask configurations in production environments
  • Monitor upstream stable kernel releases for backports of this fix

The record

In the Linux kernel, the following vulnerability has been resolved: Drivers: hv: Avoid infinite retry loop in init_vp_index() There is a retry loop in init_vp_index() where the CPUs from a certain node are stripped out if they have already been in the allocated cpumask or not in HK_TYPE_MANAGED_IRQ housekeeping cpumask. If there is no CPU left, the allocated cpumask is ignored and the process is retried again. However, if the HK_TYPE_MANAGED_IRQ housekeeping cpumask turns out not to contain any CPU in that particular node, that will become an infinite retry loop. This particular problem was reported by sashiko [1]. This should rarely happen, but we still need to guard against this. Fix this infinite loop problem by also skipping NUMA node that has no housekeeping CPU in the inner while loop of init_vp_index(). Also update the early abort check to check for the absence of online housekeeping CPUs instead of just the emptiness of the cpumask. As the outer for loop will only be reached if the housekeeping cpumask has at least one online CPU, a NUMA node with housekeeping CPUs will eventually be found.

Affected packages

Ecosystem Package Introduced Fixed