---
id: CVE-2026-63940
title: 'KVM: SEV: Ignore Port I/O requests of length ''0'''
summary: |-
  In the Linux kernel, the following vulnerability has been resolved:

  KVM: SEV: Ignore Port I/O requests of length '0'

  Explicitly ignore Port I/O requests of length '0' (or count '0'), so that
  setting up the software scratch area (and ot…
severity: critical
cvss: 9.3
cvssVector: 'CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H'
cvssSource: cna
vendor: Linux
product: Linux
affected:
  - >-
    Linux >= 291bd20d5d88814a73d43b55b9428feab2f28094 <
    3b6035bc6bff20e89752ce4358bc4c9a9d5883f2
  - >-
    Linux >= 291bd20d5d88814a73d43b55b9428feab2f28094 <
    2254972d4d69e279ba4e87bf0968eb08ad0d3c92
  - >-
    Linux >= 291bd20d5d88814a73d43b55b9428feab2f28094 <
    c30cde934c7813b4e3069765dac64ce3d31e34f2
  - >-
    Linux >= 291bd20d5d88814a73d43b55b9428feab2f28094 <
    3988bd2723de407ae90fa7a6f6029b4e60238c58
  - Linux 5.11
ssvc:
  exploitation: none
  automatable: 'no'
  technicalImpact: total
  timestamp: '2026-10-16T15:33:50.957635Z'
published: '2026-07-19'
updated: '2026-10-16'
sourceUpdated: '2026-10-16T15:42:13.419Z'
source: CVEORG
sourceUrl: 'https://www.cve.org/CVERecord?id=CVE-2026-63940'
references:
  - url: 'https://git.kernel.org/stable/c/3b6035bc6bff20e89752ce4358bc4c9a9d5883f2'
  - url: 'https://git.kernel.org/stable/c/2254972d4d69e279ba4e87bf0968eb08ad0d3c92'
  - url: 'https://git.kernel.org/stable/c/c30cde934c7813b4e3069765dac64ce3d31e34f2'
  - url: 'https://git.kernel.org/stable/c/3988bd2723de407ae90fa7a6f6029b4e60238c58'
tags:
  - cve.org
epss: 0.00185
epssPercentile: 0.07565
ingestedAt: '2026-10-16T17:24:46.781Z'
---

## Overview

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

KVM: SEV: Ignore Port I/O requests of length '0'

Explicitly ignore Port I/O requests of length '0' (or count '0'), so that
setting up the software scratch area (and other code) doesn't have to
worry about underflowing the length, and to allow for WARNing on trying
to configure the scratch area with len==0.

## Affected

- `Linux >= 291bd20d5d88814a73d43b55b9428feab2f28094 < 3b6035bc6bff20e89752ce4358bc4c9a9d5883f2`
- `Linux >= 291bd20d5d88814a73d43b55b9428feab2f28094 < 2254972d4d69e279ba4e87bf0968eb08ad0d3c92`
- `Linux >= 291bd20d5d88814a73d43b55b9428feab2f28094 < c30cde934c7813b4e3069765dac64ce3d31e34f2`
- `Linux >= 291bd20d5d88814a73d43b55b9428feab2f28094 < 3988bd2723de407ae90fa7a6f6029b4e60238c58`
- `Linux 5.11`

## Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.