MediumCVE-2026-23100

    Linux Kernel: security vulnerability (CVE-2026-23100)

    Published Last modified Sources: Siemens ProductCERT, Debian LTS, Ubuntu, Debian, SUSE, BSI, CVE.org, EUVD, Msrc Update Guide

    What is affected, what to do

    In the Linux kernel, the following vulnerability has been resolved: mm/hugetlb: fix hugetlb_pmd_shared() Patch series "mm/hugetlb: fixes for PMD table sharing (incl. using mmu_gather)", v3. One functional fix, one performance regression fix, and two related comment fixes.

    Update Linux Kernel to version 5.10.253, Linux Kernel to version 5.15.203, Linux Kernel to version 6.1.167.

    Affected
    • Linux Kernel lt 5.10.239..5.10.253
    • Linux Kernel lt 5.15.186..5.15.203
    • Linux Kernel lt 6.1.142..6.1.167
    • Linux Kernel lt 6.6.72..6.6.127
    • Linux Kernel lt 6.12.9..6.12.74
    • Linux Kernel lt 6.13..6.18.8
    Fixed in
    • Linux Kernel 5.10.253
    • Linux Kernel 5.15.203
    • Linux Kernel 6.1.167
    • Linux Kernel 6.6.127
    • Linux Kernel 6.12.74
    • Linux Kernel 6.18.8
    • Linux Kernel 6.19

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

    Metrics

    5.5

    Priority

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

    Source: NVD, CVSS v3

    5.5

    CVSS v3

    Severity Medium on the scale from 0 to 10.

    Source: Siemens ProductCERT, Debian LTS, Ubuntu, Debian, SUSE, BSI, CVE.org, EUVD, Msrc Update Guide

    0.1 %

    EPSS score

    Low — model estimates < 1% exploitation likelihood.

    Source: FIRST EPSS, percentile 3.7

    Show all metrics
    Severity
    Medium
    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
    41.65 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
    5.5 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
    5.5
    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
    0.1 %
    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
    3.7
    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

    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
    Handle the vulnerability in regular vulnerability handling under Art. 21(2)(e) NIS2.
    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

    In the Linux kernel, the following vulnerability has been resolved: mm/hugetlb: fix hugetlb_pmd_shared() Patch series "mm/hugetlb: fixes for PMD table sharing (incl. using mmu_gather)", v3. One functional fix, one performance regression fix, and two related comment fixes. I cleaned up my prototype I recently shared [1] for the performance fix, deferring most of the cleanups I had in the prototype to a later point. While doing that I identified the other things. The goal of this patch set is to be backported to stable trees "fairly" easily. At least patch #1 and #4. Patch #1 fixes hugetlb_pmd_shared() not detecting any sharing Patch #2 + #3 are simple comment fixes that patch #4 interacts with. Patch #4 is a fix for the reported performance regression due to excessive IPI broadcasts during fork()+exit(). The last patch is all about TLB flushes, IPIs and mmu_gather. Read: complicated There are plenty of cleanups in the future to be had + one reasonable optimization on x86. But that's all out of scope for this series. Runtime tested, with a focus on fixing the performance regression using the original reproducer [2] on x86. This patch (of 4): We switched from (wrongly) using the page count to an independent shared count. Now, shared page tables have a refcount of 1 (excluding speculative references) and instead use ptdesc->pt_share_count to identify sharing. We didn't convert hugetlb_pmd_shared(), so right now, we would never detect a shared PMD table as such, because sharing/unsharing no longer touches the refcount of a PMD table. Page migration, like mbind() or migrate_pages() would allow for migrating folios mapped into such shared PMD tables, even though the folios are not exclusive. In smaps we would account them as "private" although they are "shared", and we would be wrongly setting the PM_MMAP_EXCLUSIVE in the pagemap interface. Fix it by properly using ptdesc_pmd_is_shared() in hugetlb_pmd_shared().

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

    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
    • 6.13 – < 6.18.8
    • 6.6.72 – < 6.6.127
    • —
    • 5.15.186 – < 5.15.203
    • 6.12.9 – < 6.12.74
    • 5.10.239 – < 5.10.253
    • 6.1.142 – < 6.1.167
    • 6.18.8
    • 6.6.127
    • 6.19
    • 5.15.203
    • 6.12.74
    • 5.10.253
    • 6.1.167
    SiemensSIMATIC S7
    • 1500 TM MFP V1.1.1 GNU/Linux subsystem
    • —

    Vendors and products

    Affected operating systems

    Affected operating systems
    Linuxdebianlinuxbookworm
    Linuxdebianlinuxbullseye
    Linuxdebianlinuxtrixie
    Linuxdebianlinux-6.1bullseye
    Linuxlinuxlinux_kernel6.13
    Linuxlinuxlinux_kernel6.19
    Linuxlinuxlinux_kernel—

    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 modifiedLinux

      Show 18 original changes
      Individual changes of this event as published by NVD
      TypeActionBeforeAfter
      Referenceadded
      —
      https://git.kernel.org/stable/c/3a18b452dd5f7f1652c2e92f8ae769aa17a66c9e
      Referenceadded
      —
      https://git.kernel.org/stable/c/51dcf459845fd28f5a0d83d408a379b274ec5cc5
      Referenceadded
      —
      https://git.kernel.org/stable/c/5b2aec77f92265a9028c5f632bdd9af5b57ec3a3
      Referenceadded
      —
      https://git.kernel.org/stable/c/69c4e241ff13545d410a8b2a688c932182a858bf
      Referenceadded
      —
      https://git.kernel.org/stable/c/8ae48255bcb17b32436be97553dca848730d365f
      Referenceadded
      —
      https://git.kernel.org/stable/c/bf3c2affe245cf831866ddc8f736ae6a22cdc11c
      Referenceadded
      —
      https://git.kernel.org/stable/c/ca1a47cd3f5f4c46ca188b1c9a27af87d1ab2216
      Referenceremoved
      https://git.kernel.org/stable/c/3a18b452dd5f7f1652c2e92f8ae769aa17a66c9e
      —
      Referenceremoved
      https://git.kernel.org/stable/c/51dcf459845fd28f5a0d83d408a379b274ec5cc5
      —
      Referenceremoved
      https://git.kernel.org/stable/c/5b2aec77f92265a9028c5f632bdd9af5b57ec3a3
      —
      Referenceremoved
      https://git.kernel.org/stable/c/69c4e241ff13545d410a8b2a688c932182a858bf
      —
      Referenceremoved
      https://git.kernel.org/stable/c/8ae48255bcb17b32436be97553dca848730d365f
      —
      Referenceremoved
      https://git.kernel.org/stable/c/bf3c2affe245cf831866ddc8f736ae6a22cdc11c
      —
      Referenceremoved
      https://git.kernel.org/stable/c/ca1a47cd3f5f4c46ca188b1c9a27af87d1ab2216
      —
      Reference typeremoved
      https://git.kernel.org/stable/c/3a18b452dd5f7f1652c2e92f8ae769aa17a66c9e Types: Patch
      —
      Reference typeremoved
      https://git.kernel.org/stable/c/51dcf459845fd28f5a0d83d408a379b274ec5cc5 Types: Patch
      —
      Reference typeremoved
      https://git.kernel.org/stable/c/69c4e241ff13545d410a8b2a688c932182a858bf Types: Patch
      —
      Reference typeremoved
      https://git.kernel.org/stable/c/ca1a47cd3f5f4c46ca188b1c9a27af87d1ab2216 Types: Patch
      —

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

    2. Record modifiedSiemens ADP

      Show 7 original changes
      Individual changes of this event as published by NVD
      TypeActionBeforeAfter
      Affected versions (publisher)added
      —
      Affected value modified. <a href="https://github.com/CVEProject/cvelistV5/blob/main/cves/2026/23xxx/CVE-2026-23100.json">CVE-2026-23100</a>
      Referenceadded
      —
      https://cert-portal.siemens.com/productcert/html/ssa-019113.html
      Referenceadded
      —
      https://cert-portal.siemens.com/productcert/html/ssa-082556.html
      Referenceadded
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      https://cert-portal.siemens.com/productcert/html/ssa-457936.html
      Referenceadded
      —
      https://cert-portal.siemens.com/productcert/html/ssa-784472.html
      Referenceremoved
      https://cert-portal.siemens.com/productcert/html/ssa-019113.html
      —
      Referenceremoved
      https://cert-portal.siemens.com/productcert/html/ssa-082556.html
      —

      Source identifier: 0b142b55-0307-4c5a-b3c9-f314f3fb7c5e

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