---
id: CVE-2025-40300
title: 'x86/vmscape: Add conditional IBPB mitigation'
summary: |-
  In the Linux kernel, the following vulnerability has been resolved:

  x86/vmscape: Add conditional IBPB mitigation

  VMSCAPE is a vulnerability that exploits insufficient branch predictor
  isolation between a guest and a userspace hyperviso…
severity: none
vendor: Linux
product: Linux
affected:
  - >-
    Linux >= 15d45071523d89b3fb7372e2135fbd72f6af9506 <
    ac60717f9a8d21c58617d0b34274babf24135835
  - >-
    Linux >= 15d45071523d89b3fb7372e2135fbd72f6af9506 <
    c08192b5d6730a914dee6175bc71092ee6a65f14
  - >-
    Linux >= 15d45071523d89b3fb7372e2135fbd72f6af9506 <
    d5490dfa35427a2967e00a4c7a1b95fdbc8ede34
  - >-
    Linux >= 15d45071523d89b3fb7372e2135fbd72f6af9506 <
    2f4f2f8f860cb4c3336a7435ebe8dcfded0c9c6e
  - >-
    Linux >= 15d45071523d89b3fb7372e2135fbd72f6af9506 <
    15006289e5c38b2a830e1fba221977a27598176c
  - >-
    Linux >= 15d45071523d89b3fb7372e2135fbd72f6af9506 <
    893387c18612bb452336a5881da0d015a7e8f4a2
  - >-
    Linux >= 15d45071523d89b3fb7372e2135fbd72f6af9506 <
    f866eef8d1c65504d30923c3f14082ad294d0e6d
  - >-
    Linux >= 15d45071523d89b3fb7372e2135fbd72f6af9506 <
    34e5667041050711a947e260fc9ebebe08bddee5
  - >-
    Linux >= 15d45071523d89b3fb7372e2135fbd72f6af9506 <
    d7ddc93392e4a7ffcccc86edf6ef3e64c778db52
  - >-
    Linux >= 15d45071523d89b3fb7372e2135fbd72f6af9506 <
    459274c77b37ac63b78c928b4b4e748d1f9d05c8
  - >-
    Linux >= 15d45071523d89b3fb7372e2135fbd72f6af9506 <
    510603f504796c3535f67f55fb0b124a303b44c8
  - >-
    Linux >= 15d45071523d89b3fb7372e2135fbd72f6af9506 <
    9c23a90648e831d611152ac08dbcd1283d405e7f
  - >-
    Linux >= 15d45071523d89b3fb7372e2135fbd72f6af9506 <
    2f8f173413f1cbf52660d04df92d0069c4306d25
  - Linux c51f1e5f57cca88d8d5894b6fad1638f643a99d0
  - Linux 4b3870c343a82cd2df7192cc5149c87205dcc611
  - Linux >= 3.16.57 < 3.17
  - Linux >= 4.4.168 < 4.5
  - Linux 4.16
ssvc:
  exploitation: none
  automatable: 'no'
  technicalImpact: partial
  timestamp: '2026-06-10T20:41:37.391418Z'
published: '2025-09-11'
updated: '2026-09-08'
sourceUpdated: '2026-09-08T08:42:58.519Z'
source: CVEORG
sourceUrl: 'https://www.cve.org/CVERecord?id=CVE-2025-40300'
references:
  - url: 'https://git.kernel.org/stable/c/ac60717f9a8d21c58617d0b34274babf24135835'
  - url: 'https://git.kernel.org/stable/c/c08192b5d6730a914dee6175bc71092ee6a65f14'
  - url: 'https://git.kernel.org/stable/c/d5490dfa35427a2967e00a4c7a1b95fdbc8ede34'
  - url: 'https://git.kernel.org/stable/c/2f4f2f8f860cb4c3336a7435ebe8dcfded0c9c6e'
  - url: 'https://git.kernel.org/stable/c/15006289e5c38b2a830e1fba221977a27598176c'
  - url: 'https://git.kernel.org/stable/c/893387c18612bb452336a5881da0d015a7e8f4a2'
  - url: 'https://git.kernel.org/stable/c/f866eef8d1c65504d30923c3f14082ad294d0e6d'
  - url: 'https://git.kernel.org/stable/c/34e5667041050711a947e260fc9ebebe08bddee5'
  - url: 'https://git.kernel.org/stable/c/d7ddc93392e4a7ffcccc86edf6ef3e64c778db52'
  - url: 'https://git.kernel.org/stable/c/459274c77b37ac63b78c928b4b4e748d1f9d05c8'
  - url: 'https://git.kernel.org/stable/c/510603f504796c3535f67f55fb0b124a303b44c8'
  - url: 'https://git.kernel.org/stable/c/9c23a90648e831d611152ac08dbcd1283d405e7f'
  - url: 'https://git.kernel.org/stable/c/2f8f173413f1cbf52660d04df92d0069c4306d25'
tags:
  - cve.org
epss: 0.00344
epssPercentile: 0.25095
ingestedAt: '2026-09-08T15:33:26.996Z'
---

## Overview

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

x86/vmscape: Add conditional IBPB mitigation

VMSCAPE is a vulnerability that exploits insufficient branch predictor
isolation between a guest and a userspace hypervisor (like QEMU). Existing
mitigations already protect kernel/KVM from a malicious guest. Userspace
can additionally be protected by flushing the branch predictors after a
VMexit.

Since it is the userspace that consumes the poisoned branch predictors,
conditionally issue an IBPB after a VMexit and before returning to
userspace. Workloads that frequently switch between hypervisor and
userspace will incur the most overhead from the new IBPB.

This new IBPB is not integrated with the existing IBPB sites. For
instance, a task can use the existing speculation control prctl() to
get an IBPB at context switch time. With this implementation, the
IBPB is doubled up: one at context switch and another before running
userspace.

The intent is to integrate and optimize these cases post-embargo.

[ dhansen: elaborate on suboptimal IBPB solution ]

## Affected

- `Linux >= 15d45071523d89b3fb7372e2135fbd72f6af9506 < ac60717f9a8d21c58617d0b34274babf24135835`
- `Linux >= 15d45071523d89b3fb7372e2135fbd72f6af9506 < c08192b5d6730a914dee6175bc71092ee6a65f14`
- `Linux >= 15d45071523d89b3fb7372e2135fbd72f6af9506 < d5490dfa35427a2967e00a4c7a1b95fdbc8ede34`
- `Linux >= 15d45071523d89b3fb7372e2135fbd72f6af9506 < 2f4f2f8f860cb4c3336a7435ebe8dcfded0c9c6e`
- `Linux >= 15d45071523d89b3fb7372e2135fbd72f6af9506 < 15006289e5c38b2a830e1fba221977a27598176c`
- `Linux >= 15d45071523d89b3fb7372e2135fbd72f6af9506 < 893387c18612bb452336a5881da0d015a7e8f4a2`
- `Linux >= 15d45071523d89b3fb7372e2135fbd72f6af9506 < f866eef8d1c65504d30923c3f14082ad294d0e6d`
- `Linux >= 15d45071523d89b3fb7372e2135fbd72f6af9506 < 34e5667041050711a947e260fc9ebebe08bddee5`
- `Linux >= 15d45071523d89b3fb7372e2135fbd72f6af9506 < d7ddc93392e4a7ffcccc86edf6ef3e64c778db52`
- `Linux >= 15d45071523d89b3fb7372e2135fbd72f6af9506 < 459274c77b37ac63b78c928b4b4e748d1f9d05c8`
- `Linux >= 15d45071523d89b3fb7372e2135fbd72f6af9506 < 510603f504796c3535f67f55fb0b124a303b44c8`
- `Linux >= 15d45071523d89b3fb7372e2135fbd72f6af9506 < 9c23a90648e831d611152ac08dbcd1283d405e7f`
- `Linux >= 15d45071523d89b3fb7372e2135fbd72f6af9506 < 2f8f173413f1cbf52660d04df92d0069c4306d25`
- `Linux c51f1e5f57cca88d8d5894b6fad1638f643a99d0`
- `Linux 4b3870c343a82cd2df7192cc5149c87205dcc611`
- `Linux >= 3.16.57 < 3.17`
- `Linux >= 4.4.168 < 4.5`
- `Linux 4.16`

## Remediation

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