HighCVE-2025-40026

    Linux Kernel: security vulnerability (CVE-2025-40026)

    Published Last modified Sources: Debian LTS, BSI, Debian, Red Hat, EUVD, CVE.org, Msrc Update Guide

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    What is affected, what to do

    A flaw was found in the Kernel-based Virtual Machine (KVM) for x86. This vulnerability occurs when KVM incorrectly re-checks Level 1 (L1) intercepts during the completion of userspace I/O emulation for a Level 2 (L2) instruction.

    Update Linux Kernel to version 5.4.301, Linux Kernel to version 5.10.246, Linux Kernel to version 5.15.195.

    Affected
    • Linux Kernel lt 3.0..5.4.301
    • Linux Kernel lt 5.5..5.10.246
    • Linux Kernel lt 5.11..5.15.195
    • Linux Kernel lt 5.16..6.1.157
    • Linux Kernel lt 6.2..6.6.111
    • Linux Kernel lt 6.7..6.12.52
    • Linux Kernel lt 6.13..6.16.12
    • Linux Kernel lt 6.17..6.17.2
    Fixed in
    • Linux Kernel 5.4.301
    • Linux Kernel 5.10.246
    • Linux Kernel 5.15.195
    • Linux Kernel 6.1.157
    • Linux Kernel 6.6.111
    • Linux Kernel 6.12.52
    • Linux Kernel 6.16.12
    • Linux Kernel 6.17.2
    • Linux Kernel 6.18

    Not sure whether and how you are affected? Ask a question about this vulnerability

    Metrics

    7.9

    Priority

    XIEM Effective CVSS: highest available CVSS rating from NVD and vendor data.

    Source: NVD, CVSS v3

    7.9

    CVSS v3

    Severity High on the scale from 0 to 10.

    Source: Debian LTS, BSI, Debian, Red Hat, EUVD, CVE.org, Msrc Update Guide

    0.2 %

    EPSS score

    Low — model estimates < 1% exploitation likelihood.

    Source: FIRST EPSS, percentile 6.4

    Show all metrics
    Severity
    High
    Priority (0–325)

    The priority score is a consolidated metric that condenses several individual signals into a single, action-guiding ranking: technical severity (CVSS), exploitation likelihood (EPSS), known-exploited status (KEV) and the context of the affected asset. The aim is to answer the only truly important question in vulnerability management: what first?

    Read in glossary
    51.46 Methodology
    Exploit maturity

    An exploit is code or a technique that specifically uses a concrete vulnerability to force unintended behaviour — such as executing code or escalating privileges. It is the tool that turns a theoretical flaw into a practical attack.

    Read in glossary
    no public PoC known
    XIEM Effective CVSS

    XIEM® is the tiered managed-security operating model from NEOSEC and a registered trademark of NEOSEC GmbH. It extends classic SIEM — the central collection, normalisation and correlation of security-relevant events — with endpoint forensics, network visibility and deception technology, and consolidates them into three building tiers: Sentry, Orchestrate and Command.

    Read in glossary
    7.9 Methodology
    CVSS v3

    CVSS is the globally established, open standard for assessing the technical severity of a vulnerability on a scale from 0 to 10. It describes how easily a flaw can be exploited and what damage it can cause — but not how likely its actual exploitation is. CVSS and the complementary EPSS deliberately answer different questions.

    Read in glossary
    7.9
    EPSS score

    The EPSS score is the absolute model output for an individual vulnerability: the estimated probability of real-world exploitation within the next 30 days, expressed as a value between 0 and 1 (i.e. 0 % to 100 %). A score of 0.42 means „the model estimates a 42 % chance of real-world exploitation within 30 days“.

    Read in glossary
    0.2 %
    Low — model estimates < 1% exploitation likelihood.
    EPSS percentile

    The EPSS percentile is the relative position of a vulnerability within all EPSS-scored CVEs, expressed as a value between 0 and 1. A percentile of 0.90 means „this CVE has a higher EPSS score than 90 % of all other scored CVEs“. Unlike the EPSS score, it is not a probability — but a positioning within a ranking.

    Read in glossary
    6.4
    Low — this CVE sits in the lower 10% of all CVEs scored today.
    KEV status

    The KEV catalogue is a list maintained by the US authority CISA of vulnerabilities for which active exploitation in the wild has been confirmed. It answers not the question „how severe?“ but „is it already being attacked?“ — thereby sharply prioritising patching.

    Read in glossary
    —
    Published
    CISA assessment (SSVC)
    Exploitation: none known · not automatable · Technical impact: partial
    Source: CISA Vulnrichment, as of 15 October 2026

    Detection rules

    No NEOSEC detection rule is available for this vulnerability yet.

    Classification under NIS2 and CRA

    Rule-based classification from exploitation status and severity. It does not replace a case-by-case assessment.

    NIS2

    NIS2 is EU Directive (EU) 2022/2555 to raise the level of cybersecurity across the Union. It substantially broadens obligations compared with the first NIS directive: more sectors, mandatory risk management, staged reporting duties and personal accountability of senior management.

    Read in glossary
    High technical severity: assess and remediate the vulnerability in vulnerability handling under Art. 21(2)(e) NIS2 and document the decision.
    CRA

    The CRA is EU Regulation (EU) 2024/2847 setting horizontal cybersecurity requirements for „products with digital elements“ — from industrial controllers and software to connected consumer devices. For the first time manufacturers must ensure security across the entire product lifecycle, handle vulnerabilities and provide security updates.

    Read in glossary
    From 11.12.2027, Annex I Part II CRA requires manufacturers of affected products with digital elements to handle vulnerabilities without delay and provide security updates.
    ISO/IEC 27001

    ISO/IEC 27001 is the internationally leading standard for an information security management system (ISMS). It describes a risk-based, process-oriented framework to systematically plan, implement, review and improve information security.

    Read in glossary
    Control A.8.8, management of technical vulnerabilities: assess relevance to your systems, plan remediation and keep evidence.

    Description

    A flaw was found in the Kernel-based Virtual Machine (KVM) for x86. This vulnerability occurs when KVM incorrectly re-checks Level 1 (L1) intercepts during the completion of userspace I/O emulation for a Level 2 (L2) instruction. If the L1 or host userspace modifies I/O interception settings during this process, KVM may misinterpret already-emulated I/O as intercepted. This can lead to a kernel warning and potentially disrupt the guest virtual machine, resulting in a denial of service. Exploitation requires local access to /dev/kvm and the ability to perform nested virtualization or manipulate I/O bitmaps.

    Source: Debian LTS Advisories, BSI WID Portal, BSI CSAF, Debian Security Advisories, redhat_csaf, ENISA EUVD, NVD (NIST), Microsoft Security Update Guide, CVE.org (MITRE), cvelistv5

    Affected products

    The following versions are affected. Older releases of the same product line are also vulnerable unless stated otherwise.

    Affected products
    Affected versionsFixed in
    LinuxLinux
    • 5.5 – < 5.10.246
    • 6.17 – < 6.17.2
    • —
    • 6.13 – < 6.16.12
    • 5.16 – < 6.1.157
    • 3.0 – < 5.4.301
    • 5.11 – < 5.15.195
    • 6.7 – < 6.12.52
    • 6.2 – < 6.6.111
    • 5.10.246
    • 6.17.2
    • 6.18
    • 6.16.12
    • 6.1.157
    • 5.4.301
    • 5.15.195
    • 6.12.52
    • 6.6.111
    IBMQRadar SIEM
    • <7.5.0 UP15 IF06
    • —
    MicrosoftAzure
    • Linux Kernel <6.6.104.2-4 on Linux 3.0
    • —

    Vendors and products

    Affected operating systems

    Affected operating systems
    Linuxdebianlinuxbookworm
    Linuxdebianlinuxbullseye
    Linuxdebianlinux-6.1bullseye

    References & sources

    Changes to this CVE

    Who changed this CVE and when: NVD (analysis, affected products, CVSS), the CVE publisher (CNA) and additional providers such as CISA (ADP).

    1. Record modifiedCISA ADP

      CISA assessment (SSVC): exploitation: none known, automatable: no

      Show the original change
      Individual changes of this event as published by NVD
      TypeActionBeforeAfter
      SSVC assessmentadded
      —
      {"id":"CVE-2025-40026","role":"CISA Coordinator","options":[{"exploitation":"none"},{"automatable":"no"},{"technicalImpact":"partial"}],"version":"2.0.3","timestamp":"2026-10-15T21:56:14.274469Z"}

      Source identifier: 134c704f-9b21-4f2e-91b3-4a467353bcc0

    2. Record modifiedLinux

      Show 18 original changes
      Individual changes of this event as published by NVD
      TypeActionBeforeAfter
      Referenceadded
      —
      https://git.kernel.org/stable/c/00338255bb1f422642fb2798ebe92e93b6e4209b
      Referenceadded
      —
      https://git.kernel.org/stable/c/3a062a5c55adc5507600b9ae6d911e247e2f1d6e
      Referenceadded
      —
      https://git.kernel.org/stable/c/3d3abf3f7e8b1abb082070a343de82d7efc80523
      Referenceadded
      —
      https://git.kernel.org/stable/c/7366830642505683bbe905a2ba5d18d6e4b512b8
      Referenceadded
      —
      https://git.kernel.org/stable/c/a908eca437789589dd4624da428614c1275064dc
      Referenceadded
      —
      https://git.kernel.org/stable/c/ba35a5d775799ce5ad60230be97336f2fefd518e
      Referenceadded
      —
      https://git.kernel.org/stable/c/e0ce3ed1048a47986d15aef1a98ebda25560d257
      Referenceadded
      —
      https://git.kernel.org/stable/c/e7177c7e32cb806f348387b7f4faafd4a5b32054
      Referenceadded
      —
      https://git.kernel.org/stable/c/e750f85391286a4c8100275516973324b621a269
      Referenceremoved
      https://git.kernel.org/stable/c/00338255bb1f422642fb2798ebe92e93b6e4209b
      —
      Referenceremoved
      https://git.kernel.org/stable/c/3a062a5c55adc5507600b9ae6d911e247e2f1d6e
      —
      Referenceremoved
      https://git.kernel.org/stable/c/3d3abf3f7e8b1abb082070a343de82d7efc80523
      —
      Referenceremoved
      https://git.kernel.org/stable/c/7366830642505683bbe905a2ba5d18d6e4b512b8
      —
      Referenceremoved
      https://git.kernel.org/stable/c/a908eca437789589dd4624da428614c1275064dc
      —
      Referenceremoved
      https://git.kernel.org/stable/c/ba35a5d775799ce5ad60230be97336f2fefd518e
      —
      Referenceremoved
      https://git.kernel.org/stable/c/e0ce3ed1048a47986d15aef1a98ebda25560d257
      —
      Referenceremoved
      https://git.kernel.org/stable/c/e7177c7e32cb806f348387b7f4faafd4a5b32054
      —
      Referenceremoved
      https://git.kernel.org/stable/c/e750f85391286a4c8100275516973324b621a269
      —

      Source identifier: 416baaa9-dc9f-4396-8d5f-8c081fb06d67

    3. Record modifiedLinux

      CVSS V3.1: AV:L/AC:L/PR:L/UI:N/S:C/C:L/I:L/A:H

      Show the original change
      Individual changes of this event as published by NVD
      TypeActionBeforeAfter
      CVSSadded
      —
      AV:L/AC:L/PR:L/UI:N/S:C/C:L/I:L/A:H

      Source identifier: 416baaa9-dc9f-4396-8d5f-8c081fb06d67

    One NVD translation into another language is hidden.

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